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Program ASTROCLK
Astronomical Clock and Celestial Tracking Program
with Celestial Navigation
by David H. Ransom, Jr.
Rancho Palos Verdes, CA
Version 8947
November 19, 1989
ASTROCLK Astronomical Clock and Celestial Tracking Program Page i
TABLE OF CONTENTS
ACKNOWLEDGEMENTS.........................................1
INTRODUCTION.............................................2
HARDWARE REQUIREMENTS....................................7
PROGRAM OPERATION........................................10
Required ASTROCLK Files...............................10
Starting Program ASTROCLK.............................12
Running Program ASTROCLK..............................13
FUNCTION KEYS AND HELP...................................18
F1 Display HELP Screens...............................18
F2 Display Target Object EPHEMERIS....................18
F3 Set Time and/or Date...............................18
Read Hardware Clock................................19
Set ALARM or INTERVAL TIMER Time...................19
F4 Toggle Clocks ON or OFF............................19
Enable Simulated Real Time.........................19
F5 Set Target Coordinates.............................20
Enter USNO Star Name or Number.....................20
Search for Nearest USNO Star.......................20
Search EXTERNAL STAR CATALOG by Name or ID.........20
Search EXTERNAL STAR CATALOG by RA and DEC.........21
Search EXTERNAL STAR CATALOG for Nearest Star......21
Manual Target Data Entry...........................21
Set Polaris Coordinates............................22
F6 Set Local Coordinates..............................23
Set Destination Coordinates........................23
Set Local Conditions...............................23
F7 Set Display Format.................................23
Change Target Display Coordinates..................24
F8 Precess Internal Star Database.....................24
F9 DOS Shell..........................................25
Execute Preset DOS Command.........................25
Execute USNO Ephemeris (ICE or FA).................25
F10 Celestial Navigation...............................26
Setting Program Options............................26
0-9 Select Display Window Mode.........................26
SETTING PROGRAM OPTIONS..................................28
Setting the DAYLIGHT FLAG.............................28
Setting the ZONE CORRECTION...........................29
Setting the COLOR FLAG................................29
Setting the ICE/FA FLAG...............................30
Setting the CALENDAR FLAG.............................30
Setting the FILE NAMES and PATHS......................31
Setting the PRESET DOS COMMAND........................33
SETTING LOCAL/UT/TDT TIME AND DATE.......................34
Setting the LOCAL/UT/TDT Time.........................36
ASTROCLK Astronomical Clock and Celestial Tracking Program Page ii
Setting the LOCAL/UT Date.............................37
SETTING LOCAL AND DESTINATION COORDINATES................39
SETTING LOCAL CONDITIONS.................................43
DUAL-TIME DISPLAYS.......................................44
ALARM AND INTERVAL TIMER OPERATIONS......................46
Using the ALARM Function..............................46
Using the INTERVAL TIMER..............................47
Linked ALARM & INTERVAL TIMER Operation...............48
TARGET TRACKING DISPLAY..................................49
TARGET OBJECT EPHEMERIS..................................53
PRECISION TIME AND DATA DISPLAYS.........................55
Precision Time Display #1.............................55
Precision Time Display #2.............................57
Precision Data Display #1.............................57
Precision Data Display #2.............................58
Precision Data Display #3.............................59
PLANETARY DATA DISPLAYS..................................60
MINOR PLANET SELECTION...................................64
Entering Orbital Parameters...........................67
CELESTIAL NAVIGATION.....................................69
Setting UT TIME ZONE OFFSET...........................70
Navigation by Dead Reckoning..........................73
Celestial Navigation with Star Sights.................80
Selecting USNO Navigational Stars.....................84
Celestial Navigation Example..........................86
SIDEREAL TIME AND EQUATORIAL COORDINATES.................90
USNO COMPUTER EPHEMERIS PROGRAMS, ICE AND FA.............92
USNO STANDARD NAVIGATIONAL STARS.........................95
CONSTELLATIONS AND NAMES.................................97
USING EXTERNAL STAR CATALOGS.............................101
PRECESSION AND STELLAR MOTION............................104
DATES AND THE GREGORIAN CALENDAR.........................106
WHAT TIME IS IT?.........................................112
PRECISION AND ACCURACY TESTS.............................118
Compiler..............................................118
Calendar Dates........................................119
Julian Dates..........................................120
Universal Times (UT and UTC)..........................120
Terrestrial Dynamical Time (TDT, ET and Delta T)......120
Atomic Times (TAI and A.1)............................121
Sidereal Times (GMST and GAST)........................121
Precession............................................122
Solar Position Calculations...........................124
Major Planet Position Calculations....................127
Minor Planet Position Calculations....................128
Celestial Navigation Calculations.....................128
J2000.0 Internal Star Database........................130
ASTROCLK MESSAGES AND ERRORS.............................131
ASTROCLK Numbered Errors and Cautions.................131
Other ASTROCLK, QuickBASIC and DOS Errors.............137
A BRIEF EDITORIAL........................................139
BIBLIOGRAPHY.............................................142
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 1
ACKNOWLEDGEMENTS
Few tasks of any consequence are accomplished unaided. For
ASTROCLK, in addition to the numerous references cited in the
BIBLIOGRAPHY, there are several individuals to whom special
thanks are due.
Ward Harman, a retired engineer living near me in Palos
Verdes, California, has spent many hours testing and validating
the performance of various aspects of ASTROCLK, advising me of
errors when he found them, and making numerous suggestions with
respect to both style and substance.
Steve Brewster, of Stony Ridge Observatory high above
Pasadena, California, has been most generous with his time,
advice, and encouragement. To all of that, he added a long and
fascinating evening at the Observatory where we were able to
experience firsthand the thrill of "real" astronomy using SRO's
30-inch reflector and which helped me to better understand how
ASTROCLK might be used in that environment.
And to all of those interested astronomy and computer
enthusiasts who have called, written, or left messages for me on
my bulletin board system, my thanks for your kind words and
suggestions. Those letters and calls inform me that ASTROCLK is
being used in Europe, Hong Kong, Japan, Israel, and Australia in
addition to the United States and Canada. I must be doing
something right! ASTROCLK is now embarking upon its third year.
Finally, and by no means least, my wife Vicki has been both
patient and supportive during the many hundreds of hours I have
spent hunched over one or another of my computers as ASTROCLK has
evolved from a simple sidereal clock to the complex program it is
today. It was her interest in, and curiousity about, astronomy
and the night sky which helped inspire my efforts in the first
place, and her encouragement has been essential during the years
that I have invested in ASTROCLK.
November, 1989
David H. Ransom, Jr.
Rancho Palos Verdes, CA
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 2
INTRODUCTION
Program ASTROCLK is an Astronomical Clock and Celestial
Tracking Program. ASTROCLK is free for non-commercial use. Use it
if you like it, discard it if you don't. There are no warranties
of any kind. If you wish to use ASTROCLK commercially, write for
license information. For information on how to obtain the most
recent version of the program, see the section A BRIEF EDITORIAL.
And now, on with the story ...
Like many people, I have long been fascinated by the stars
at night and by things astronomical. But it was not until some
years ago, when I spent considerable time in the foothills of
Northern California, that I regularly saw the night sky without
the interference of city lights. There followed a heightened
interest in the stars and a desire to be able to recognize the
various constellations and important individual stars. Many
books, star charts, and cold winter nights later the age of the
Personal Computer dawned. Suddenly, I realized, I had a tool
which would enable me to figure out many of these things on my
own and practically in real time.
Program ASTROCLK has evolved from a series of smaller
programs, each designed to calculate some little piece of
astronomical data which I needed or wanted for use with my hobby.
Each time that I needed still another bit of data in order to do
something, I'd search out the necessary formulae or methods and
write a new little program to automate the process. After a
relatively short period of time I discovered that I had literally
dozens of such small programs, but no single program was ever
sufficient to get me all the information I sought at a particular
time.
Equally frustrating, none of the stand-alone programs
available or that I had written up to that point gave me the
information in real time, adjusted for my geographical location.
I always had to look up all the things I'd forgotten or run
a number of programs to get the data I sought. And to further
complicate things, there are an almost unbelievable number of
different methods for telling time, of which perhaps half a dozen
or so are useful to the casual astronomer or navigator. I finally
mastered the zone changes from Greenwich to Los Angeles, but
converting local time to sidereal time ("star time", if you
prefer) in my head has so far eluded me. Program ASTROCLK was
intended to solve all of these problems for me. While it is still
some distance from accomplishing that rather ambitious goal, it's
a very big step along the way. I'm starting to run out of
"necessary" features to add!
As with any profession, astronomers and navigators have
developed a technical language all their own to describe the
phenomenae of time and celestial mechanics. Not only is this
language almost as complex as the science it seeks to describe,
but many seemingly common words carry definitions far divorced
from everyday life and our intuitive understanding of their
meaning. The amateur astronomer or layman can easily become
hopelessly confused, particularly as not all texts,
organizations, and related professions necessarily use precisely
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 3
the same words or even the same definitions to describe a given
measurement or item of data. All too frequently the definitions
have changed over time, and sometimes they are even reversed from
one discipline to another.
For my own understanding and entertainment, I have spent
considerable time researching the subject and attempting to
assemble a consistent set of computer programs and algorithms to
facilitate the practical use of my personal computers in
astronomy and navigation. Program ASTROCLK now represents a
continuing effort spanning almost two years and more than a
thousand hours of work. I hope that effort is judged worthwhile.
The advent of the truly portable personal computer has
served as an additional spur to these efforts so that I may have
the information at my fingertips no matter where I may travel.
There are moments when I wonder who is the slave and who the
servant.
I have used many and varied sources and have made every
effort to assure the accuracy of the information and calculations
presented. However, I alone am responsible for the final outcome
-- along with any errors that may be discovered. My thanks to
those individuals who have taken the time to report problems and
suggest improvements. Without their interest and encouragement, I
doubt that ASTROCLK would have become what it is or that my
efforts would have continued.
The first and most important order of business for any
astronomer or navigator is to know what time it is. For ASTROCLK,
I assume that the computer's internal clock has been set to the
correct local time, keeps reasonably good time, and that the
relationship between local time and Coordinated Universal Time
can be calculated or is known. To a high degree of accuracy,
what is now known as Coordinated Universal Time (UTC) was
previously called Greenwich Mean Time; there are those who still
insist on using the old name. The U. S. military forces, ever
adept at finding a different name for things we might otherwise
recognize, refer to UTC as Zulu Time. In the United States, the
National Bureau of Standards continuously broadcasts UTC on
stations WWV (Fort Collins, Colorado) and WWVH (Kauai, Hawaii);
the frequencies transmitted are: 2.5MHz, 5MHz, 10MHz, 15MHz and
20MHz (WWV only). Reception will vary depending upon the time of
day, geographic location, and current atmospheric conditions. In
Europe and in many places around the world, the BBC World Service
gives a time signal every hour which is synchronized with
Greenwich Mean Time, essentially identical with UTC.
As an aside, I have noticed that the hardware clocks in my
computers maintain more accurate time than do the software clocks
(particularly with versions of MS-DOS prior to 3.xx). Further,
some programs which use high speed serial communications disable
the software clock during operation and the time errors can
become substantial. Other software can also suspend timekeeping
functions for brief intervals. On my Zenith Z-248 system (an IBM
AT-compatible), for example, use of the program BROOKLYN BRIDGE
(inter-computer communications) can introduce errors of tens of
seconds or more. I recommend that you first check the accuracy of
your software clock, the one that keeps track of time after you
begin using the computer, over a period of several hours. An easy
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 4
way to do this is simply to run ASTROCLK and observe the
displayed local time compared to an accurate clock or watch.
Second, if you temporarily leave ASTROCLK using Function Key F9,
note the time when you return to ASTROCLK and, if the time is in
error, make a note of what programs or operations in your system
affect the accuracy of the software clock. In either case, reset
your software clock from time to time if necessary or, if your
computer has a hardware clock, re-read your hardware clock to
take advantage of its superior accuracy. For many computers,
ASTROCLK can do this using Function Key ALT-F3.
Using this more or less accurate time standard, ASTROCLK
displays the current Local Time and Local Date, the Local Mean
Sidereal Time ("star time"), and the Local Mean Solar Time
(referred to the local longitude). Also shown are: Coordinated
Universal Time (UTC) which, for years 1925 and later and to the
accuracy used here, is the same as Greenwich Mean Time (GMT); the
UTC Date at the Prime Meridian (Greenwich, longitude 0 degrees);
Greenwich Mean Sidereal Time; and, the local time zone relative
to UTC. All times are in 24-hour notation and local time is Local
Standard Time or Local Daylight Time, depending upon the setting
of the DAYLIGHT FLAG. If your time zone is offset from the
computed local time zone, see also the section SETTING PROGRAM
OPTIONS. Note that dates are shown as DD-MM-YYYY (European style,
day-month-year) and that because of the time span covered the
full 4-digit year is required. Any one of the times may be
displayed in a main window with extra large digits for easy
visibility.
Precision Time and Data Displays are available which show a
variety of common time standards to a precision of 0.0001 seconds
along with other astronomical information. The display is updated
each second -- provided the computer can make the necessary
calculations in that time. If the clocks are stopped, the user
may enter any desired time and date and view the calculated
values for all of these items to a high degree of accuracy. The
values have been carefully checked against the Astronomical
Almanac, prepared each year jointly by the U. S. Naval
Observatory (USNO) and the Royal Greenwich Observatory, and the
USNO Floppy Almanac and are believed accurate to within plus or
minus 0.01 seconds or better; note that the displayed precision
is 0.0001 seconds.
Initially, the program assumes the geographical location of
Rancho Palos Verdes, California, near Los Angeles. However, an
auxiliary file contains the names and locations of a number of
American and Canadian cities which can quickly be read by
ASTROCLK. The file may easily be edited to include your favorite
locations and their coordinates. If you change the local
coordinates, ASTROCLK saves them in a special file, ASTROCLK.INI,
and the new place name and coordinates will be automatically
loaded when the program is next started.
A tracking feature is included which allows the user to
continuously display the celestial and horizon (observer)
coordinates for the pole star, Polaris, and the 57 stars
designated by the U. S. Naval Observatory (USNO) as "Standard
Navigational Stars". Data for these stars are preset in the
program and are for Epoch J2000.0, the current standard epoch for
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 5
celestial coordinates. The list of these standard stars is from
USNO, and the actual coordinates have been taken from the USNO
Floppy Almanac 1988. The data for proper motion is also included
for the correct calculation of precession.
Alternatively, the user may search an external star catalog
for a desired star using the catalog number or any of several
star names. The supplied catalog, ASTROCLK.CAT, contains 1645
stars and objects whose coordinates have been calculated by USNO
and which are also for Epoch J2000.0. Finally, the user may
manually enter the celestial coordinates (right ascension and
declination) for a star, planet, or other object. Once the
celestial coordinates have been selected or entered, ASTROCLK
continually displays the local (or "observer horizon")
coordinates as well as the Sidereal Hour Angle (SHA, preferred by
navigators), computed once per second. The program also displays
coordinates adjusted for atmospheric refraction, important as an
object approaches the horizon. Using a small portable computer,
the would-be stargazer may take the program into the field and
use it to locate and track the desired object.
The user may also enter the local horizon coordinates,
Altitude and Azimuth, for a bright star and ask ASTROCLK to
select the USNO Standard Navigational Star which is closest to
the position entered at that time. It will also find Polaris if
the coordinates are close enough, but the algorithm for star
selection is less accurate near the poles. The same process may
be used with the external star catalog. So the program works both
ways: it can tell you where to look for a selected star or, if
you tell it where you see a star, it can tell you which star you
are probably looking at.
By stopping the real time clock and entering a date and time
of choice, the user may also determine the position of a
celestial object at any time in the past or future. However,
since some formulae and star coordinates assume the present
epoch, J2000.0 usually, the accuracy of positions calculated may
decrease for epochs distant from modern times. A simulation mode
may be used to view data in simulated real time at any preset
time and date.
When desired, ASTROCLK will perform the calculations
required to predict the coordinates of the major planets or,
using an external catalog, of minor planets, comets, and
asteroids. ASTROCLK can display a variety of information for the
planets, and will provide tracking data as with the USNO Standard
Navigation Stars. The accuracy of the planetary positions has not
been checked over longer time spans. See the sections PLANETARY
DATA DISPLAYS and MINOR PLANET SELECTION for further discussion.
Inspired by several long sea journeys, ASTROCLK can perform
a number of navigational functions, including dead reckoning and
celestial navigation. While the accuracy is not quite as high as
can be achieved with the Nautical Almanac (and a lot of tiresome
calculations) or by sophisticated satellite navigation systems,
it is sufficient to get in the right neighborhood. With "perfect"
star sights, the accuracy is approximately 0.25 nautical miles.
ASTROCLK includes a perpetual calendar which will display
any month of any year from -4713 B.C. into the future. The
default calendar algorithms follow the Julian Calendar from -4713
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 6
B.C. until October 4, 1582 after which the Gregorian Calendar is
used. This follows civil usage in catholic countries as well as
astronomical convention, but will not correspond to the date
convention used in countries which did not adopt the Gregorian
Calendar in October of 1582. Great Britain and its colonies
(including what is now the United States), for example, did not
adopt the Gregorian Calendar until September 2, 1752. Dates prior
to the introduction of the Julian Calendar in 46 A.D. are in
accordance with the Julian Proleptic Calendar (the Julian
Calendar extended backwards in time from 46 A.D.) and are
therefore more or less a figment of the program's imagination;
the dates computed are consistent with that calendar (and
astronomical convention) but bear no relation to any calendar in
actual use at the time. A program option is available to choose
between the strict Julian calendar and either the 1582 or the
1752 adoption of the Gregorian calendar. An additional date
display is also available which shows several styles of Julian
Date, the local date, the current day of the year, and the day of
the week.
