17 upvotes, 4 direct replies (showing 4)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
If I were floating out in deep space and I stuck my hands out in front of me, would I see them? Or would everything be black?
Comment by [deleted] at 27/04/2023 at 03:04 UTC
7 upvotes, 0 direct replies
[deleted]
Comment by Andromeda321 at 27/04/2023 at 03:07 UTC
6 upvotes, 0 direct replies
I suppose the question is what you mean by deep space. Even if you were, say, between the Andromeda and Milky Way galaxies