ASTROCLK is presently being used at several observatories
for both time and tracking displays. Beginning with Version 8903,
the display may be set to the RED mode so that all displays are
presented in red; the monitor intensity may then be adjusted for
best comfort and protection of night vision. A GREEN mode is also
available which may reduce eye fatigue during periods of extended
use.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 7
HARDWARE REQUIREMENTS
ASTROCLK was designed for and is best operated using a color
adapter and color monitor, CGA/EGA/VGA. The program can be forced
to emulate monochrome output on color video adapters with the
"/M" command line option. Limited tests on a monochrome system
(true monochrome adapter and display, as opposed to a system
using a monochrome display on a color-compatible adapter), have
been successful when used with the "/M" command line option. The
program has so far been tested on the following systems:
ALR 20386DT Computer
VGA Video Graphics Adapter (Paradise VGA Plus)
VGA High Resolution Color Display (Zenith ZCM-1490)
80387 math coprocessor
Zenith Z-386 Computer
VGA Video Graphics Adapter (Zenith Z-449)
VGA High Resolution Color Display (Zenith ZCM-1490)
80287 math coprocessor
Zenith Z-248 (IBM PC-AT compatible)
VGA Video Graphics Adapter (Paradise VGA Professional)
VGA High Resolution Color Display (Zenith ZCM-1490)
80287 math coprocessor
Zenith Z-248 (IBM PC-AT compatible)
EGA Enhanced Graphics Adapter (Quadram QuadEGA and
Zenith Z-449)
ECD Enhanced Color Display (Princeton HX-12E)
80287 math coprocessor
Zenith Z-248 (IBM PC-AT compatible)
VGA Video Graphics Aray (Paradise VGA Professional)
Monochrome Display (Zenith ZVM-1240)
No math coprocessor
Zenith Z-181 and Z-183 Laptop Computers
Internal CGA Color Graphics Adapter
Internal Twisted-Crystal Display
No math coprocessor
Zenith Z-151 (IBM PC-XT compatible)
Standard CGA/Composite Color Graphics Adapter
Monochrome Monitor (Zenith ZVM-1230A)
Color Monitor (Mitsubishi CS-2061R)
8087 math coprocessor
Zenith Z-148 (IBM PC-XT compatible)
Internal CGA Color Graphics Adapter
RGBI Color Monitor
No math coprocessor
Several users have also reported successful operation on
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 8
other systems including an IBM PS/2 Model 80 and a Compaq Model
386/20. The program has also been tested on various "IBM-clone"
systems with numerous variations including CGA/EGA/VGA Graphics
Adapters and Hercules Graphics Adapters (HGC). The only problem
encountered was with a 101-key keyboard emulator (supplied by
Microsoft!) which caused the system to hang when ASTROCLK was
executed; a reboot was required to resume operation. When the
emulator program was removed, ASTROCLK executed without
difficulty.
Several ASTROCLK functions use the QuickBASIC SHELL command
to execute DOS commands directly or to return the user to a
secondary command processor (Function Key F9). All of my systems
use MS-DOS Version 3.1 or higher but I have read reports that
the QuickBASIC SHELL does not operate correctly for versions of
MS-DOS or PC-DOS of 3.0 or lower. I recommend that you upgrade to
Version 3.2 or higher for better system performance in general
and to avoid problems with the SHELL command in particular.
ASTROCLK supports the EGA 43-line mode to a limited extent:
if the system is in that mode at program startup, it will return
to that mode upon final exit. I'm rather fond of the EGA's 35-
line mode and often use it in preference to either 25- or 43-line
modes. Unfortunately for me, QuickBASIC (any version) refuses to
recognize the 35-line mode on entry and returns the system to the
25-line mode upon exit. Regardless of the screen mode detected at
the start of execution, ASTROCLK always sets the system to 80
columns and 25 lines for maximum compatibility and ease of
viewing.
The "/M" command line option (see PROGRAM OPERATION, below)
is recommended for systems equipped with a monochrome display
adapter and monochrome monitor. It also forces monochrome display
on computers which have CGA-compatible video adapters but
simulate colors with shades of gray or varying intensities of a
single color, such as the Zenith Z-181 and Z-183; these computers
otherwise require some adjusting to see the shades of blue,
especially bright white on green background (used for LOCAL
COORDINATES and HELP screens). The green monochrome monitor on my
Z-151, on the other hand, rendered all colors visible. Results
will obviously vary from system to system. Limited tests have
been performed on systems equipped with a monochrome video
adapter using the "/M" command line option and the program
performed properly.
The performance of different computers varies considerably,
the single most important factor being the presence or absence of
a math coprocessor. Program ASTROCLK uses the double precision
floating point format for almost all significant calculations,
and the added performance of the coprocessor is significant.
Without it, even an AT-class computer has perceptible delays in
the Precision Time and Data Displays; with it, an old PC-class
computer easily completes the same tasks within one second. To
measure the performance under these conditions, a special version
of program ASTROCLK was prepared to time the nutation and
obliquity of the ecliptic calculations required for the
computation of Apparent Sidereal Time. The following table shows
the results of the tests on several different computer
configurations ranging from a PC/AT-compatible to my oldest
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 9
machine, a PC/XT-compatible. For comparison, the Norton Utilities
System Information Computing Index (SI) is shown. Computation
time only is measured for a single iteration of the calculations
(8825) and for the average of ten interations (8826A). Unless
otherwise noted: the compiled version of ASTROCLK was used; all
computers were running MS-DOS Version 3.1 or higher; all computer
models are Zenith part numbers; and, all times are in seconds and
are typical except clock speed is in MHz. The math coprocessor is
not the only factor in execution speed; significant software
improvements were made in Version 8826A as compared to Version
8825. The times for both versions are shown for comparison. (Not
all system configurations were available for testing Version
8826A.)
CPU/COPROCESSOR PERFORMANCE COMPARISONS
---------------------------------------
8825 8826A
MODEL CLOCK CPU COPRO TIME TIME** SI
---------------------------------------------------------
Z-386 16.00 80386 ----- 0.88 0.07
Z-248 8.00 80286 80287 0.38* 9.0
Z-248 8.00 80286 80287 0.27 0.015 9.0
Z-248 8.00 80286 ----- 1.65 9.0
Z-183 4.77 80C88 ----- 9.35 0.87 1.0
Z-183 8.00 80C88 ----- 6.59 0.60 1.6
Z-151 4.77 V-20 8087 0.60 0.03 1.8
Z-148 4.77 8088 ----- 9.35 0.85 1.0
Z-148 8.00 8088 ----- 5.48 0.51 1.7
* QuickBASIC interpretive mode
** Average of 10 iterations of calculations
All machines performed "normal" calculations without undue
delay. The various clock displays were updated every second and
only in the Target Tracking Display, Precision Time and Data
Displays, and the Planetary Data Displays (modes 0, 8 and 9) were
computational times very noticeable; slower machines, especially
any machine without a math coprocessor, required from 2 to 5
seconds to update the calculations depending upon the mode.
Planetary position calculations, being the most complex, require
the most computational time and involve the greatest delays.
I have not tested the minimum memory requirements for
ASTROCLK. All of my systems are equipped with 640K. As of Version
8907, the program requires more than 200K bytes of memory and
probably WILL NOT execute in a minimum 256K system. Since
ASTROCLK can invoke QuickBASIC's SHELL command to return you
temporarily to DOS with ASTROCLK still in memory, I recommend the
use of 640K memory. However, even with 640K of memory, the fact
that ASTROCLK is resident means that programs which require a
great deal of memory may fail to execute properly under the
shell. These programs must be executed outside ASTROCLK.
Comments and test results from other system configurations
are welcome. Note that future versions of ASTROCLK may require
additional memory and/or disk space.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 10
PROGRAM OPERATION
This section describes the operation of program ASTROCLK,
including required files, starting the program, and initial
operations.
Required ASTROCLK Files
Program ASTROCLK is normally distributed in archived form
and includes the following files:
ASTROCLK.EXE Executable ASTROCLK program
ASTROHLP.EXE Executable ASTROHLP program
ASTROCLK.BAS Main ASTROCLK source for QB4
ASTROCLK.CAT Data file of additional stars
ASTROCLK.CTY Data file of cities/locations
ASTROCLK.DC1 ASTROCLK Documentation, Part I
ASTROCLK.DC2 ASTROCLK Documentation, Part II
ASTROCLK.HST Revision history for ASTROCLK
ASTROCLK.INI * Data file for initialization
ASTROCLK.MAK Source module list for QB4
ASTROCLK.MPC Minor Planet Catalog
ASTROCLK.PIF PIF file for Microsoft WINDOWS
ASTROFNT.COM EGA Soft Font (EXPERIMENTAL)
ASTROHLP.BAS Program source for ASTROHLP, QB4
ASTROSB1.BAS SUB/PROCEDURE source for QB4, 1/3
ASTROSB2.BAS SUB/PROCEDURE source for QB4, 2/3
ASTROSB3.BAS SUB/PROCEDURE source for QB4, 3/3
MESSIER.CAT Data file of Messier objects only
READ.ME * Latest information/changes
USCITIES.CTY 718 U. S. city coordinates
* May not be present in archived files
Program ASTROCLK if often distributed via bulletin board
systems and on disk as three compressed files. A complete version
should contain ALL of the listed files except as noted. Depending
upon the source, different file compression programs may be
required to unpack the files; the required program is usually
indicated by the filetype of the archived files.
Only the files ASTROCLK.EXE and ASTROHLP.EXE are required
for operation of the program. If necessary, file ASTROHLP.EXE may
be omitted but the on-screen help functions will not operate and
no warning message will be given.
File ASTROCLK.CTY adds the capability to read the location
of various U. S. and Canadian cities; a warning message is
displayed if it is not present and a search of the file is
attempted. File ASTROCLK.CAT contains data for 1645 stars and
galaxies which may be requested by name or number; a warning
message is displayed if the file is not present and a catalog
search is requested. File ASTROCLK.INI is not normally included;
it is quite small and will be created automatically. File
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 11
ASTROCLK.PIF allows the program to be run under Microsoft WINDOWS
if sufficient memory is available; it has been tested with
Version 2.03. File READ.ME contains recent information or changes
not described in this file and may or may not be included.
An additional catalog file, MESSIER.CAT, contains data for
the 109 Messier objects which has been extracted from file
ASTROCLK.CAT, for convenience in locating these objects. An
additional city file, USCITIES.CTY contains coordinates for 718
U. S. cities to higher accuracy than file ASTROCLK.CTY.
Beginning with Version 8908, ASTROCLK can also process and
track minor planets, comets, and asteroids. File ASTROCLK.MPC is
an external binary catalog containing the first 250 minor planets
which may be selected by Minor Planet Number or Name. The binary
catalog has been prepared with my program MPCAT, developed for
this purpose, using data compiled by E. G. Bowell of the Lowell
Observatory and provided by Ed Tedesco of the Jet Propulsion
Laboratory. The full minor planet catalog, EPHEM891.MPC with
3,774 minor planets, comets, and asteroids, is available
separately from my bulletin board system. New updated minor
planet catalogs are released at approximately six month
intervals. These versions of the minor planet data have been
converted into the binary format expected by ASTROCLK using
program MPCAT; as with program ASTROCLK, the current version of
MPCAT and the source are always available from my bulletin board
system (BBS). See the section A BRIEF EDITORIAL for more
information on the BBS.
As an experiment for EGA users, file ASTROFNT.COM provides
an alternate screen font. The screen typeface is changed from its
normal appearance to a cleaner typeface resembling Helvetica. To
use this screen font, enter "ASTROFNT" prior to executing program
ASTROCLK (the cursor may disappear but don't worry!) or press the
letter "E" during normal operation. CAUTION: Use of ASTROFNT with
other display adapters may produce unpredictable results!
ASTROCLK is written and compiled using Microsoft QuickBASIC,
Version 4.50. Source files ASTROCLK.BAS, ASTROSB1.BAS,
ASTROSB2.BAS, and ASTROSB3.BAS are all required for use with the
compiler. In addition, ASTROCLK.MAK is required for use in the
interpreter mode. Although I normally compile and link from
within QuickBASIC, the following batch file may be used to
compile and link ASTROCLK to produce a stand-alone .EXE file (all
files assumed in the current drive and directory):
bc astroclk/e/x/o/t/c:512;
bc astrosb1/o/t/c:512;
bc astrosb2/o/t/c:512;
bc astrosb3/o/t/c:512;
link /ex astroclk+astrosb1+astrosb2+astrosb3,astroclk.exe;
Note that the compile and link commands may be particular to the
versions of BC and LINK being used, Version 4.50 and Version 3.69
respectively in this case. See A BRIEF EDITORIAL near the end of
this document for information on how to obtain the most recent
version of all ASTROCLK files.
Users who require minimum size run files because of memory
constraints may choose to compile and link ASTROCLK to use
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 12
Microsoft's runtime module, BRUN45.EXE, instead of generating a
standalone program. Approximately 40K less RAM memory is required
for ASTROCLK in this configuration. However, this configuration
is less flexible with respect to starting directory: BRUN45.EXE
must be in the same directory as ASTROCLK.EXE, and ASTROCLK must
be run from that directory. Batch files which work correctly with
the standalone version may have to be modified.
Beginning with Version 8933, the help functions for ASTROCLK
were removed to a separate program, ASTROHLP.EXE, automatically
executed by Function Key F1. The source file for help is
ASTROHLP.BAS. This change reduced the size of the main ASTROCLK
program by 10K bytes and reduced the RAM memory requirements by
about the same amount, but subsequent versions have more than
used up the memory again.
Starting Program ASTROCLK
To start ASTROCLK, first verify that your computer is set to
the correct local time and date using the TIME and DATE commands,
then enter one of the following commands at the DOS prompt:
ASTROCLK [for all COLOR monitors]
ASTROCLK /M [for MONOCHROME monitors]
ASTROCLK /R [to force RED on color monitors]
ASTROCLK /G [to force GREEN on color monitors]
followed by RETURN (or ENTER, which I will call RETURN) and the
program will begin execution. The descriptions and examples in
this documentation assume you are using a color monitor; if you
are using a monochrome monitor, ignore all references to colors.
However, all users should note that negative years, described as
RED in this documentation, will BLINK in the program's date
windows when the "/M" option is used or when either of the single
color program modes is set; the UTC Julian Date window, of
course, will show the correct number for all dates.
Using one of the command line color options forces the
program to that color mode immediately and overrides any prior
color mode. When a color option is NOT used, ASTROCLK will
initially display its signon screen in full color (for color
monitors); using the "/R" or "/G" color option will use the
selected color for the signon screen as well as all subsequent
operations. This is particularly useful with the RED option to
protect night vision when alternating between ASTROCLK and other
programs. ASTROCLK may also be switched between the monochrome,
color, red, and green modes during execution using Function Key
ALT-F10. See the section SETTING PROGRAM OPTIONS for further
information.
As initially configured, ASTROCLK assumes that the all data
files are in the current drive and directory. If this is not the
case, you may include the drive and path for the various ASTROCLK
data files using the following command pattern (note space after
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 13
ASTROCLK):
ASTROCLK [drive:][\path][coloroption]
"drive:" must be a single letter followed by a colon and must
correspond to a valid drive. If no path is included, ASTROCLK
assumes the current directory on the specified drive or, if no
drive is included, on the current drive. If the path is included,
it must begin with the backslash, "\", and the path must exist.
See your DOS manual for an explanation of paths and directories.
If present, the color option must follow the drive and/or
path; only ONE of the color options /M, /R, or /G may be used to
force MONOCHROME, RED or GREEN respectively. Using a color option
will override any prior color setting saved in file ASTROCLK.INI.
If no color option is included on the command line, ASTROCLK will
start in full color, then read the file ASTROCLK.INI (if present)
and set the color to the mode last used.
For example, if all data files are on disk drive B: in
subdirectory ASTROCLK and you want to force monochrome display,
the following command should be used:
ASTROCLK B:\ASTROCLK/M
********************
* IMPORTANT NOTE *
********************
Once ASTROCLK has been executed the first time, the drive
and path information are saved in the program initialization
file ASTROCLK.INI. Thereafter, ASTROCLK uses the information
in ASTROCLK.INI and overrides any drive or path specification
entered on the command line. However, the command line color
options (/M, /R, or /G), if present, will take precedence over
the previous color saved in the file. Use Function Key ALT-F10 to
change the drive and/or subdirectory from within ASTROCLK, or
delete file ASTROCLK.INI at the DOS prompt to start over. See the
section SETTING PROGRAM OPTIONS for additional information.
* * * * *
Running Program ASTROCLK
When ASTROCLK begins, a title screen will appear and the
program will perform various initialization tasks. After a few
seconds ASTROCLK will display the Local Standard Time (or
Daylight Time if it has previously been set using the DAYLIGHT
FLAG entry with Function Key ALT-F10) in the main display window
and all clocks will be running. For time zones in the United
States, the correct zone name will be displayed.
The program reads your DOS software clock for the current
time and date; set your system clock accurately before you run
ASTROCLK using your hardware clock if your computer has one or
using the TIME and DATE commands if not. If your version of
MS-DOS includes the program RTCLOCK (supplied with Zenith 80286,
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 14
80386, and laptop computers), you may use ALT-F3 to set the
system clock from the internal hardware clock. If the program to
read your hardware clock has a different name, create a batch
file named RTCLOCK.BAT which includes the required command(s),
make sure it can be located via the PATH command, and then you
may use ALT-F3 to update the software clock.
For example, my Zenith Z-151 includes a special (non-Zenith)
hardware clock which requires a program called RDCLOCK to set the
software clock from the hardware clock. I reset the software
clock using the following command in a batch file called
RTCLOCK.BAT:
RDCLOCK >NUL
This reads the hardware clock, sets the software clock, and sends
its screen output to the "bit bucket" (throws it away to a
special DOS device called "NUL") so that it does not disturb my
ASTROCLK display.
I have also noticed that for some systems the software clock
is not set properly when the system boots but is slow by some
five or ten seconds. This may be a peculiarity of the Zenith MS-
DOS 3.2x software being used on the system in question, but
apparently the computer reads the hardware clock at some point
during the boot process, then does something which suspends the
clock before it turns the system over to me. I have solved the
problem by inserting the RTCLOCK command near the end of my
AUTOEXEC.BAT file. Now the software clock is set again after all
of the odds and ends have been gotten out of the way.
If you do not have a program which reads your hardware clock,
or if you do not have a hardware clock, you can exit temporarily
back to DOS using Function Key F9 to set or reset the time and/or
date with the DOS TIME and DATE commands. Then enter EXIT to
return to ASTROCLK.
It is also possible to "fool" ASTROCLK by setting the DOS
system clock to any desired date and time. However, because of an
internal DOS software limitation, the DOS clock may only be set
for years from 1980 through 2199; in general, I recommend that
you use ASTROCLK's SIMULATION mode of operation for non-current
dates.
*************
* CAUTION *
*************
Beginning with DOS Version 3.3, the DOS DATE and TIME
commands may set BOTH the software AND the hardware
clocks for most AT-class and 386-class computers as
well as some others. Therefore, do NOT use the DOS DATE
and TIME commands with DOS Version 3.3 and higher if
you wish to preserve the setting of the hardware clock.
The program automatically presets the celestial coordinates
for the star POLARIS (Alpha Ursae Minoris), the first and
brightest star of the constellation Ursa Minor (Little Bear).
POLARIS is commonly referred to as the pole star because of its
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 15
close proximity to the celestial (and geographical) North Pole.
As a result, it has long been used for navigation and the
alignment of astronomical instruments. More recently, it is often
used to align satellite dishes.
Since I don't know where you live, the program starts out
with the geographical coordinates for Rancho Palos Verdes,
California, near Los Angeles. These coordinates are displayed in
the lower left portion of the screen. However, in order to use
the sidereal time and celestial tracking features for your own
location, you need to know your local longitude (West is
negative) and latitude (South is negative).
Goode's World Atlas, 17th Edition, (see BIBLIOGRAPHY) is an
ideal reference for this purpose; the Index contains some 30,000
cities and other locations worldwide along with their
geographical coordinates to a precision of one minute. While I
cannot vouch for the accuracy of the data, Goode's is the only
atlas I know with this information, a new feature with the 17th
Edition. With a little care, your local coordinates can also be
interpolated to an accuracy of about ten minutes of arc using a
good, detailed road map provided the map includes the fiducial
marks for longitude and latitude.
Use Function Key F6 to input your local coordinates and
local place name; see also the section SETTING LOCAL COORDINATES
for a listing of the coordinates of selected cities in the United
States and Canada. If your location is near one of the these
cities, the coordinates can be read directly from file
ASTROCLK.CTY. The file is in standard ASCII code, and may be
edited to include additional cities and locations using any
editor provided the proper format is observed; WordStar and other
word processor users, use the ASCII or "Non-document" mode.
Both geographical and celestial data can be entered (and
displayed) in several different formats. Celestial coordinates
may be entered or displayed as degrees plus decimal degrees,
degrees plus minutes and decimal minutes, or degrees plus minutes
plus seconds and decimal seconds. All of these methods are
acceptable to ASTROCLK although the separator varies (colon or
comma for times, comma for degrees and dates).
* * * * *
EUROPEAN USERS PLEASE NOTE
Both in this documentation and in program ASTROCLK itself,
the period (point, ".") is used for the decimal point to separate
the integer and fractional parts of a number rather than the
comma (virgule, ",") as is the practice in many European
countries. This usage is sufficiently deeply buried in the
software that it is impractical to make it dynamically
configurable. American users have to contend with dates entered
in the European style (DD,MM,YYYY), so I've managed to make
things a little inconvenient for everyone!
Egalement ici dans cette texte et en le programme ASTROCLK,
le point (".") plutot que la virgule (",") est utilize pour
separer les deux parties d'un nombre, le nombre entier et le
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 16
fragment. C'est usage commun ici aux Etats Unis. Domage, mais il
faut que les Americains utilizent les dats comme les Europeennes
(jour, mois, ans). C'est dificile pour tous le monde! [Traduction
grace a Dictionnaire Larousse, moins les accents.]
* * * * *
When ASTROCLK first starts, the current Local Standard Time
is displayed in the main window in large numerals. The number
keys 0 through 9 (on the top row of the keyboard) and several
other keys select the display mode for the main window:
1 LST/LDT Local Standard/Daylight Time
2 UTC Coordinated Universal Time
3 LMST Local Mean Sidereal Time
4 GMST Greenwich Mean Sidereal Time
5 TDT/ET Terrestrial Dynamical/Ephemeris Time
6 Perpetual Calendar
7 Additional Date Information
8 Precision Time and Data Displays
9 Planetary Data Displays
0 Celestial Tracking Display
T Interval Timer Display
A Alarm Countdown Display [if Alarm is set]
Function Key F1 gives quick help for the function keys, but
should not be considered a substitute for this documentation.
Using Function Key F7, the information displayed on the
Target Tracking Display at the left of the screen can be switched
between several formats including whole units (hours or degrees
as the case may be) plus decimal units, or a more conventional
display (hours, minutes, seconds or degrees, minutes, seconds).
Pressing ALT-F7 will change the Target Tracking Display
coordinates from Right Ascension (hours) to Sidereal Hour Angle
(degrees) and Hour Angle (hours) to Greenwich Hour Angle
(degrees), forms preferred by navigators.
With the exception of the Julian Date (which is displayed to
six decimal places), the running clocks are displayed to the
nearest second. Other data are displayed to 0.000001 degrees or
hours, 0.0001 minutes of time or arc, or to 0.01 seconds of time
or arc, depending upon the display format selected with Function
Key F7. The Precision Time Display (Display Mode 8) gives various
time information to a precision (and approximate accuracy) of
0.0001 seconds. Most internal calculations are made in
QuickBASIC's DOUBLE PRECISION data format to yield maximum
accuracy and precision, but not all data are necessarily accurate
to the precision displayed. See the section PRECISION AND
ACCURACY TESTS for additional information.
When the clocks are ON, ASTROCLK checks the system time and
attempts to begin a new set of calculations each second. Since
these calculations tend to be complex and time consuming, some
slower computers may not finish the task within the allotted
time. My Zenith Z-183 laptop, running at 8 MHz but with no math
coprocessor, skips every third or fourth second when operating in
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 17
the Target Tracking Mode and the Precision Time and Data
Displays. This does not affect the accuracy of the displayed
data, only the frequency with which it is updated. For
comparison, my old Zenith Z-151 running at 4.77 MHz but with an
8087 math coprocessor, manages to keep up just fine. Regardless
of the computer type, a math coprocessor will substantially
decrease computation times. See the performance comparisons in
the section HARDWARE REQUIREMENTS. Version 4.50 of Microsoft's
QuickBASIC, the programming language used for ASTROCLK,
automatically senses the presence of a math coprocessor and uses
it if it is available.
To exit ASTROCLK, press ESC and you will return to the DOS
prompt. ASTROCLK always rewrites the file ASTROCLK.INI prior to
exit in order to reflect the current coordinates, flags, display
modes and other information. Each time ASTROCLK is started it
checks for file ASTROCLK.INI and reads its contents if present.
If you change the coordinates, the new coordinates will be used
the next time you run ASTROCLK.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 18
FUNCTION KEYS AND HELP
Function Key F1 invokes a HELP function which displays the
operation performed by the ten Function Keys, F1 through F10 (as
well as several ALT or SHIFT plus Function Key combinations).
While the operations are generally self explanatory, positioning
the flashing red pointer at the desired operation (F1 through
F10) with the Up or Down arrow keys and pressing RETURN will
display additional information. Pressing the desired Function Key
directly will also display the supplementary information for that
Function Key. Press RETURN (or any other key) to return to the
main HELP menu. Press the SPACE BAR to exit the main HELP menu
and return to normal program operation.
All of the displayed clocks are stopped while using HELP and
the message "Clocks OFF" will be displayed in flashing red at the
upper right of the screen. If the clocks were on when HELP was
requested, the clocks will resume normal or simulated operation
when you leave HELP and the message "Clocks ON" or "SIMULATION"
will again be displayed in green or yellow respectively at the
upper right of the screen. If the clocks were off when HELP was
requested, they will remain off when you leave HELP.
The following operations are available with the ten Function
Keys, F1 through F10:
F1 Display HELP screens. Display program name, version,
and date if pressed again when the main HELP screen is
visible.
F2 Display Target Object EPHEMERIS. Before pressing F2,
set the desired start time using F3, then select the
desired target object using F5. Press F2 and enter the
desired step interval and the number of intervals. The
ephemeris information is displayed on the screen. When
done or if more than 20 intervals are requested, the
display will pause; press any key to contiue. Use the
SHIFT-PrtSc to obtain a printed copy of the ephemeris.
F3 Set LOCAL/UT TIME and/or LOCAL/UT DATE. The on-screen
clocks are running when the time and date are set to
the system clock or when the SIMULATION mode has been
enabled with ALT-F4. (If the clocks are stopped, press
F4 to restart the clocks.) When entering time or date,
press RETURN to skip an entry and leave that item
unchanged. F3 automatically cancels the SIMULATION
mode.
LOCAL/UT/TDT TIME: Enter as Hours, Minutes, Seconds
using 24 hour notation; use either the comma or the
colon as separator. Decimal fractions are permitted for
any item. Add the letter "U" at the end of the entry to
enter UT TIME instead of local time; add the letter "T"
or "E" at the end of the entry to enter TDT/ET TIME
instead of local time.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 19
NOTE: Use ALT-F10 to set the DAYLIGHT FLAG and any
required ZONE CORRECTION. See the section SETTING
PROGRAM OPTIONS for an explanation.
LOCAL/UT DATE: Dates may be entered in a number of
formats. For "standard" dates, enter the new date in
the form DD,MM,YYYY. Note that the date is entered
European style: Day, Month, Year and that the full 4-
digit year is required. Years B.C. (Julian proleptic
calendar) are preceded by a minus sign (e.g. -4713).
NOTE: There is no year 0000 in the day numbering
algorithms used in ASTROCLK. Add the letter "U"
following the year to enter UT DATE instead of local
date. When UT TIME has been entered, UT DATE is
automatically entered rather than LOCAL DATE. Dates may
also be entered as the Julian or Sidereal date. Five
styles of day numbers may be used, selected by the
prefix used, as well as several other methods.
For a more complete explanation of time and date entry
using F3, see the section SETTING LOCAL/UT/TDT TIME AND
DATE.
Use ALT-F3 to read the hardware clock with program
RTCLOCK from within ASTROCLK. (See PROGRAM OPERATION
for details.)
Use SHIFT-F3 to set an ALARM TIME or to set the start
time for the INTERVAL TIMER. The alarm may be set up to
23 hours in advance. When set, a window appears at the
lower right of the screen and displays the set alarm
time and the time remaining in red. To set the start
time for the Interval Timer, suffix the entered time
with the letter T. To disable an already set alarm,
press SHIFT-F3 then press RETURN. See also the section
ALARM AND INTERVAL TIMER OPERATIONS for additional
information.
F4 Toggle Clocks ON or OFF. When clocks are ON, all time
and date displays are referenced to the computer's
internal software clock and any manually set local time
or date is lost. When clocks are OFF, all times on the
screen are frozen. The clocks are automatically turned
OFF if either the local time or local date is set with
Function Key F3. The message "Clocks ON" (green),
"Clocks OFF" (flashing red), or "SIMULATION" (yellow)
appears at the upper right of the screen to indicate
the current clock status.
Use ALT-F4 to toggle simulated real time. First preset
the desired time and date using Function Key F3, then
press ALT-F4 to turn on the simulation. The word
SIMULATION will appear in yellow at the upper right of
the screen (in place of the Clocks ON/OFF message) when
simulation is active. Press ALT-F4 again to disable
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 20
simulation. Function Key F3 also cancels the simulation
mode. NOTE: Unlike the DOS clock, which may only be set
for the period 1980 through 2099, the internal ASTROCLK
simulation will operate for any time and date.
Function Key F4 may be used to start and stop the
clocks in the simulation mode as usual. Function Keys
F4 and ALT-F4 stop simulated time in different ways.
When F4 is used to stop and start simulation, the
simulated time will resume as if the clocks had not
been stopped (the same as in the real time mode). Use
of ALT-F4 disables the simulation and stops the clocks;
pressing ALT-F4 again will restart simulation at the
current indicated time. If F4 is pressed after ALT-F4
has stopped simulation, normal real time operation will
follow.
F5 Set new star or celestial object TARGET COORDINATES
using either the internal star database or an external
star catalog. [NOTE: To set the target coordinates for
a planet or to use the external Minor Planet Catalog,
see the sections PLANETARY DATA DISPLAYS and MINOR
PLANET SELECTION.]
A sub-menu is displayed offering the following function
key selections:
F1 Enter the USNO Standard Navigational Star Number
(1 through 57, or 0 for Polaris) or the desired
Star Name to use the internally stored star data.
When the name is entered, upper or lower case may
be used and only sufficient letters to
unambiguously identify the star name are required.
Enter "Deneb " (with a trailing space) to
distinguish that star from "Denebola".
F2 Search for nearest USNO Standard Navigational
Star. Enter the local horizon coordinates in
degrees: ALTITUDE (the angle from the true horizon
up to the star) and AZIMUTH (the direction of the
star in the sense North=0, East=90, South=180, and
West=270). The program will search for the USNO
star closest to the position specified and the
data for that star will be displayed in the
Tracking Window.
F3 Search EXTERNAL STAR CATALOG by star name, star
identification, or catalog number. When the name
is entered, upper or lower case may be used and
only sufficient letters to unambiguously identify
the star name are required. (Enter "Deneb ", with
a trailing space, to distinguish that star from
"Denebola".) Messier objects may be identified by
common name ("ORION") or by Messier number ("M9").
If the program finds a matching entry in the
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 21
catalog, the data for that star will be displayed
in the Tracking Window; if no match can be made,
the data in the Tracking Window is left unchanged.
Press SPACE BAR to cancel the catalog search in
progress; the current data is left unchanged.
F4 Search EXTERNAL STAR CATALOG by Right Ascension
and Declination. Enter the coordinates when
requested and the program will find the catalog
stars closest to the position specified. Respond
"Y" to display the 10 closest stars or "N" to only
locate the closest star. Press RETURN to display
the star in the Target Tracking Window. Press
SPACE BAR to cancel the catalog search in
progress; the current data is left unchanged.
F5 Search EXTERNAL STAR CATALOG for nearest star.
Enter the local horizon coordinates in degrees:
ALTITUDE (the angle from the true horizon up to
the star) and AZIMUTH (the position of the star in
the sense North=0, East=90, South=180, and
West=270). The program will search the catalog for
the stars closest to the position specified. Respond
"Y" to display the 10 closest stars or "N" to only
locate the closest star. Press RETURN to display
the star in the Target Tracking Window. Press
SPACE BAR to cancel the catalog search in
progress; the current data is left unchanged.
F6 MANUAL DATA ENTRY. Enter the celestial
coordinates, Right Ascension and Declination, the
proper motion in Right Ascention and Declination
per Julian century (in seconds of time or arc),
and the object name as requested. If the proper
motion parameters are not known, press RETURN to
enter zero. If RETURN is pressed for the object
name, the display will show "Manual Target Data".
The data for the object will be displayed in the
Tracking Window.
RETURN Cancel entry of Target Coordinates, leave current
Target Coordinates unchanged, and resume normal
program operation.
When searching using local horizon coordinates,
altitude is measured in degrees up from the true
horizon; 0 degrees is the horizon and 90 degrees is
directly overhead. Don't forget to take into account
hills or other obstructions that may obscure the true
horizon. Azimuth is measured in degrees from true North
in the sense NESW; thus, 0 degrees is North, 90 degrees
is East, 180 degrees is South, and 270 degrees is West.
The star selection algorithm used in the various
searches attempts to pick the Standard Navigational
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 22
Star or external catalog star which is closest (angular
difference) to the coordinates you have entered. It may
take a little practice before you can look at the night
sky and estimate star positions accurately enough for
the program to select the correct star. While the
search is in progress, the message "SEARCHING ..." will
appear at the upper right of the screen and the clocks
will temporarily be stopped.
For an external catalog search, file ASTROCLK.CAT must
be present. This catalog includes data for 1645 stars,
Epoch J2000.0, extracted from USNO STAR1.CAT and USNO
MESSIER.CAT. Stars may be requested by catalog number
or by any of several names. See the section USING
EXTERNAL STAR CATALOGS for additional information.
While the search is in progress, the message "SEARCHING
..." will appear at the upper right of the screen and
the clocks will temporarily be stopped.
NOTE: The supplied external star catalog is a large
file, currently about 160Kb, and the search time on a
floppy disk system is rather slow; the numbers
appearing during the search indicate progress through
the catalog in increments of 50.
For manual data entry, you must know the standard
equatorial coordinates, Right Ascension and
Declination, for the celestial object you wish to
track. Star Atlases, astronomical magazines, and other
publications usually give the coordinates for objects
of interest. The input routine is very flexible and
data may be entered in a number of formats. Observe the
separator requirement: items for time (including Right
Ascension) must be separated by the colon or comma,
while items in degrees (including Declination) must be
separated by the comma. In general, only the first item
(hours or degrees) is required and a decimal fraction
is allowed for all items. If you press RETURN for an
item, the data for that item will be left unchanged.
When entering data manually, the parameters for proper
motion are requested. Press RETURN to enter zero. These
data are used by ASTROCLK to calculate the current
apparent equatorial coordinates on the Tracking Display
and are also used if the coordinates are precessed from
one epoch to another using Function Key F8. This
information is given for many stars in star catalogs
such as SKY CATALOGUE 2000.0. However, note that
ASTROCLK requires this information in SECONDS PER
JULIAN CENTURY (36525 days) and not all references use
the same units; SKY CATALOGUE 2000.0, for example, uses
SECONDS PER YEAR which must be converted prior to input
into ASTROCLK.
ALT-F5 Because of its usefulness, the coordinates of the star
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 23
POLARIS (Alpha Ursa Minoris), the pole star, are hard
coded into ASTROCLK on Function Key ALT-F5. POLARIS is
often used for navigation and for the initial alignment
of celestial telescopes and satellite dishes. Press
this key and the coordinates for POLARIS are
automatically entered and the display mode is switched
to the Target Tracking Display.
F6 Set new LOCAL COORDINATES. All entries are in degrees
and require the comma as separator between the items. A
decimal fraction is allowed for any item, and only the
first item (degrees) is required. See the section
SETTING LOCAL AND DESTINATION COORDINATES for details.
If file ASTROCLK.CTY (or an alternate city file) is
present, it may be used to read the coordinates for a
selection of cities. Enter the name of the location
desired in upper or lower case. Only letters sufficient
to uniquely identify the location are required. Press
RETURN to ACCEPT the displayed location; press SPACE to
search for the next match. Press ESC during the search
to cancel the search and leave the local coordinates
unchanged. If no match can be found, a CAUTION message
will be displayed at the lower left of the screen.
Press RETURN to continue; the local coordinates will be
left unchanged.
To enter coordinates manually, press RETURN when
prompted for the name. Then enter the LONGITUDE,
LATITUDE and ELEVATION, followed by the NAME of the
location.
NOTE: Additional city files may be available from time
to time on my BBS or by mail; see the end of the
section A BRIEF EDITORIAL for the BBS telephone number
and my address.
SHIFT-F6 Set DESTINATION COORDINATES for use with navigation
functions. Operates in all respects like F6 above
except that the destination coordinates are set rather
than the local coordinates, and you may enter "*"
instead of a name to set the DESTINATION coordinates to
the current LOCAL coordinates.
ALT-F6 Set LOCAL CONDITIONS for Elevation, Temperature, and
Pressure. Allows the user to set these conditions to
determine horizon dip and refraction. Automatic con-
version between metric and English units is performed.
F7 Set DISPLAY FORMAT for the main display window and Local
Coordinates window. When the program is started, all
angles and times on the main display window (other than
large character times) and in the Local Coordinates
window are shown in Degrees/Hours-Minutes-Seconds
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 24
format. Press F7 to cycle between display formats; the
three available formats are:
ANGLES TIMES
------------ -----------
DDD MM SS.SS HH:MM:SS.SS
DDD MM.MMMM HH:MM.MMMM
DDD.DDDDDD HH.HHHHHH
Press ALT-F7 to change Target Display coordinates from
Right Ascension (hours) to Sidereal Hour Angle
(degrees) and from Hour Angle (hours) to Greenwich Hour
Angle (degrees), preferred by navigators and given in
references such as the Astronomical Almanac. Press ALT-
F7 again to return to the original format. Declination
is not affected. See also the section TARGET TRACKING
DISPLAY for further discussion.
F8 PRECESS Internal Star Database. This function allows
the user to precess (adjust for different epochs) the
current target data and the preset star database in the
program. Upon startup, all data are set for epoch
J2000.0, the current standard epoch. Press the "Y" key
to make the precession calculations or press RETURN to
cancel the calculations and leave all data unchanged.
If you proceed, press RETURN to restore all data to
Epoch J2000.0 or enter the desired new epoch. The new
epoch may be entered in any of the following formats:
dd,mm,yyyy Calendar Date
JDnnnnnnn.nnnnnn Julian Date
DJDnnnnnn.nnnnnn Julian Date (J1900.0)
MJDnnnnnn.nnnnnn Modified Julian Date
Jyyyy.yyy Julian Epoch
Byyyy.yyy Besellian Epoch
+nnn Add nnn days to Current JD
-nnn Subtract nnn days from Cur JD
* Current Julian Date and Time
# Current Julian Date @ 0h UT
Lower case letters (yyyy, nnnnnn, etc.) represent
numbers while upper case letters (JD, J, etc.) are used
to designate the data format being used. The calendar
date method assumes the Julian or Gregorian calendar as
determined by the date and the Calendar Flag (See ALT-
F10, Setting Program Options). Except for the calendar
date method, any number of digits to the right of the
decimal point may be input although more than about six
will not be significant. Regardless of the data format
used for input, the date is internally converted to the
corresponding Julian Date for use in the precession
calculations. The current ASTROCLK internal database
epoch is always shown in the Target Tracking Display,
Display Mode 0, and in the initial Precession
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 25
instructions when using Function Key F8.
Care should be taken when manually entering data whose
epoch is different from that of the internal database.
In order to maintain consistent data within ASTROCLK,
the internal star database should first be precessed to
a data epoch, then manual data referenced to that epoch
should be entered. After that, all data may be
precessed to the final epoch; using this procedure,
both the manually entered data as well as the internal
data will always refer to the same epoch.
For example, to track a target using Epoch J2000.0
coordinates when the available catalog data is for
Epoch B1950.0, first precess the internal star data to
B1950.0 using F8, next enter the target Right
Ascension, Declination, Name from the catalog, and the
proper motion in Right Ascension and Declination (if
known) using F5 (and F6 for manual entry). Finally,
again use F8 to precess all data back to Epoch J2000.0
(or any desired epoch). Thereafter, F8 may be used as
many times as desired to precess the database.
F9 DOS SHELL. This function invokes a copy of the MS-DOS
executive, COMMAND.COM, and allows the user to enter
any legal DOS command. COMMAND.COM must be available or
ASTROCLK will ignore the request and continue normal
operation. Since COMMAND.COM must reside in available
memory in addition to ASTROCLK, use of a large RAM DISK
or TSR program may cause the DOS shell to fail. The MS-
DOS prompt is displayed and the computer performs in
most respects exactly as usual. However, far less
memory is available and therefore programs which
require very large amounts of memory for their
execution may not operate properly with the SHELL.
Enter EXIT to return to ASTROCLK and resume operation
with all data and parameters unchanged.
SHIFT-F9 may be used to automatically executa a preset
DOS command or batch file. The DOS command is set using
ALT-F10, SETTING PROGRAM OPTIONS, and is saved in file
ASTROCLK.INI. If a DOS command has been set, the
command is executed and upon completion ASTROCLK is
automatically resumed. This command has the same
restrictions and comments as the normal F9 command
above; the only difference is the execution of a preset
DOS command and automatic return to ASTROCLK. The
default is no action.
ALT-F9 may be used to automatically execute the USNO
Interactive Computer Ephemeris (ICE) or the USNO Floppy
Almanac (FA); see the section USNO EPHEMERIS PROGRAMS
for more complete information. ALT-F9 will execute the
selected USNO program if the appropriate software has
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 26
been installed in the computer AND if the appropriate
ephemeris has been selected and its path set using ALT-
F10, SETTING PROGRAM OPTIONS.
F10 Function Key F10 provides navigational calculations
using two methods: DEAD RECKONING and SIGHT REDUCTION.
For an observer in motion, ASTROCLK also calculates the
current position based upon the last "fix" and the
observer's course and speed. See the section CELESTIAL
NAVIGATION for details.
ALT-F10 is used to set or change various ASTROCLK
program options. See the following section, SETTING
PROGRAM OPTIONS, for details.
0-9 Select Display Window Mode. The system starts out with
LOCAL STANDARD/DAYLIGHT TIME displayed in large
characters. In the United States, the correct time zone
name (i.e. "PACIFIC") replaces the word "LOCAL". Press
the number key associated with each display mode to
change to that mode. (Use the numbers at the top of the
keyboard rather than the number keys on the keypad at
the right unless NUMLOCK is ON.) The available numeric
modes and alphabetic commands are:
1 Local Standard or Daylight Time (LST/LDT)
2 Coordinated Universal Time (UTC)
3 Local Mean Sidereal Time (LMST)
4 Greenwich Mean Sidereal Time (GMST)
5 Local Mean Solar Time
6 Perpetual Calendar
7 Julian Date Information
8 Precision Time Display
9 Planetary Data
0 Target Tracking Display
N Select NAVIGATION Display Mode
P Select PLANET or MINOR PLANET
(forces display mode 9 or 0)
A Alarm Countdown *
S Start/Stop Interval Timer *
T Interval Timer *
Z Stop and Reset Interval Timer *
* See the section ALARM AND INTERVAL TIMER
OPERATIONS for information on these modes.
While in display mode 0, Target Tracking, use the UP
and DOWN arrow keys to select the next or the previous
Standard Navigational Star. PgUp and PgDn increase or
decrease the selected star number by 10. Use F5 to
input a new star number directly.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 27
While in display modes 1 through 5, the large clock
displays, use the UP and DOWN arrow keys to select the
dual-time displays and the HOME key to return to
single-time display. See the section DUAL-TIME DISPLAYS
for further information.
While in display mode 6, Perpetual Calendar, use the
Left and Right arrow keys to change months, the Up and
Down arrow keys to change years, and the PgUp and PgDn
keys to change the years by decades. HOME returns the
display to the current system date. Use F3 to input a
new date or time directly.
While in display mode 8, Precision Time and Data
Displays, press PgUp or PgDn to view the next Precision
Time or Data Display. See the section PRECISION TIME
AND DATA DISPLAYS for details.
While in display mode 9, Planetary Data, use the UP and
DOWN arrow keys to change planets. See the section
PLANETARY DATA DISPLAYS for further discussion.
Pressing "N" to select the Navigation Mode Display will
result in an error message if navigation has not been
enabled with Function Key F10. See the section
NAVIGATION for further discussion.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 28
SETTING PROGRAM OPTIONS
Several ASTROCLK program options can be set using Function
Key ALT-F10. The options which can be set are: DAYLIGHT FLAG,
ZONE CORRECTION, COLOR FLAG, ICE/FA Flag, CALENDAR FLAG, external
FILE NAMES and PATHS, and PRESET DOS COMMAND. All of this
information is saved in file ASTROCLK.INI.
The DAYLIGHT FLAG determines whether or not Daylight Time is
in effect. The ZONE CORRECTION allows the user to adjust for time
zones which do not agree with the calculated values. The CALENDAR
FLAG determines which of three calendar conventions to use; it is
initially set to the Gregorian Calendar (from October, 1582). A
sub-menu is displayed when using ALT-F10 with the current values
shown enclosed by square brackets, "[...]". Press the function
key corresponding to the option you wish to change or press
RETURN to resume normal program operation with the options as
shown. A typical display showing the default values for each item
is shown below:
F1 DAYLIGHT FLAG: [OFF]
F2 ZONE CORRECTION: [0.00]
F3 COLOR FLAG: [ON]
F4 ICE/FA FLAG: [0=ICE/FA Disabled]
F5 CALENDAR FLAG: [1=Gregorian @ 1582]
F6 SET FILE NAMES & PATHS
F9 SET DOS COMMAND
(no command has been entered)
RETURN Resume normal program operation
When all changes have been made and the information
displayed on the menu is correct, press RETURN to resume normal
program operation. When you exit ASTROCLK, these options will be
saved in file ASTROCLK.INI and will automatically be restored the
next time you run the program.
Setting the DAYLIGHT FLAG
-------------------------
The DAYLIGHT FLAG selects whether or not an additional hour
will be automatically added during the time zone calculation to
determine Coordinated Universal Time. The flag applies equally to
all time zones and the window label for local time will include
the word STANDARD if the flag is OFF, or the word DAYLIGHT if the
flag is ON. For example: PACIFIC STANDARD TIME or PACIFIC
DAYLIGHT TIME. If you wish to change the state of the flag, press
Function Key F1. The DAYLIGHT flag is OFF by default. Because the
date of switching to and from daylight time are different in
different countries and are sometimes changed for one reason or
another, ASTROCLK does not automatically set the state of the
flag. If the UT TIME ZONE OFFSET has been enabled, be sure to
correct that value using F10 when the DAYLIGHT FLAG is changed.
If the DAYLIGHT FLAG is incorrectly set, all calculated
times and positions will also be incorrect. Do NOT use the
DAYLIGHT FLAG to adjust for an incorrect zone calculation; use
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 29
the ZONE CORRECTION (see the following item) for that purpose.
You may, if you prefer, leave your computer clock always set to
local STANDARD time and the DAYLIGHT FLAG always off. However,
you may NOT set your computer clock to UTC (unless you are in
that time zone); set the computer clock correctly and use display
mode 2 to view UTC instead.
Setting the ZONE CORRECTION
---------------------------
The ZONE CORRECTION allows the user to make special
adjustments in the calculation of Coordinated Universal Time
(UTC) relative to Local Time. Some time zones are not an integral
number of hours offset from UTC; in other cases the actual
standard time for a particular location is different from that
calculated by ASTROCLK because of the irregular way time zones
have been defined locally. Some countries use "Double Summer
Time" which is two hours ahead of the standard time for the zone.
To change the current ZONE CORRECTION, press F2. The correction
must be entered in hours and decimal fraction, H.HH or -H.HH, and
is automatically rounded to the nearest 0.25 hours (15 minutes);
the maximum correction is restricted to the range -2.00 hours to
+2.00 hours. The ZONE CORRECTION is calculated in ADDITION to the
DAYLIGHT FLAG.
IMPORTANT NOTE: Unlike the Daylight Flag, which remains
unchanged when you change local coordinates, the Zone Correction
will be reset to 0.00 hours any time you change the local
coordinates on the assumption that the Zone Correction is
unique to a given location. This also assures that when using
the external city file to change cities and load the coordinates
from the file, the Zone Correction will be reset. The default
value for the Zone Correction is 0.00 hours.
Setting the COLOR FLAG
----------------------
The COLOR FLAG allows you to switch between color, red,
green, and monochrome display. The COLOR mode uses various colors
for the display. The RED option sets all screen colors to red in
order to protect night vision if the computer is operated in a
darkened area. The GREEN option sets all screen colors to green;
this may help reduce eye fatigue during extended use. The OFF
(monochrome) mode is useful if you wish monochrome display or
white display on color monitors. Switching to any of the color
modes on some true monochrome systems may cause an error. See
also the section PROGRAM OPERATION for additional information on
the command line color options.
To change the COLOR FLAG from one mode to the next, press
Function Key F3; the color changes for the new mode will take
effect immediately within the window but the balance of the
display will not be affected until you leave the Setting Programs
Options window by pressing the RETURN key.
The state of the COLOR FLAG is saved in file ASTROCLK.INI
and the program will use the previously set color mode the next
time it is run. However, the command line color option (/M, /R,
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 30
or /G), if present, always overrides the saved state of the COLOR
FLAG read from file ASTROCLK.INI.
Setting the ICE/FA FLAG
-----------------------
The ICE/FA FLAG allows you to select between the following
three options for external USNO ephemeris programs:
0 = No external USNO ephemeris program is available.
Pressing ALT-F9 will display an error message.
(DEFAULT)
1 = The USNO Interactive Computer Ephemeris, ICE, is
installed and will be executed by pressing ALT-F9. Be
sure to set the ICE drive and/or path correctly!
2 = The USNO Floppy Almanac, FA, is installed and will be
executed by pressing ALT-F9. Be sure to set the FA
drive and/or path correctly!
Press F4 until the desired option is displayed. Do not
select one of the USNO ephemeris program options unless the
appropriate ephemeris files have been installed. See also the
section USNO EPHEMERIS PROGRAMS for additional information.
Setting the CALENDAR FLAG
-------------------------
The CALENDAR FLAG allows you to select between the following
three calendar conventions:
0 = Strict Julian Calandar for ALL dates. Technically, this
calendar is known as the Julian Proleptic Calendar for
dates prior to 46 B.C. NOTE: The Julian Calendar may
not be used in real time (see below).
1 = Julian Calendar switching to Gregorian Calendar in
October, 1582 in accordance with standard astronomical
convention (DEFAULT).
2 = Julian Calendar switching to Gregorian Calendar in
September, 1752 corresponding to usage in Great Britain
and her colonies (including the United States).
Press F5 to change the flag until the desired calendar
convention is displayed. For additional information on the
various calendar conventions, see the section DATES AND THE
GREGORIAN CALENDAR.
NOTE: Regardless of the calendar convention in effect,
ASTROCLK always assumes that the system clock is set to the
correct date. This means that only calendar flag values of 1 and
2 are permitted with the CLOCKS ON. ASTROCLK's internal date
functions are performed using the current Julian Date. Therefore,
switching from the Gregorian Calendar to the Julian Calendar for
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 31
a modern date with the CLOCKS OFF will leave the Julian Date
unchanged but will change the calendar date to a new value,
correct for the strict Julian Calendar. However, if the clocks
are ON, they will automatically be set to OFF and a warning
message will be displayed. If you wish to use the program with
the Julian Calendar and the clocks running, use the SIMULATION
mode.
Setting the FILE NAMES and PATHS
--------------------------------
In order to execute the help function and to utilize the
external data files and the USNO Interactive Computer Ephemeris
(ICE) or Floppy Almanac (FA), ASTROCLK must know what the file
names are and where to find them. The default condition is that
these files are all located in the current directory and that the
files have the following names:
ASTROHLP.EXE External Help Program
ASTROCLK.CAT External star catalog
ASTROCLK.MPC External minor planet catalog
ASTROCLK.CTY External city file
ICE.EXE USNO Interactive Computer Ephemeris
FAnn.EXE USNO Floppy Almanac (nn=88-99)
There is a different file for each year for the USNO Floppy
Almanac. All files required by ICE or FA must be located in the
same directory as the .EXE file. A common drive and path may be
specified in the command line when starting ASTROCLK for the
first time.
********************
* IMPORTANT NOTE *
********************
Once ASTROCLK has been executed the first time, the drive
and path information are saved in the program initialization
file ASTROCLK.INI. Thereafter, ASTROCLK uses the information
in ASTROCLK.INI and overrides any drive or path specification
entered on the command line. You may use ALT-F10 and then F6 to
change the drive and/or subdirectory from within ASTROCLK, or you
may delete file ASTROCLK.INI at the DOS prompt to start over.
* * * * *
Since two of the external data files, ASTROCLK.CAT and
ASTROCLK.CTY, are conventional ASCII files which may be edited by
the user, a provision is included here to permit the user to
specify an alternate file name for either of these files,
including drive and path. For example, you might wish to use a
special city file when traveling in Europe. More ambitious users
may wish to prepare their own external star catalogs.
The current STAR CATALOG, MINOR PLANET CATALOG, and CITY
FILE names are shown on the menu, in that order. If a drive
and/or path was specified with the command line, they will also
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 32
be shown. If no drive or path is shown, ASTROCLK assumes the
current drive and directory. To change one or more file names,
press F6 and enter the new name when prompted or press RETURN to
leave a name unchanged. You may include a drive and path
specification if desired. Enter SPACE to restore the file name to
the default. (A long path specification may exceed the width of
the display window but it will be processed correctly.)
For convenience, an additional file, MESSIER.CAT, is
available with the data for the 109 Messier objects only. The
same data is included in file ASTROCLK.CAT but at the end of that
long file. If you are content with the 57 internal USNO stars
plus Polaris and just wish to add the Messier objects, use
MESSIER.CAT and then substitute it for ASTROCLK.CAT using ALT-F10
and then F6. This will substantially reduce the catalog search
time, especially on floppy disk based systems. M40 has always
been missing and the entry for that item contains only null data.
An alternate city file, USCITIES.CTY is available which
includes some 718 U.S. cities with the geographical coordinates
given to a higher accuracy than the standard ASTROCLK.CTY.
Other special city files and star catalogs may also be
available from time to time on my Bulletin Board System (BBS).
See the section A BRIEF EDITORIAL near the end of this document
for information on the BBS.
THE "EASY" METHOD OF SETTING PATHS: If you do not understand
paths and subdirectories or simply do not wish to alter
ASTROCLK's default setup, simply make sure that all ASTROCLK
files (and the USNO ICE or FA files, if you have them) are
located on the same drive and directory. I recommend that the
files be located on the selected drive in directory ASTROCLK; see
your DOS manual for information on how to create the directory
and copy the ASTROCLK files to that directory. Then run ASTROCLK
from the ASTROCLK directory using the following command (which
assumes drive C:):
ASTROCLK C:\ASTROCLK
All drive and path information will be saved in file ASTROCLK.INI
for subsequent uses of the program. Then, if you execute ASTROCLK
from the ASTROCLK directory, the program will be able to find all
its required files.
However, it is often necessary or convenient to have some
files, especially the Floppy Almanac files, located in another
drive and/or subdirectory. This is particularly true for floppy
disk based systems where the individual disk capacity may prevent
all files from being on the same disk. The drive and path for
ASTROCLK and for the USNO Interactive Computer Ephemeris (ICE) or
Floppy Almanac (FA) may be separately set using F6, and specific
file names (including drive and directory if desired) may be set
for the external star catalog, minor planet catalog, and city
files.
When setting the ASTROCLK and ICE or FA paths, ONLY THE
DRIVE AND PATH ARE SPECIFIED. A backslash ("\") should be the
first character of each path except for a blank path; a CAUTION
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 33
warning message will be displayed if you do not include it. Do
NOT add a backslash at the end of the path. Unless you include a
drive specification such as "D:", ASTROCLK assumes that all files
are located on the current drive. If you include a drive
specification with the ICE or FA path, you must also include a
drive specification with the ASTROCLK path; a CAUTION warning
message will be displayed if you do not include it.
Thus, if your ICE/FA and related files are in drive
D: and path \FA, enter "D:\FA", followed by RETURN, for the
ICE/FA path. Setting the ICE/FA path not only enables ASTROCLK to
locate the ICE.EXE or FAnn.EXE files, it also tells ASTROCLK
where to write the file ICE.DFT or FA.DFT (which determines the
default conditions for the program).
The external file names default to ASTROCLK.CAT,
ASTROCLK.MPC and ASTROCLK.CTY, and ASTROCLK also assumes by
default that they are all located in the ASTROCLK path. Enter an
alternate file name for one or more files if desired. You may
include the drive and/or subdirectory if they are different from
ASTROCLK's values. Enter a SPACE to reset the file name to the
default name.
Setting the PRESET DOS COMMAND
------------------------------
This feature, requested by several users, allows you to
enter a preset DOS command which will be executed from ASTROCLK
each time you press SHIFT-F9. The current preset DOS command is
shown on the screen; if no command has been entered or read from
file ASTROCLK.INI, the following message will appear:
(no command has been entered)
Press F9 to select this option and then enter the desired command
or the name of the batch file (without the .BAT portion of the
file name) which you wish to be executed. Press RETURN by itself
to clear the preset DOS command. NOTE: If you select this option
by mistake, you must re-enter the desired DOS command or it will
be cleared.
Once the desired DOS command has been entered, return to
ASTROCLK and test the command by pressing SHIFT-F9. Bear in mind
that very large programs may require more memory than is
available under the SHELL used by ASTROCLK to execute DOS
programs. Further, using TSR (Terminate and Stay Resident)
programs may leave insufficient memory to use this feature or may
cause programs to operate unpredictably.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 34
SETTING LOCAL/UT/TDT TIME AND DATE
ASTROCLK has three basic modes of operation: real time,
simulated real time, and static. In the real time mode, the
clocks are running synchronized to the system clock and the data
displayed are calculated every second (computer calculation time
permitting). The simulation mode is the same as real time except
that ASTROCLK uses a time previously set with Function Key F3 as
its reference. Using a Zenith Z-183 laptop computer not equipped
with a coprocessor, ASTROCLK is able to make most calculations
(except for Tracking and Precision data) within one second.
Compared to a Zenith Z-248 8 MHz AT-compatible computer with a
math coprocessor, the computational delays are noticeable.
Provided the local time, date and coordinates have been properly
set, the data reflect the correct real time (or simulated real
time) parameters. In the static mode, the data are held at the
values for the specified time.
Except in the Navigation Mode, an algorithm is used to
automatically calculate the time offset from UTC, Coordinated
Universal Time based upon the longitude of the local coordinates.
UTC is roughly equal to Greenwich Mean Time (GMT) for years 1925
and later. The results of this calculation are shown as UTC ZONE
(for example, -118 degrees yields UTC -8.0 for Pacific Standard
Time in Southern California), and are used in all subsequent time
and position calculations. All calculations are based upon
Standard Time. If Daylight Time is in use AND your computer clock
is set to Daylight Time, use Function Key ALT-F10, SETTING
PROGRAM OPTIONS, and set the DAYLIGHT FLAG ON to automatically
adjust the times. To return to Standard Time, set the DAYLIGHT
FLAG OFF. ASTROCLK does not perform any date tests to verify the
validity of the DAYLIGHT FLAG setting.
Because of the strange ways time zones have been drawn, the
automatic time zone calculation may not always produce the
desired result. The calculated time IS the correct time based
upon the division of the world into 24 equal time zones. However,
for political reasons or for local convenience, time zones often
do not excatly follow the designated meridians. If a location is
more than 7-1/2 degrees East or West of the 15 degree meridian
corresponding to the local standard time, the time calculations
will be an hour in error. Use the ZONE CORRECTION with ALT-F10,
SETTING PROGRAM OPTIONS, to correct for this problem to the
nearest fifteen minutes. Some time zones are not set at an
integral number of hours offset from UTC, fortunately none of
them in the United States. A correction of from -2.00 hours to
+2.00 hours will be accepted in order to accommodate both time
zone errors and double daylight times. For U.S. locations not
requiring this special correction, ASTROCLK will automatically
display the correct zone name, Eastern, Pacific, etc.
In the Navigation Mode, the calculation of times is handled
slightly differently. Because the computer may move from one time
zone to another, the Navigation Mode requires that the UT TIME
ZONE OFFSET, the difference between the computer's clock and
Universal Time (UT), be entered using Function Key F10. ASTROCLK
then automatically converts the computer clock to UT before
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 35
making adjustments for the current longitude (whether calculated
or manually entered). This permits the computer to move freely
from time zone to time zone without resetting the computer's
internal clock. However, there is as usual no free lunch; because
the local time is strictly dependent upon the current longitude,
no ZONE CORRECTION for time zones which do not correspond to the
calculated time is permitted. Any ZONE CORRECTION in effect when
the UT OFFSET is set will be cleared. On the other side of the
coin, once the UT OFFSET has been set ASTROCLK's local
coordinates may be set as desired and the current correct local
time will be calculated and displayed and UT TIME will remain
constant. ASTROCLK will adjust ALL local times by one hour if the
DAYLIGHT FLAG is set; given that the dates when daylight time is
in effect vary considerably around the world, users may find it
more convenient to leave the DAYLIGHT FLAG off when away from
their "home" time zone(s), turning it on only when certain of the
local standard. See also the discussion of the UT TIME ZONE
OFFSET in the NAVIGATION section.
When used in the static mode, the clocks are stopped. The
user may enter any desired location or time/date and all
calculations will be made using that data. Note that West
longitudes and South latitudes must be entered as negative
numbers for ASTROCLK. (CAUTION: Some texts and institutions do
not observe the same sign conventions!) The basic calculations in
ASTROCLK are based upon formulae accurate for Epoch J2000.0.
Negative dates, that is dates "B.C.", display in RED (BLINK in
all monochrome modes) and there is no year 0000; the sequence of
years near zero is -2, -1, 1, 2, etc. The accuracy of some of the
celestial data will decrease as the time difference from Epoch
J2000.0 increases.
Although UTC and UT (=UT1) are not the same, they are
maintained to within 0.9 seconds of each other by the occasional
insertion of Leap Seconds at the end of June or December. In 1988
the difference is typically less than 0.2 seconds. While software
programs are available to precisely set a computer's clock using
telephone signals from NBS, this accuracy cannot usually be
maintained for extended periods of time. In any event, frequent
calls to NBS are impractical for most of us by reason of cost. A
more cost effective solution is to use the Heath/Zenith GC-1000
Most Accurate Clock and its optional software to synchronize the
computer's clock. The GC-1000 is a combination receiver and clock
and when equipped with an RS-232 interface and external antenna,
it can maintain UTC time to within 10 milliseconds.
I have therefore elected to treat UTC as equal to UT for
time and date displays and have actually assumed UT time and date
in all but one case: the correct UTC time relative to UT is
calculated and displayed on Precision Time Display #1 but it is
otherwise not used. All other times and dates are referenced to
UT rather than to UTC. This minor technical error represents a
compromise between technical accuracy and ease of use.
While the times displayed by ASTROCLK in the various small
windows are rounded to the nearest second, any time (Local, UT,
or TDT) may be entered using Function Key F3 to a precision of
approximately 0.0001 seconds and will be used to that precision
in the various calculations. Compare the times shown in the small
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 36
windows with those in the Precision Time Display #1. Except for
some items in the Precision Time Displays, this additional
precision is usually not significant. See the section PRECISION
AND ACCURACY TESTS for additional comments.
Setting the LOCAL/UT/TDT Time
The time entry format is very flexible and for convenience
will accept either the traditional colon (":") or the comma (",")
as the separator between hours and minutes or minutes and
seconds; the examples are shown with the colon only. Each item
(hours, minutes, or seconds) can accept a decimal fraction
although normally only the last item entered would have a
fractional part. Time entries are ALWAYS made using the 24-hour
convention. The following are all acceptable time entries:
HH Hours
HH.HHHHHH Hours + fractional hours
HH:MM Hours:Minutes
HH:MM.MMMM Hours:Minutes + frac mins
HH:MM:SS Hours:Minutes:Seconds
HH:MM:SS.SS Hours:Minutes:Seconds + frac
The "standard" date input format requires the day, month,
and year (in that order, European style, and separated by commas)
in either of the following two formats:
DD,MM,YYYY
DD.DDD,MM,YYYY
The first format specifies the date to be used with the existing
or just input time; unless the letter "U" or "T" has been
appended to the time input (see below), the date is the LOCAL
date. The second format, containing a fractional day (including
"." alone or ".0") specifies a UT date with the time implicit to
allow the astronomical convention where dates are often given in
the form "1988 JAN 1.5"; this would be entered as "1.5,1,1988".
The time input is ignored with this format (press RETURN). The
fractional part may have as many digits as desired, but more than
about six digits usually are not significant.
It is sometimes convenient to set the time and date using
UT (=UT1) data. This avoids having to make the conversions
mentally. If you add the letter "U" at the end of the time or
date entry, ASTROCLK will perform the appropriate time or date
conversions automatically, based upon the current settings of the
DAYLIGHT FLAG and ZONE CORRECTION. If you add "U" to your time
input to enter UT time, ASTROCLK assumes that you are also
entering UT date. If you enter a fractional part of a day as part
of the date input, the time input is ignored and UT date is
assumed (see the preceeding paragraph).
As an example, to set the time and date to 9:44:30 UT on
November 13, 1978, use the following entries:
9:44:30U (UT time)
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 37
13,11,1978 (UT date)
Alternatively, the same time and date may be input by pressing
RETURN for the time, and using the following date entry (with the
fractional part of the day representing the desired time):
13.405903,11,1978 (UT date, time implicit)
If Terrestrial Dynamical Time (or Ephemeris Time prior to
1984) is desired, add the letter "T" (or "E") at the end of the
time entry. ASTROCLK automatically selects TDT or ET based upon
the date regardless of the letter used to designate the time
during input. Note that the displayed UTC DATE may not correspond
to that input if the time is within the period Delta T (TDT-UT)
of midnight. ASTROCLK automatically adjusts the date to agree
with the information input and near midnight this can be
confusing to the user!
Setting the LOCAL/UT Date
The date input routine will also permit the entry of the
Julian Date (JD), Dublin Julian Date (DJD), Modified Julian Date
(MJD), Truncated Julian Date (TJD), or Greenwich Sidereal Date
(GSD) by prefixing the date with the appropriate two or three
letters followed by the desired date. Whenever letters are used,
they may be input in upper or lower case. Note that when an
integer GSD is entered (no fraction to the right of the decimal
point), the resulting UT time is the Greenwich Transit of the
Mean Equinox at 0h GMST for that date. The following formats are
available:
JDddddddd.dddddd Julian Date
DJDddddddd.dddddd Dublin Julian Date
MJDddddddd.dddddd Modified Julian Date
TJDddddddd.dddddd Truncated Julian Date
GSDddddddd.dddddd Greenwich Sidereal Date
Decimal fractions of a day may also be included, as shown
above and in the subsequent examples, but more than six digits to
the right of the decimal point will probably not be significant
in most calculations. If the current date plus or minus a number
of days is desired, the form +nnn or -nnn may be used with "nnn"
being the desired number of days. Entering "#" alone will yield
the current Julian Date at 00:00:00 UT; entering "*" alone will
yield the exact current Julian Date (useful for precession
calculations with Function Key F8). Examples:
+3 Current JD + 3 days
-10 Current JD - 10 days
+1.5 Current JD + 1.5 days
# Current JD @ 00:00:00 UT
* Current JD
Similarly, dates may be input as Julian or Besselian Epochs
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 38
by prefixing the epoch with the letter "J" or "B" respectively.
Two formats are available:
Jyyyy.yyyyyy Julian Epoch
Byyyy.yyyyyy Besselian Epoch
Finally, inspired by the desire to interpret dates on images
during Voyager 2's close encounter with Neptune in August 1989,
dates may be input as the current Day-of-the-Year, with January 1
being Day 1. Note that this method may ONLY be used for the
year currently set and displayed. UT Hours, minutes and seconds
may be included if desired, as shown by the following format
examples:
Dnnn[.nnnn] Day Number
Dnnn:hh[.hhhh] Day + UT Hours
Dnnn:hh:mm[.mm] Day + UT Hours+Minutes
Dnnn:hh:mm:ss[.ss] Day + UT Hrs+Mins+Secs
When these special forms of date input are used, you may
press RETURN in response to the time prompt since UT time is
implicit in the date format; any time that is input will be
overridden and the implicit time associated with the date used
instead. All of these date formats are calculated in Display Mode
7, Julian Date Information, and that display may be used to
easily convert dates from one format to another; while in Display
Mode 7, use F3 to enter the date in one format and read the
desired conversion on the screen. For example, the following date
entries are equivalent to July 2, 1988 at 03:00:00 UT to within a
few seconds:
JD2447344.625
DJD32324.625
MJD47344.125
TJD7344.125
GSD2454045.903811
J1988.5
B1988.501032
NOTE: If you enter a date as a simple number, greater than
50 and without a letter or sign prefix such as "JD" or "+",
ASTROCLK assumes that you wish to enter the Julian Date and
simply neglected to include the "JD" prefix. The program
therefore interprets such entries (up to the first comma, if
present) as Julian Dates and no warning or error message is
generated. (ASTROCLK versions prior to 8831 would sometimes
generate a QuickBASIC error and abort ASTROCLK in this situation
because the number was interpreted as the day of the month.)
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 39
SETTING LOCAL AND DESTINATION COORDINATES
Before most of the data displayed by ASTROCLK can be of any
practical use, you must set your own geographical coordinates
into the program using Function Key F6. On startup, ASTROCLK uses
the coordinates for Rancho Palos Verdes, California, near Los
Angeles. If you do not know your coordinates, I recommend that
you consult Goode's World Atlas, 17th Edition, which includes an
extensive Index with longitudes and latitudes of some 30,000
cities and other locations worldwide. All coordinates are given
to one minute of arc, and this is the only atlas I know which
includes this information. NOTE: In spite of the format used for
the coordinates in Goode's, 118.34 for example, the portion to
the right of the decimal point represents minutes NOT decimal
parts of a degree. See the BIBLIOGRAPHY for the full reference.
With the addition of navigation functions to ASTROCLK,
Function Key SHIFT-F6 has been included to allow destination data
to also be read from the same "city file". The operation of
SHIFT-F6 is identical to normal operation of Function Key F6
decribed below except that the DESTINATION name and geographic
coordinates are set rather than the LOCAL name and coordinates.
The destination data are disabled when ASTROCLK is first started.
See the section CELESTIAL NAVIGATION for additional discussion.
The following prompt will appear in the main window after
pressing F6:
SET LOCAL COORDINATES
Enter CITY NAME to search for in file
\ASTROCLK\ASTROCLK.CTY
Enter desired name: _
Match starts at left of name. Prefix input
with '/' to match input anywhere within
the name. Matches are case insensitive.
Press RETURN for MANUAL data entry.
When using SHIFT-F6, the display is the same except that the
title includes the word DESTINATION instead of LOCAL and you may
also enter the name as "*" to set the DESTINATION coordinates to
the current LOCAL coordinates. The file name shown in the example
is the standard city file supplied with ASTROCLK.
Using file ASTROCLK.CTY, you may automatically enter the
data for any of the cities included in that file. Other "city
files" may be available or may be created as required. Enter the
name or first part of the name of the desired city. Only letters
sufficient to unambiguously select the city are required, either
upper or lower case may be used, and spaces are significant. For
example, "k" is sufficient for "Kansas City" since there is
currently only one city beginning with the letter K, but "san f"
is required to distinguish "San Francisco" from "San Antonio",
"San Diego", etc. The search stops at the first match, so "san"
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 40
would first match "San Antonio" and you would have to press the
space bar several times before you reached "San Francisco".
Alternatively, you may prefix the name you enter with the
"/" character (without the quotation marks) and ASTROCLK will
attempt to match your input anywhere within the file's city
names. For example, a special navigation city file of VOR's,
USWEST.VOR, includes the three letter code designation for each
VOR in addition to the full name; the code for the Los Angeles
VOR is "LAX". To select Los Angeles by the code designation, you
may enter "/lax" (again without the quotation marks and in either
upper or lower case). Using this method with too short or simple
a designation may find many qualifying matches.
For each qualifying match found, ASTROCLK presents the data
read from the file and awaits your choice: press RETURN to ACCEPT
the data shown, or press the SPACE BAR to look for the next
match. If in doubt, consult the list below or print the file
ASTROCLK.CTY to obtain the current list of cities. ASTROCLK.CTY
is an ASCII file and may be edited to modify the data; use non-
document mode and observe the comma-delimited format when making
additions or changes.
Three geographical locations are "hard coded" (for my own
personal convenience) and may be selected by entering the
following abbreviations for the local name (upper or lower case):
RPV Rancho Palos Verdes, CA
CAL Calaveras County, CA
USNO U. S. Naval Observatory, Washington, DC
To manually enter local coordinates (instead of searching
the external file), press RETURN when asked for the city name.
Then enter LONGITUDE, LATITUDE, ELEVATION, and NAME when
requested. WEST longitude and SOUTH latitude must be entered as
NEGATIVE numbers. Press RETURN to skip an entry and leave it
unchanged except ELEVATION which is reset to zero.
A special program, MAPCOORD, is available from my bulletin
board system which may be used to generate city files or to
append new entries to an existing city file. Other city files,
including file USWEST.VOR mentioned above, are also available.
The listing of file ASTROCLK.CTY which follows gives the
approximate longitude and latitude for selected cities in the
United States and Canada. All coordinates are given in degrees to
two decimal places and have been estimated to an accuracy of
about 0.5 degrees or better. NOTE: West longitudes are shown as,
and must be entered as, as negative numbers.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 41
Listing of File ASTROCLK.CTY
CITY LONGITUDE LATITUDE
--------------------------------------------------
Albuquerque, NM -106.50 35.00
Atlanta, GA -84.25 33.75
Baltimore, MD -76.62 39.25
Birmingham, AL -85.83 33.50
Boston, MA -71.08 42.17
Buffalo, NY -78.83 42.92
Chicago, IL -87.67 41.83
Cleveland, OH -81.67 41.50
Columbus, OH -83.00 39.95
Dallas, TX -97.83 32.83
Denver, CO -105.00 39.75
Detroit, MI -83.00 42.33
El Paso, TX -106.42 31.78
Ft. Lauderdale, FL -80.08 26.17
Ft. Worth, TX -97.33 32.75
Greensboro, NC -79.75 36.08
Hartford, CT -72.67 41.75
Honolulu, HI -157.83 21.33
Houston, TX -95.33 29.75
Indianapolis, IA -86.17 39.75
Kansas City, KS/MO -94.58 39.12
Las Vegas, NV -115.17 36.17
Los Angeles, CA -118.25 34.00
Louisville, KY -85.75 35.25
Memphis, TN -90.08 35.17
Miami, FL -80.17 25.75
Milwaukee, WI -88.00 43.00
Minneapolis, MN -93.25 45.00
New Orleans, LA -90.08 30.00
New York, NY -73.50 40.50
Newark, NJ -74.17 40.70
Norfolk, VA -76.33 36.83
Oakland, CA -122.25 37.75
Oklahoma City, OK -97.50 35.00
Philadelphia, PA -76.17 39.92
Phoenix, AZ -112.08 33.42
Pittsburg, PA -80.00 40.42
Portland, OR -122.50 45.50
Providence, RI -76.42 41.92
Rochester, NY -77.58 43.17
Richmond, VA -77.42 37.58
Riverside, CA -117.33 34.00
St. Louis, MO -90.17 38.62
Sacramento, CA -121.50 38.58
Salt Lake City, UT -112.00 40.75
San Antonio, TX -98.50 29.42
San Diego, CA -117.17 32.75
San Francisco, CA -122.42 37.75
San Jose, CA -121.92 37.33
San Pedro, CA -118.31 33.74
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 42
CITY LONGITUDE LATITUDE
--------------------------------------------------
Santa Monica, CA -118.50 34.00
Seattle, WA -122.33 47.67
Springfield, MA -72.58 42.08
Toledo, OH -83.50 41.67
Trenton, NJ -74.75 40.25
Washington, DC (USNO) -77.07 38.92
Wilmington, DE -75.50 39.75
Calgary, Alberta -114.00 51.00
Edmonton, Alberta -113.50 53.67
Halifax, Nova Scotia -63.58 44.67
Hamilton, Ontario -79.50 43.25
Montreal, Quebec -73.58 45.50
Ottawa, Ontario -75.67 45.42
Quebec, Quebec -71.17 46.87
Regina, Saskatchewan -104.50 50.50
Toronto, Ontario -79.33 43.67
Vancouver, British Columbia -123.08 49.25
Winnipeg, Manitoba -97.25 49.92
An additional city file, USCITIES.CTY, is also available and
includes some 718 U. S. cities with greater accuracy than that
shown above. No Canadian cities are included in USCITIES.CTY.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 43
SETTING LOCAL CONDITIONS
ASTROCLK makes certain default assumptions about the current
conditions when computing horizon dip (a function of the
observer's elevation above mean sea level) and atmospheric
refraction. These calculations are used in the Horizon (Observer)
Coordinates data in Display Mode 0 and for certain navigation
calculations. The default values are:
Elevation: 0 meters/feet
Temperature: 20 degrees Centigrade
68 degrees Farenheit
Pressure: 1010 millibars
29.83 inches of Mercury
If these default values are not representative of your
current conditions, use ALT-F6 to set the correct LOCAL
CONDITIONS. The following information will be displayed:
SET LOCAL CONDITIONS
Current ELEVATION: 152.4 m = 500.0 ft
Current TEMPERATURE: 20.0 C = 68.0 F
Current PRESSURE: 1010 mb = 29.83"
The following prompts will be displayed to enable you to change
each item:
Enter ELEVATION (meters):
Enter TEMPERATURE ( C):
Enter PRESSURE (mb):
For each item, press RETURN to leave that item unchanged or enter
the new information. Elevation assumes the entry in meters unless
you add the letter "F" to specify FEET, Pressure assumes degrees
Centigrage unless you add the letter "F" to specify degrees
Farenheit, and Pressure assumes millibars unless you enter a
number less than 32.00 or add the letters "IN". Note that in the
United States and for air traffic control, pressures are often
given in hundreths of an inch, as in "2983"; this must be entered
as "29.83".
When all three items have been entered or accepted as is,
the following prompt will appear:
Press RETURN to ACCEPT, SPACE to REDO:
Press RETURN to accept the entries as shown, or press SPACE BAR
to start over.
Since the elevation of a geographic location will probably
remain constant with time, absent some major disturbance, that
value is saved in the file ASTROCLK.INI and is restored each time
ASTROCLK is restarted. However, the values for temperature and
pressure, being quite variable, are not saved and are restored to
their default values each time ASTROCLK is restarted.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 44
DUAL-TIME DISPLAYS
A Dual-Time display feature is available which displays two
different, selectable times in large characters in the main
display window. Display Modes 1 through 5 normally display the
following times in large characters in the main screen window:
1 Local Standard/Daylight Time
2 Universal Coordinated Time
3 Local Mean Sidereal Time
4 Greenwich Mean Sidereal Time
5 Terrestrial Dynamical Time
(Ephemeris Time prior to 1984)
Display Mode 1, Local Standard/Daylight Time, is the display
mode which appears when program ASTROCLK is started. The large
digit time display modes may be selected at any time by pressing
the number keys 1 through 5. Use the number keys at the top of
the keyboard and NOT the number keys on the numeric keypad. The
title at the top of the main window gives the standard
abbreviation and full name of the time displayed.
To enable a dual-time display, select one of the clock
display modes using the number keys 1 through 5, and then press
the UP or DOWN arrow key. The normally displayed time will move
up in the window and a second time will appear in yellow in the
lower half of the window. Repeated pressing of the UP or DOWN
arrow key will cycle through the following lower clock displays:
PST/PDT Pacific Standard/Daylight Time
MST/MDT Mountain Standard/Daylight Time
CST/CDT Central Standard/Daylight Time
EST/EDT Eastern Standard/Daylight Time
TAI/A.1 International Atomic Time (after 1971)
USNO Atomic Time (1958 through 1971)
5 TDT/ET Terrestrial Dynamical Time (after 1983)
Ephemeris Time (prior to 1984)
4 GMST Greenwich Mean Sidereal Time
3 LMST Local Mean Sidereal Time
2 UTC Universal Coordinated Time
1 LST Local STANDARD/DAYLIGHT Time (Mode 1 only)
Local STANDARD Time (Modes 2 thru 5)
The UP arrow key cycles UP through the list above starting
with the normal time for that display mode as indicated by the
numbers at the left; the DOWN arrow key cycles DOWN through the
list. Each display may be returned to the normal, single-time
mode by pressing the HOME key. Note that the first five times
listed can ONLY be displayed in large digits by using the DUAL
TIME method.
The first four times are for the standard time zones in the
continental United States and will display Standard or Daylight
time in agreement with the current setting of the Daylight Flag
(ALT-F10). If the local time is a continental U. S. time zone, it
is possible to display the same time in both the upper and lower
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 45
portion of the window in Display Mode 1. These times are
calculated independently of the current local time zone.
When the dual-time display is enabled, the abbreviation
corresponding to the time displayed will also appear at the right
of the time digits for each clock. For time zones in the United
States, the abbreviation will change from LST (Local Standard Time)
to the common U. S. abbreviation: PST for Pacific Standard Time,
EST for Eastern Standard Time, HST for Hawaiian Standard Time,
etc. The single or dual time selected for each of the five
display modes is saved while ASTROCLK is running; changing to a
different Display Mode and back again will display the same
time(s). The single or dual time selected for each mode is also
saved in file ASTROCLK.INI and will be restored when ASTROCLK is
run the next time.
Note that the Local STANDARD Time can be selected for the
lower clock in Display Modes 2 through 5, whether or not the
DAYLIGHT FLAG has been set. During daylight time, therefore, this
display will show a different time from the small LOCAL TIME
display on the right of the screen. Since some references and
magazines give all times in standard time, this display will
eliminate having to make the conversion if you are on daylight
time.
If the date has been set for 1958 through 1971, U.S. Naval
Observatory Atomic Time (USNO A.1) is displayed instead of
International Atomic Time (TAI). If the date has been set prior
to 1958, a message in the lower portion of the window will remind
the user that TAI and A.1 did not exist on the selected date.
There is a slight (0.034 seconds) difference in the relationship
of the two atomic time scales to TDT/ET.
If the date has been set prior to 1984, Ephemeris Time (ET)
is displayed instead of Terrestrial Dynamical Time (TDT). For
most purposes, TDT and ET represent a continuous time scale and
are treated as such by ASTROCLK; the only difference is the name
displayed.
There are, of course, many combinations possible. For
example, you can display UTC and Local STANDARD Time, UTC and
GMST, GMST and LMST, TDT and TAI, and so forth. If you are about
to call the East from Los Angeles, you can display both Eastern
and Pacific times, Standard or Daylight depending on the current
setting of the Daylight Flag. Each of the five display modes is
independent of the other four, and may be set up to display
either its normal time alone, or dual time with one of the other
remaining times.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 46
ALARM AND INTERVAL TIMER OPERATIONS
ASTROCLK includes alarm and interval timer functions which
operate independently of the program's clock modes. That is, the
alarm and interval timer ALWAYS use the computer's internal clock
for their operations, even with the ASTROCLK clocks off or in the
simulation mode. The correct alarm and interval times, referenced
to the computer's internal clock (Local Time), are therefore
displayed in all clock modes. The interval timer window is
displayed at all times at the lower center of the screen, but the
alarm window is only displayed at the lower right of the screen
when an alarm is active.
Using the ALARM Function
The alarm function allows the user to set an alarm to any
time within the next 23 hours using either Local or UT Time. When
an alarm is active, the program opens a small Alarm Window at the
lower right corner of the display screen which displays the
selected alarm time in the left side of the window and the
coundown time, or time remaining until the alarm, in the right
side of the window. The color of the countdown time changes as
the local time approaches the selected time, from gray to white
to yellow to blinking yellow.
To set or change the alarm time, press Function Key SHIFT-F3
and enter the desired Local or UT Time in the format HH:MM:SS,
HH:MM or HH.HHH, using the same flexible format rules as for
setting the program time. If you prefer, use the comma instead of
the colon for the separator between units. Add the letter "U" if
the alarm time you are entering is UT Time; ASTROCLK will
automatically convert the UT Time to Local Time and the Local
Time will be displayed in the Alarm Window. If an alarm time has
already been set and you wish to clear it, press SHIFT-F3 and
then simply press RETURN instead of entering a time.
Once an alarm time has been set using Function Key SHIFT-F3,
the alarm countdown time (the time remaining until the selected
alarm time is reached) may also be displayed in the main display
window by pressing the letter "A" on the keyboard. The small
window at the lower right of the display screen will still show
both the selected alarm time and the countdown time. If no alarm
time has been set, pressing the letter "A" will have no effect.
The alarm function remembers the prior main window display
function; if the alarm countdown time is displayed in the main
display window when the alarm time is reached, the main display
will automatically revert to the prior function. As further
described below, the interval timer can also be synchronized to
the time an alarm occurs.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 47
Using the INTERVAL TIMER
ASTROCLK includes an interval timer function, measuring
elapsed time rounded to the nearest second. The current value of
the interval timer is always shown in the TIMER window at the
lower center of the display in the format 00 00:00:00,
corresponding to days and hours:minutes:seconds. The TIMER window
allows times from +9999 days to -999 days; the days portion will
be blanked if the day count falls outside this range. When the
Interval Timer is displayed in the main display window using the
"T" command, the range for that display is from +999 days to -99
days; the main window display should not be used outside this
range as the interval time will NOT be updated. The interval
timer display in the TIMER window is white (gray) when the timer
is OFF, and yellow when the timer is ON.
The following keys are used to control the operation of the
interval timer:
T Display interval timer in main display window
S Start/Stop the interval timer without reset
Z Stop and reset the interval timer
PgUp Increment the interval timer DAYS
PgDn Decrement the interval timer DAYS
NOTE: The PgUp and PgDn keys are only active when the
interval timer is displayed in the main display window
using the "T" command.
The interval timer may be started by one of three methods:
manually, by pressing the letter "S"; automatically, when an
alarm time occurs AND the interval timer is not already ON; or by
setting the interval timer starting time with Function Key SHIFT-
F3. When the interval timer is started automatically or by
setting its starting time, it starts at zero. Note that the
interval timer will NOT be automatically reset and started by the
alarm function if it is already ON; in this case the interval
timer will be unaffected by alarm operations.
The interval timer starting time may be set using Function
Key SHIFT-F3. Enter the desired starting time followed by the
letter "T". If the entered time is later than the current time,
ASTROCLK assumes the prior day. The total elapsed time will
therefore always be less than 24 hours. To adjust the starting
DAY, set the desired starting time, display the interval timer in
the main display window using the "T" command, then use the PgUp
and PgDn keys to set the days.
Press the letter "S" to start or stop (but not reset) the
interval timer. The timer may be stopped and started as often as
desired whether or not the interval timer is displayed in the
main display window. Press the letter "Z" to stop the interval
timer and reset the accumulated time to zero. When the interval
timer is displayed in the main display window and the timer is
stopped, the words "TIMER IS HOLDING" will flash at the bottom of
the window.
The status of the interval timer is saved when ASTROCLK is
halted. If the interval timer is active when the program is
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 48
halted, it will resume operation when next the program is started
and the correct elapsed time interval (including days) will be
displayed. If the interval timer is stopped but not reset when
ASTROCLK is halted, the current elapsed time will be restored and
the interval timer will be stopped when next the program is
started.
Linked ALARM & INTERVAL TIMER Operation
If the interval timer is stopped and reset when the alarm
time occurs, the interval timer will auotmatically start at the
alarm time. The alarm and the interval timer then function
together as a count-down-then-count-up timer. A typical operation
in this manner may best be illustrated by an example. I used this
arrangement during the launch of the Space Shuttle DISCOVERY on
September 29, 1988 and throughout the four day mission. I first
checked the system clock using radio station WWV from the
National Bureau of Standards.
To set up ASTROCLK correctly, I pressed "Z" to stop and
reset the interval timer (if it did not display 00 00:00:00),
next entered the scheduled lift-off time on the alarm using
Function Key SHIFT-F3, then pressed the letter "T" to display the
interval timer (to establish the "prior display mode" for the
alarm function), followed by the letter "A" to display the alarm
countdown time. ASTROCLK displayed the countdown time until lift-
off and then automatically switched the main display to the
interval timer to show Mission Elapsed Time (MET) throughout the
four day mission. The main display may be switched to other
display functions without affecting the accuracy of the countdown
or elapsed times. Once the interval timer has started, ASTROCLK
may be halted and restarted and the time will be preserved. Since
the interval timer can continue for up to 9999 days, any mission
or other event of reasonable duration can easily be handled.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 49
TARGET TRACKING DISPLAY
One of the problems that inspired program ASTROCLK in the
first place was my inability to figure out where a star or planet
could be located in the night sky even if I knew its equatorial
coordinates, the right ascension and declination. These
coordinates have to be converted to horizon coordinates, also
known as observer coordinates, in order to relate the position of
a star with my own position and the time. (Of course, I had to
know the direction of true North as well, but even I could
usually find Polaris without excessive difficulty.)
Display Mode 0, the Target Tracking Display, provides this
information in real time for both stars and planets -- although
there are significant computational delays associated with the
planetary positions if the micro-computer does not have a math
coprocessor. The default target is Polaris, the North Star, which
I have assigned the number zero in ASTROCLK's internal star
database. Use Function Key F5 to select other celestial objects
for tracking. Pressing "P" while in the Target Tracking Display
will request the planet to track and then automatically calculate
and display the position data for the planet.
When already in Display Mode 0, the Target Tracking Display,
pressing the "0" key again toggles between the full display (as
described in the following paragraphs) and a large digit display
showing the Horizon Coordinates for the target, with the APPARENT
ALTITUDE on the top line and the AZIMUTH on the bottom line. The
format will change with Function Key F7 (see below). However, the
precision of the large digit display is two digits fewer than the
full (text) display due to restricted display space.
The following sample display shows the information available
in the Target Tracking Display. The degree symbol, which appears
in the actual display, has been deleted from the sample because
of the differences among printers.
0 - a Ursae Minoris - Polaris
-----------------------------
EQUATORIAL COORDINATES [J2000.0]:
RIGHT ASCENSION: 2:31:48.70
DECLINATION: 89 15'50.72"
HOUR ANGLE (hours): 17:07:49.20
APPARENT COORDINATES [J1988.9]:
RIGHT ASCENSION: 2:20:08.44
DECLINATION: 89 12'51.34"
HOUR ANGLE (hours): 17:19:29.45
OBSERVER HORIZON COORDINATES:
ALTITUDE: 33 37'33.09"
AZIMUTH (NESW): 0 55'44.18"
Apparent ALTITUDE: 33 38'57.11"
[Charts SA=1 U=I-1] [VMag = 2.02]
The Equatorial Coordinates are first shown for the current
epoch of the internal star database; the default is J2000.0, as
shown in the sample above. These data are "mean" positions for
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 50
the epoch shown, as found in typical star catalogs.
The Apparent Coordinates are the apparent geocentric
equatorial coordinates which have been (for stars) precessed and
corrected for proper motion, nutation, and annual aberration but
NOT parallax, or (for planets) calculated as of the mean equinox
of date, J1988.9 in the sample. The stellar apparent geocentric
equatorial coordinates agree with the Astronomical Almanac and
the USNO Interactive Computer Ephemeris to an accuracy of
typically less than one second of time or arc; planetary data are
less accurate.
Versions of ASTROCLK prior to 8847 displayed "apparent
coordinates" which were the current star database coordinates
adjusted for refraction. The present display is in keeping with
the accepted definition of "apparent" (that is, referenced to the
mean equinox of date), and the coordinates have NOT been
corrected for refraction.
The local HA (Hour Angle, hours) is related to the RA (Right
Ascension, hours) and LMST (Local Mean Sidereal Time, hours) by
the formula:
HA = LMST - RA
Technically, the LAST Local Apparent Sidereal Time should be
used, but I have compromised, as have some of my sources, since
the difference is small (on the order of 0.2 seconds in 1988) and
many calculations can thereby be avoided; while not particularly
important if your computer has a math coprocessor, the delay may
be significant if it does not.
The Horizon (or Observer) Coordinates are referenced to the
current ASTROCLK local geographical coordinates. The Altitude is
the angle above the true horizon, and the Azimuth is the angle
from true North, measured in the sense NESW. Thus, North is 0
degrees, East is 90 degrees, South is 180 degrees, and West is
270 degrees. The Apparent Altitude is the Altitude corrected for
atmospheric refraction and horizon dip (if the local elevation is
non-zero); Azimuth is unaffected by refraction.
The approximate visual or photographic magnitude of the
object is shown at the lower right of the window border, marked
as "VMAG" (visual magnitude) for stars and planets or "BMAG"
(blue/photographic magnitude) for minor planets. The values for
stars are constant values from the internal or external catalog
while those for planets and minor planets are calculated
approximations for the current time and date.
The chart numbers in two of the most commonly used star
atlases are shown for the target object in the Chart data at the
lower left of the target window. "SA=" gives the chart number in
Sky Atlas 2000.0 and "U=" gives the volume(s) and chart number
for Uranometria 2000.0. Of course, the target object may or may
not appear on the chart, depending upon the type of object and
its magnitude; planets, for example, will not appear because of
their constantly changing positions. Even when the object does
not appear on the chart, however, the chart for the proper area
may be useful to establish neighboring stars, the constellation
name, etc. The original algorithm used to calculate the chart
numbers was published in Sky & Telescope Magazine in April 1989;
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 51
the algorithm has been substantially modified and converted to
QuickBASIC for use in ASTROCLK.
Function Key ALT-F7 changes some of the units used for the
Target Tracking Display, as shown in the following sample (and
again, the degree symbol has been deleted).
0 - a Ursae Minoris - Polaris
-----------------------------
EQUATORIAL COORDINATES [J2000.0]:
SIDEREAL HR ANGLE [SHA]: 322 02'49.43"
DECLINATION [DEC]: 89 15'50.72"
GREENWICH HR ANGLE [GHA]: 15 21'29.95"
APPARENT COORDINATES [J1988.9]:
SIDEREAL HR ANGLE [SHA]: 324 57'53.18"
DECLINATION [DEC]: 89 12'51.34"
GREENWICH HR ANGLE [GHA]: 18 16'33.70"
OBSERVER HORIZON COORDINATES:
ALTITUDE [Hc]: 33 37'33.09"
AZIMUTH (NESW) [Zn]: 0 55'44.18"
Apparent ALTITUDE [Ho]: 33 38'57.11"
[Chart SA=1 U=I-1] [VMag = 2.02]
This alternate form of the Target Tracking Display shows the
same basic information as above, but in a form preferred by
navigators. Press ALT-F7 again to return to the original format.
SHA (Sidereal Hour Angle, degrees) is related to RA (Right
Ascension, hours) by the formula:
SHA = 360 - RA * 15
GHA (Greenwich Hour Angle, degrees) is related to SHA (Sidereal
Hour Angle, degrees) and GAST (Greenwich Apparent Sidereal Time,
hours) by the formula:
GHA = 15 * GAST + SHA
Not shown but also occasionally required is LHA (Local Hour
Angle, degrees) which is obtained using the following formula:
LHA = GHA + Longitude
The abbreviations shown in square brackets [...] are those given
in the Nautical Almanac and the USNO Almanac for Computers for
use in navigation.
Note that in this mode, the Apparent Altitude will show the
abbreviation [Ho] if the local elevation is zero, and [Hs] if the
local elevation is non-zero. [Ho] refers to the "observed"
altitude after corrections for horizon dip and instrument error,
while [Hs] refers to the "sextant" altitude after correction for
instrument error but as measured to the actual horizon. If the
navigational instrument being used provides its own artificial
horizon, set the local elevation to zero.
Function Key F7 may be used to change the units used in the
Target Tracking Display. Three different formats for time and
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 52
degrees are available; press F7 to cycle through the formats:
ANGLES TIME
------------ -----------
DDD MM SS.SS HH:MM:SS.SS
DDD MM.MMMM HH:MM.MMMM
DDD.DDDDDD HH.HHHHHH
However, note that the large digit display (showing Apparent
Altitude and Azimuth) and obtained by pressing the "0" key when
in the Tracking Data Mode, displays the data to lower precision
due to screen space restrictions.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 53
TARGET OBJECT EPHEMERIS
Quite a number of ASTROCLK users have requested the
capability of displaying and/or printing an ephemeris, a listing
of the position of a celestial object for a series of specific
dates and times. While ASTROCLK was intended more as a real time
clock and tracking program than for the generation of tabular
data, it is admittedly very useful to be able to produce such a
listing in anticipation of an evening with behind your telescope.
Because of increasingly severe memory constraints, direct
printing is not possible with this version of ASTROCLK except by
using the SHIFT-PrtSc key. However, Function Key F2 now displays
an ephemeris for the current target object, replacing the
previous function of cycling through the various clock displays.
Before pressing Function Key F2, ASTROCLK must be set up for
the desired target object (star, planet, minor planet, etc.)
using Function Key F5. For most objects outside the solar system,
of course, the position will change very slowly with time. Next
set the desired starting time using Function Key F3. Two
additional items are required before the ephemeris can be
displayed, the step interval (the time from one calculation to
the next) and the number of intervals.
SET TARGET EPHEMERIS PARAMETERS
The ephemeris will be generated for the current
TIME and DATE. Use F3 to change.
Enter INTERVAL [1 day]:
Enter the ephemeris step interval in DAYS, or:
Add 'Y' or 'y' for 365-day YEARS.
Add 'H' or 'h' for HOURS.
Add 'M' or 'm' for MINUTES.
The default units for the interval are DAYS; simply enter
the number of days between steps and press RETURN. If you wish
other units, 365-day years, hours, or minutes, add the letter Y,
H, or M (upper or lower case) respectively following the number.
Enter number of intervals [10]:
Then enter the total number of intervals desired or press RETURN
for 10 intervals. ASTROCLK will generate the ephemeris with 20
lines per display screen. When the complete ephemeris has been
displayed and each time the screen fills, the program will pause
so that you may read or print the information. Press any key to
continue. After the ephemeris is completed, ASTROCLK will resume
normal operation.
The following is a sample ephemeris generated for the planet
Neptune on August 30, 1989 with an interval set to one day and
ten intervals requested:
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 54
ASTROCLK EPHEMERIS FOR: Planet #8 NEPTUNE (Automatic)
Equinox of Date [J1989.6]
Julian Date Local Date PDT Time Rt. Ascen. Declination
2447769.478183 30-08-1989 16:28:35 18:42:04.82 -22 10'38.63"
2447770.478183 31-08-1989 16:28:35 18:42:02.00 -22 10'43.65"
2447771.478183 01-09-1989 16:28:35 18:41:59.31 -22 10'48.61"
2447772.478183 02-09-1989 16:28:35 18:41:56.75 -22 10'53.43"
2447773.478183 03-09-1989 16:28:35 18:41:54.31 -22 10'58.11"
2447774.478183 04-09-1989 16:28:35 18:41:52.00 -22 11'02.67"
2447775.478183 05-09-1989 16:28:35 18:41:49.83 -22 11'07.07"
2447776.478183 06-09-1989 16:28:35 18:41:47.79 -22 11'11.35"
2447777.478183 07-09-1989 16:28:35 18:41:45.90 -22 11'15.52"
2447778.478183 08-09-1989 16:28:35 18:41:44.13 -22 11'19.54"
As usual in these text examples, the degree symbol has been
omitted because of printer differences, and the right-most
column, giving the object's magnitude, has been deleted because
of space limitations; the value was 7.89 and 7.90 for the dates
shown. The Local Date and Time are based upon the current
geographical coordinates and time corrections (DAYLIGHT FLAG and
ZONE CORRECTION); the time zone abbreviation, PDT in the example,
is also included. Note that the coordinates shown are the
Apparent Geocentric Equatorial Coordinates for the Epoch and
Equinox of Date, J1989.6 in the example.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 55
PRECISION TIME AND DATA DISPLAYS
The ASTROCLK on-screen clocks on the right portion of the
screen display times rounded the nearest second. It is sometimes
useful to view the various times and other parameters to a higher
precision. Display Mode 8 provides this facility with five
precision displays: two Precision Time Displays and three
Precision Data Displays. Switch between the displays with the
PgUp or PgDn keys, or press the "8" key. When ASTROCLK exits, the
current Precision Time/Data Display window is saved; that window
will appear when Display Mode 8 is next selected.
When ASTROCLK is first executed, this mode shows Precision
Time Display #1 with all times shown to a precision of 0.0001
seconds. Note, however, that the displayed precision may be
greater than the accuracy of the calculations as discussed below.
The limitations of a microcomputer and the available
software become apparent as more complex calculations are
attempted. Given unlimited execution time and appropriate
software, of course, there is no reason why the microcomputer
cannot produce data to any desired accuracy. However, the real
world imposes certain constraints and the complex mathematics of
practical astronomy forces compromises. Even with a math
coprocessor, the calculation times are noticeable; without the
math coprocessor they are significant.
The Precision Data Displays show various intermediate
parameters required for the calculation of some of the basic
astronomical quantities. Each is an important item in its own
right, but in the context of a program such as ASTROCLK, its
function is more nearly that of the building block needed to
construct the whole. Readers are again reminded that the
precision of the displayed data is generally greater than its
accuracy; the higher precision has been retained as a testing
tool as the program's accuracy is gradually increased through
improved algorithms and technique.
The sample displays were all generated at 00:00:00 UT for
4 November 1988. The Daylight Flag was OFF and the Local
Coordinates were set for Calaveras County, near Sacramento, in
Northern California (preset location "CAL").
As an additional feature, the UP and DOWN arrow keys may be
used to increase or decrease the Julian Date by one day when
using the precision displays in Display Mode 8, but ONLY when the
clocks are OFF; use Function Key F4 to start and stop the
clocks. The UT time remains constant, but all other data are
recalculated. I have used this feature while comparing the
ASTROCLK calculations against tabulated data; how useful it may
otherwise be is questionable.
Precision Time Display #1:
--------------------------
UTC Coordinated Universal Time: 0:00:00.2404
UT Universal Time (=UT1): 0:00:00.0000
TAI International Atomic Time: 0:00:24.2404
TDT Terrestrial Dynamical Time: 0:00:56.4244
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 56
Gwich Mean Solar Time (UT): 0:00:00.0000
Greenwich App. Solar Time: 0:16:24.2747
GMST Grnwich Mean Sidereal Time: 2:57:45.7030
GAST Grnwich App. Sidereal Time: 2:57:45.9618
GSD Greenwich Sidereal Date: 2454172.123446
NOTES: For the period 1958 through 1971, A.1 USNO Atomic Time
will be shown in place of TAI International Time. Prior to 1984,
ET Ephemeris Time will be shown in place of TDT Terrestrial
Dynamical Time.
The basic time reference for all internal ASTROCLK time
calculations is Universal Time (UT), whether derived from the
computer's internal clock or entered manually. This time is
therefore considered to be exact and accurate to the full
precision shown and is the same as UT1.
Universal Coordinated Time (UTC), which is the time
broadcast by radio stations WWV, WWVH, and most other radio time
standards, is kept to within 0.9 seconds of UT by the occasional
insertion of Leap Seconds at the end of June or December. Except
for this Precision Time Display, which shows the calculated or
estimated difference between UT and UTC, ASTROCLK otherwise
assumes UT for all time calculations.
International Atomic Time (TAI) has been officially
recognized as an official time standard since 1972 although
the U.S. Naval Observatory has provided an atomic time standard
since 1958. The difference between TAI and UTC is published in
the Astronomical Almanac for years 1972 and up. For the period
1958 through 1971, ASTROCLK calculates USNO Atomic Time (A.1).
The difference between A.1 and UTC ranges from 0 to 10 seconds
and ASTROCLK assumes a linear rate of change with one second
increments added on January 1 or July 1 when appropriate. The
offset between TAI and A.1 versus TDT/ET is slightly different:
32.184 seconds versus 32.15 seconds respectively. Prior to 1958,
ASTROCLK does not display an atomic time.
Terrestrial Dynamical Time (TDT) and its pre-1984 cousin
Ephemeris Time (ET) are calculated for the period 1620 through
1989 based upon data published in the Astronomical Almanac.
Outside that period a formula by Meeus, adjusted slightly to
merge smoothly with the data in the Astronomical Almanac, has
been used (see BIBLIOGRAPHY). The Astronomical Almanac advises
that for most purposes ET and TDT may be considered a continuous
time standard. ASTROCLK uses the appropriate designation, ET or
TDT, depending upon the current date but otherwise makes no
distinction between them. Terrestrial Barycentric Time (TBT) is
never more than 1.7 milliseconds different from TDT and is not
shown; for most calculations the two may be considered the same.
ASTROCLK's calculation of Greenwich Mean Sidereal Time
(GMST) has been compared with the published Astronomical Almanac
data for the year 1988 and agrees to the full precision shown,
0.0001 seconds. However, Greenwich Apparent Sidereal Time (GAST)
involves many more calculations and the accuracy falls off to
approximately 0.01 seconds.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 57
Precision Time Display #2:
--------------------------
PST Local Standard Time: 16:00:00.0000
Local Mean Solar Time: 15:57:43.9999
Local App. Solar Time: 16:14:08.2747
LMST Local Mean Sidereal Time: 18:55:29.7029
LAST Local App. Sidereal Time: 18:55:29.9617
Equation of Time: + 0:16:24.2747
Delta T (TDT/ET-UT): 0:00:56.4244
Delta AT (TAI-UT): 0:00:24.0000
For locations within the United States as well as for other
areas falling in the same time zones, the abbreviation PST will
be replaced by the abbreviation appropriate for the local time
zone. In addition, the middle letter will change (S or D)
depending upon whether Standard or Daylight time is in effect, as
determined by the setting of the Daylight Flag. For other time
zones, the abbreviation PST will be replaced by LST (Local
Standard Time) or LDT (Local Daylight Time) according to the
setting of the Daylight Flag.
The local times shown have essentially the same accuracy as
the corresponding Universal or Sidereal times (given upon the
assumption that the local coordinates are exact). Thus, Local
Standard/Daylight Time may be considered exact (provided the
Daylight Flag and Zone Correction have been correctly set), Local
Mean Sidereal Time is accurate to the precision shown, and Local
Apparent Sidereal Time is accurate to approximately 0.01 seconds.
Local Mean Solar Time, calculated using UT and the local
longitude, is accurate to approximately the precision shown.
The Equation of Time is the difference between the Right
Ascension of the apparent Sun and the fictitious mean Sun. In
addition to being required for various calculations, it
represents the difference between mean solar time (upon which our
civil timekeeping is based) and apparent solar time, the time
shown by a sundial.
Delta T and Delta AT show the calculated or estimated
difference between UTC versus TDT/ET and TAI/A.1 respectively.
Prior to 1958, Delta AT is not shown. In ancient times, Delta T
can reach values greater than 24 hours; in this case, Delta T is
shown as days (suffixed by "d") followed by hours as usual. The
error in Delta T for ancient times is estimated to be as much as
several hours.
Precision Data Display #1:
--------------------------
Mean Obliquity of Ecliptic: 23 26'26.63" [0.02"]
True Obliquity of Ecliptic: 23 26'35.40" [0.02"]
Nutation in Longitude: 0 00'04.32" [0.05"]
Nutation in Obliquity: 0 00'08.76" [0.05"]
Equation of Equinoxes (secs): 0.263960 [0.005 sec]
e EARTH Eccentricity of Orbit: 0.01671380
L' MOON Mean Longitude: 157 55'15.39"
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 58
M' MOON Mean Anomaly: 168 35'33.91"
MOON Asc Node Longitude: 340 51'23.71"
E Equation of Time (h:m:s): + 0:16:25.8574
T Jul Cent @ 2000 JAN 1.5 TDT: -0.111581091
@ 1900 JAN 0.5 ET: 0.888418909
NOTES: All items are expressed in degrees or time as appropriate,
with the format determined by Function Key F7. In the actual
ASTROCLK display, the last parameter is shown with the omega
symbol usually associated with that parameter, and all items in
degrees include the degree symbol. Because of the differences
among printers, those symbols have been omitted in this text.
The numbers in the right hand column above are the
approximate accuracy of the calculations compared with data
published in the Astronomical Almanac. Items with no accuracy
data shown have been checked against other sources and appear to
be accurate to about 0.001 degrees or 0.1 seconds or better; the
MOON paramaters are used in the calculation of the first four
items of the precision times and therefore probably have at least
comparable accuracy. Function Key F7 may be used to change the
format of the displayed data as in other display modes. In the
default mode (degrees or hours, minutes, and seconds), data are
displayed to a precision of 0.01 seconds of arc or time.
Precision Data Display #2:
--------------------------
Geocentric Data @ Equator & Ecliptic of Date:
---------------------------------------------
L SUN Mean Longitude: 223 27'38.75"
0 SUN True Longitude: 221 47'42.02"
0a SUN Apparent Longitude: 221 47'27.20"
M SUN Mean Anomaly: 300 42'43.97"
v SUN True Anomaly: 299 02'53.02"
R SUN Radius Vector (AU): 0.99167759
C SUN Equation of Center: -1 39'50.95"
a SUN Apparent Rt. Ascension: 14:37:24.72
d SUN Apparent Declination: -15 22'27.89"
NOTES: All items are expressed in degrees or time as appropriate,
with the format determined by Function Key F7. In the actual
ASTROCLK display, Right Ascension and Declination are shown with
the alpha and delta symbols usually associated with those
parameters, and all items in degrees include the degree symbol.
This display shows the calculated values for parameters
associated with the Sun. CAUTION: Depending upon the source,
formulae used to calculate these and other precision data may
refer T to 2000 JAN 1.5 TDT, the new standard epoch, OR to 1900
JAN 0.5 ET, the prior standard epoch.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 59
Precision Data Display #3:
--------------------------
SUN Geocentric Rectangular Equatorial Coords
--------------------------------------------
@ Mean Equator & Equinox of Date:
X Coordinate: -0.7393294
Y Coordinate: -0.6063765
Z Coordinate: -0.2629145
@ Mean Equator & Equinox of J2000.0:
X Coordinate: -0.7375287
Y Coordinate: -0.6082189
Z Coordinate: -0.2637152
The standard equator and equinox shown in the sample is
J2000.0, and is always the same as that used for the internal
star database. It may be set with Function Key F8 to any desired
epoch using a variety of input formats. These coordinates are
frequently required for Epoch B1950.0 for use with planetary and
other solar system data. NASA also uses B1950.0 for most data.
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 60
PLANETARY DATA DISPLAYS
By far the most demanding task that ASTROCLK asks of the
micro-computer is the calculation of the positions of the
planets; it is also one of the more important tasks for the
interested star gazer, since the planets are among the more
distinctive objects easily seen with the naked eye. Beginning
with Version 8846, ASTROCLK calculates the full planetary
position at the current time (ecliptic and equinox of date),
displays its results using Display Mode 9, and makes those
results available to the Tracking Display, Display Mode 0. For a
micro-computer without a math coprocessor, the computational
delays are very significant; my Zenith Z-183, running at 8 Mhz,
requires about four to six seconds per position calculation,
depending upon the planet. For a micro-computer equipped with a
math coprocessor, the delays are noticeable but my Zenith Z-248
IBM AT-compatible gets the job done in less than one second.
When the letter "P" is pressed, or the first time Display
Mode 9 is requested, ASTROCLK asks you to select a planet or
minor planet for display. The major planets are assigned their
"standard" numbers corresponding to their position outward from
the Sun. Planet #3, the Earth, cannot be selected. A planet may
be selected by entering either the planet number or the planet
name. Except for Mercury and Mars, the first letter (upper or
lower case) of the planet name is sufficient to select the
planet; the first two letters are required to distinguish between
MErcury and MArs. The letter "H" will select Comet Halley, the
letter "X" will select the external Minor Planet Catalog (if
present), and the letter "Z" allows manual entry of all orbital
parameters. See the section MINOR PLANET SELECTION for additional
information on minor planets and orbital parameters. The Planet
Selection display reminds the user of the planet's numbers and
names:
PLANET SELECTION
----------------
Enter PLANET NAME/NUMBER:
1 = Mercury 6 = Saturn
2 = Venus 7 = Uranus
4 = Mars 8 = Neptune
5 = Jupiter 9 = Pluto
H = Comet Halley (internal data)
X = External Minor Planet Catalog
Z = Enter Orbital Parameters
- All orbital elements @ Mean Equinox of Date
- Use UP and DOWN arrows to change PLANET
after making initial selection.
Once the initial selection has been made or at any time from
another display mode, pressing "P" will allow you to select a
planet or minor planet and will automatically select Display Mode
9 unless you are in the Tracking Display, Display Mode 0. While
displaying planetary data in Display Mode 9, pressing the UP
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 61
arrow will cycle through the planets (but not the minor planets!)
moving outward from the Sun and pressing the DOWN arrow will
cycle through the planets moving inward toward the Sun.
The position of the selected planet is calculated in several
stages using the current time. First, current position data for
the Sun are calculated (as in the Precision Data Display), then
the orbital elements for all planets are determined for the
instant of interest. Next, the heliocentric (Sun-centered) and
geocentric (Earth-centered) ecliptic coordinates for the
requested planet are found and corrected for perturbations of the
other planets. Finally, the geocentric ecliptic coordinates are
converted to equatorial coordinates, the more familiar Right
Ascension and Declination. All data to this point are calculated
for the mean equinox of date, which appears as the Julian Epoch
at the right side of the window border for Display Mode 9 in the
form "[J1988.9]".
The internal star database is always referenced to a
particular epoch; the current star database epoch is always shown
in Display Mode 0. The default star database epoch is J2000.0 and
it may be changed using Function Key F8. For consistency,
therefore, the planetary equatorial coordinates are also
automatically precessed to the current star database epoch and
then preset as the current target for use in Display Mode 0, the
Tracking Display. Therefore, having determined the current
coordinates for the selected planet, the user may change to the
Tracking Display and monitor the planet's position in equatorial
and horizon (observer) coordinates. Selecting a planet from the
Tracking Display directly by pressing "P" bypasses the Planetary
Data Display and shows the tracking data immediately.
Once a planet has been selected by using "P" or Display Mode
9, the data is always available to the Tracking Display UNLESS
you select a star or other celestial object for display in the
meantime. If you have selected a star for display, you must again
select a planet with "P" before its data will be shown in the
Tracking Display.
Because of the additional computational delays for the
"average" micro-computer when processing a planet's equatorial
coordinates in the Tracking Display, Display Mode 0, the user may
notice a significant "slow down" in the Tracking Display as
compared to the performance when a star or other fixed celestial
object is being tracked. The additional calculations related to
planetary position are only performed when a planet is selected
for display.
Two display screens are available for the selected planet in
Display Mode 9: Planetary Data (default) and Orbital Data.
Pressing the PgUp, PgDn, or "9" keys will switch between the two
displays. The sample displays shown below were taken for MARS at
00:00 UT on 8 November 1988 and ASTROCLK's star epoch was
J2000.0. As with other ASTROCLK data, the reader is reminded that
the accuracy of the data is not necessarily as good as the
precision displayed; this is particularly true of the planetary
data, given the complexity of the calculations. See the section
PRECISION AND ACCURACY TESTS for additional discussion.
Because of the differences among printers, the degree symbol
(which appears on the displays) has been deleted from all sample
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 62
displays, and the symbols omega and theta zero have been deleted
for the Longitude of the Ascending Node and the Angular Diameter
at 1 AU, respectively, in the Orbital Display.
MARS Planetary Data [J1988.9]
-------------------------------------------------------
Heliocentric Longitude: 29 59'44.09"
Heliocentric Latitude: -0 37'00.40"
Heliocentric Radius (AU): 1.4320914
Appar Geocentric Longitude: 0 34'28.42"
Appar Geocentric Latitude: -1 36'23.79"
Geocentric Distance (AU): 0.5498746
Apparent Right Ascen [J1988.8]: 0:04:41.06
Apparent Declination [J1988.8]: -1 14'36.50"
Apparent Right Ascen [J2000.0]: 0:05:15.32
Apparent Declination [J2000.0]: -1 10'53.20"
Ang Size (") & Vis'l Mag: 17.02 -1.97
The Heliocentric Ecliptic Longitude, Heliocentric Ecliptic
Latitude, Heliocentric Radius, and Geocentric Distance are the
instantaneous values corrected for perturbations but not for
light time; they are therefore the true values for the given
instant. The Geocentric Ecliptic Longitude and Geocentric
Ecliptic Latitude have been corrected for perturbations, light
time, nutation, and aberration and are therefore the apparent
values for the given instant.
The two sets of equatorial coordinates, apparent right
ascension and apparent declination, are calculated for two
different epochs. The first set is calculated for the current
time and date and is therefore for the Mean Equinox of Date
(J1988.9 in the samples, also shown at the upper right of the
window border). The values for the second set of equatorial
coordinates have been precessed to the current epoch for
ASTROCLK's internal star database; the default epoch for the
internal star database is J2000.0, as shown in the sample above.
Precessing the internal star database using Function Key F8 will
change the epoch used for these coordinates. It is this last set
of coordinates, referenced to the current star database epoch,
which is automatically transferred to Display Mode 0, the
Tracking Display, where the same data is displayed, and is
converted to horizon coordinates and corrected for refraction.
The apparent size in arcseconds and the approximate visual
magnitude are shown on the last line of the display.
Care must be taken when comparing ASTROCLK's planetary data
with other sources to ensure that the data are calculated for the
same time, date, and epoch. For example: the Astronomical Almanac
and the USNO Floppy Almanac use Terrestrial Dynamical Time (TDT)
and provide positions as of the Mean Equinox of Date; Bretagnon
and Simon use UT (internally converted to TDT/ET) and calculate
positions as of the Mean Equinox of Date but use the Zero Year
date numbering system for years "BC"; Sky & Telescope Magazine
provides sample planetary data each month which is calculated
using Universal Time (0 hours UT) and the Mean Equinox of Date;
and, Astronomy Magazine does not specify a time scale or time for
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 63
its monthly planetary calculations but data is marked Epoch
J2000.0.
MARS Orbital Data [J1988.9]
-------------------------------------------------------
L Mean Longitude: 21 40'41.18"
_ Mean Daily Motion in Long: 0 31'26.65"
w Longitude of Perihelion: 335 51'13.93"
e Eccentricity: 0.09339464
i Inclination: 1 50'59.08"
Longitude of Asc Node: 49 28'17.35"
a Semi-Major Axis (AU): 1.52368830
Ang Diameter @ 1 AU (arcsecs) 9.36
Std Visual Magnitude [V(1.0)] -1.52
The Mean Longitude, Longitude of Perihelion, Eccentricity,
Inclination, Longitude of the Ascending Node, and the Semi-Major
Axis are the six standard orbital elements used for calculating
the instantaneous position of a planet in its orbit about the
Sun. [NOTE: Some authors use the Argument of the Perihelion
instead of the Longitude of the Perihelion.] The Mean Daily
Motion in Longitude is derived from the Mean Longitude as a
function of time. The Angular Diameter at 1 AU is the standard
angular diameter measured at a distance of 1 Astronomical Unit.
Similarly, the Standard Visual Magnitude shown is the standard
visual magnitude measured at a distance of 1 Astronomical Unit.
The calculation of the positional data for a selected
planet requires first that the orbital elements for all planets
be calculated. The orbital elements are then used to compute the
perturbations affecting the selected planet. Only the orbital
elements for the selected planet are shown in the Orbital Data
Display and only the last three items in the display are
constants. All other data must be re-computed for each instant.
After a planet has been selected, switching to the Tracking
Display, Display Mode 0, will show the usual tracking data for
the selected planet updated once per second or as rapidly as the
micro-processor can manage (degree symbol deleted):
P4 MARS (Automatic)
---------------------
EQUATORIAL COORDINATES [J2000.0]:
RIGHT ASCENSION (hours): 0:05:15.32
DECLINATION (degrees): -1 10'53.20"
HOUR ANGLE (hours): 19:10:42.68
APPARENT COORDINATES [J1988.8]:
RIGHT ASCENSION (hours): 0:04:41.06
DECLINATION (degrees): -1 14'36.52"
HOUR ANGLE (hours): 19:11:16.94
OBSERVER HORIZON COORDINATES:
ALTITUDE [Hc] (degrees): 14 01'20.61"
AZIMUTH [Zn] (degrees): 101 10'41.66"
Apparent ALTITUDE (degrees): 14 04'59.95"
[Charts SA=17 U=I/II-215] [VMag = -1.97]
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 64
MINOR PLANET SELECTION
The current complete Minor Planet Catalog as of this
writing, ELEM1989.001 for March 15, 1989 compiled by E. G. Bowell
of the Lowell Observatory, lists 3,774 minor planets and their
various orbital parameters. This is far too much data for direct
inclusion in ASTROCLK; in conventional ASCII format, the full
Minor Planet Catalog requires over 380K bytes of disk storage. In
addition, reading the ASCII data and converting the parameters to
the internal numerical formats required by ASTROCLK requires
extra computational time. I have therefore designed a compressed
Minor Planet Catalog format for use with ASTROCLK; the
compression to ASTROCLK's MPC format, along with data examination
and recreation of the original ASCII format, if desired, is
performed by program MPCAT. The resulting MPC format file,
ELEM891.MPC, requires approximately 241K bytes for the full
catalog, still quite a bit if you don't happen to be interested
in minor planets. Therefore, an abbreviated version of the full
catalog, ASTROCLK.MPC, containing the first 250 minor planets is
included with the standard distribution of ASTROCLK and only
requires approximately 64K bytes. The full MPC catalog is
available from my bulletin board system. (See A BRIEF EDITORIAL
for further information.)
Unlike the major planets, no "general theory" exists for the
complex motion of the many minor planets; these smaller bodies
are not only subject to the influence of the major planets but
interact with each other -- and there are thousands of them in
the so-called "asteroid belt". There are therefore no handy time-
dependent equations which will yield orbital and position
information over long time spans. Instead, so-called "osculating
elements", accurate for a specific date (the "epoch" of the data)
and referred to a specific ecliptic and equinox (the "standard
describe the orbit of each minor planet. Most minor planet data
is referenced to the standard epoch of B1950.0, although some
publications including the Astronomical Almanac now use J2000.0.
When processing minor planet data, ASTROCLK first reduces
the raw osculating elements as read from the Minor Planet Catalog
in use to the equinox of date (based upon the current epoch set
in ASTROCLK for the internal star database), then performs all of
the various orbit and position calculations as of the ecliptic
and equinox of date. The data is then processed in the same
manner as for the major planets, taking into account light time
and yielding the apparent position for the equinox of date. The
data are also precessed to the current standard epoch, but
readers are cautioned that these data are also the APPARENT
position rather than the ASTROMETRIC position. In particular, the
Astronomical Almanac data for selected minor planets (Section G)
are astrometric as of Epoch J2000.0 and will therefore not agree
precisely with those generated by ASTROCLK.
As the date of interest moves further from the catalog date,
the position calculations become progressively less accurate.
When possible, use a minor planet catalog which is valid for a
date near (within several months, for example) the date of
interest. ASTROCLK displays the osculation date for the external
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 65
catalog in the form DD-MM-YYYY, but no check is made for
excessive time spans. See also the section PRECISION AND ACCURACY
TESTS for further discussion.
Before attempting to use the Minor Planet Catalog, use
Function Key ALT-F10 to verify that the path and file name for
the catalog are set correctly. Particularly if you are upgrading
from a previous version of ASTROCLK, the file name and path will
probably be incorrect. As with the major planets, selection of a
minor planet begins by pressing the letter "P" for Planet
Selection, then press "X" to select the Minor Planet Catalog.
Information about the catalog is then displayed and the minor
planet number is requested:
MINOR PLANET SELECTION
Minor Planet SOURCE file: ELEM1989.001
[SOURCE: E G BOWELL, LOWELL OBSERVATORY]
Minor Planet CATALOG file: ASTROCLK.MPC
Minor Planet Data Date: 15-03-1989
Minor Planet Ecliptic Date: B1950.0
First Minor Planet: 1
Last Minor Planet: 250
Total Minor Planets: 250
Enter Minor Planet NUMBER:
[Press RETURN to enter NAME]
Enter the desired minor planet number, followed by RETURN, or
press RETURN alone and receive the prompt to enter the minor
planet name:
Enter Minor Planet NAME:
[Press RETURN to cancel]
Enter the desired minor planet name, followed by RETURN, or press
RETURN again to cancel the name request and return to the main
Minor Planet Selection menu. When entering a minor planet name,
upper or lower case may be used and only sufficient letters are
required to unambiguously identify the desired minor planet. For
example, to search for VICTORIA you might enter simply "VIC" or
"vic". ASTROCLK will search the catalog for any minor planets
whose name begins with the letters VIC.
When possible, use the minor planet NUMBER rather than the
minor planet NAME. ASTROCLK can retrieve the data directly when
the number is given, but must search through the entire file
looking for a match to the name. Depending upon the type and
speed of your disk system, the time difference can be very
considerable!
Once ASTROCLK has located the requested minor planet or one
which matches the requested name, the data for that minor planet
is displayed:
Minor Planet 12: VICTORIA
Ecliptic Epoch: B1950.0
Orbital Elements Date: 15-03-1989
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 66
M Mean Anomaly: 334.29342
w Argument of Perihelion: 68.76240
Long of Ascending Node: 235.12759
i Inclination: 8.37950
e Eccentricity: 0.21976110
a Semi-Major Axis: 2.33431886 AU
B Std Blue Magnitude @ 1AU: 7.23
If a minor planet number was requested, the following prompt will
also appear:
Press RETURN to ACCEPT, SPACE to cancel:
As indicated, press RETURN to accept the minor planet or press
SPACE to return to the main Minor Planet Selection menu. If a
minor planet name was requested, the following prompt will appear
instead:
Press RETURN to ACCEPT, SPACE to continue:
If this is the desired minor planet, press RETURN to accept it.
If you wish ASTROCLK to search further for another match to the
requested name, press SPACE. The process will continue until a
minor planet is accepted or until the end of the catalog has been
reached.
Once accepted, the minor planet data is treated in almost
the same manner as that for a major planet. The positional data
will be automatically displayed, unless Display Mode 0 was
selected (degree symbol omitted):
VICTORIA Positional Data [J1989.1]
[Osculating elements as of 1989 MAR 15]
Heliocentric Longitude: 252 37'40.34"
Heliocentric Latitude: 2 32'11.13"
Heliocentric Radius (AU): 1.9520963
Appar Geocentric Longitude: 275 40'38.95"
Appar Geocentric Latitude: 2 02'35.38"
Geocentric Distance (AU): 2.4224614
Apparent Right Ascen [J1989.1]: 18:24:21.39
Apparent Declination [J1989.1]: -21 16'48.43"
Apparent Right Ascen [J2000.0]: 18:25:00.46
Apparent Declination [J2000.0]: -21 16'25.01"
Blue Photographic Magnitude [B]: 10.65
Pressing "9" will display the orbital data. (NOTE: The pi and
omega symbols associated with Longitude of the Perihelion and
Longitude of the Ascending Node, as well as the degree symbol,
have been omitted from this text but appear on the display.)
VICTORIA Orbital Data [J1989.1]
[Osculating elements as of 1989 MAR 15]
M Mean Anomaly: 326 33'52.52"
L Mean Longitude: 271 00'02.48"
n Mean Daily Motion in Long: 0 16'34.86"
Longitude of Perihelion: 304 26'09.94"
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 67
w Argument of Perihelion: 68 43'54.29"
e Eccentricity: 0.21976110
i Inclination: 8 22'37.22"
Longitude of Ascending Node: 235 42'15.65"
a Semi-Major Axis (AU): 2.33431886
q Perihelion Distance (AU): 1.82132638
T Perihelion Date: 1985 NOV 21.338043
[B = 7.23]
Pressing "0" will select the Tracking Display, as usual, and the
data for the minor planet will have been automatically
transferred as with the major planets. The tracking data display
corresponding to the minor planet VICTORIA indicates the usual
data with the prefix "MP #nn", where "nn" is the Minor Planet
Number as read from the Minor Planet Catalog. A parenthetical
reminder that the data originated with the Minor Planet Catalog
is included. The following sample illustrates the data presented:
MP #12 - VICTORIA (MP Catalog)
EQUATORIAL COORDINATES [J2000.0]:
RIGHT ASCENSION (hours): 18:25:00.46
DECLINATION (degrees): -21 16'24.98"
HOUR ANGLE (hours): 7:55:04.82
APPARENT COORDINATES [J1989.1]:
RIGHT ASCENSION (hours): 18:24:21.39
DECLINATION (degrees): -21 16'48.43"
HOUR ANGLE (hours): 7:55:43.90
OBSERVER HORIZON COORDINATES:
ALTITUDE [Hc] (degrees): -35 21'31.90"
AZIMUTH [Zn] (degrees): 269 30'45.70"
Apparent ALTITUDE (degrees): -35 21'31.90"
[Charts SA=22 U=II-339] [BMag = 10.65]
Entering Orbital Parameters
You may also enter the orbital parameters for an orbiting
body directly. The orbital parameters are the same as those used
for the minor planets. In this case, use the "Z" selection on the
planet selection menu. The following data are required:
Object Name
Ecliptic Epoch
Elements Date (D,M,Y)
M Mean Anomaly
w Argument of Perihelion
Long of Ascending Node
i Inclination
e Eccentricity
a Semi-Major Axis
B Std Blue Mag @ 1AU
In order to determine an elliptical orbit, six orbital
parameters are required, often referred to as "osculating
ASTROCLK Astronomical Clock and Celestial Tracking Program Page 68
elements". To these are added the ecliptic date of the data (to
determine the coordinate system used) and the date of the
parameters. Since this function is patterned after the minor
planet function, the standard blue photographic magnitude
measured at one Astronomical Unit is also requested.
Each item shown in the list above will be requested in turn.
The Object Name may be entered in upper or lower case letters but
will be converted to all upper case letters by ASTROCLK. For most
minor planets and similar bodies, the Ecliptic Epoch is B1950;
enter the epoch as either Besselian or Julian, designated by the
letter prefix "B" or "J" (upper or lower case) respectively,
followed by the full epoch year and optional decimal fraction
(e.g. B1950.0). The Elements Date is the date for which the
orbital parameters are accurate; enter as day-month-year or by
any of the other date formats used with Function Key F3;
regardless of the input format used (calendar date, julian date,
epoch, etc.), ASTROCLK will convert the information to standard
calendar date. The position of an orbiting body may generally be
calculated for dates within a few months of the date of the
orbital parameters and still retain reasonable accuracy.
Once all of the orbital parameters and other data have been
entered, they will be displayed again, as interpreted by
ASTROCLK, along with the following message:
Press RETURN to ACCEPT, SPACE to cancel:
If the data are correct, press RETURN; if not, press the SPACE
BAR and the data will be discarded. Operation from this point is
identical with normal minor planet selection above.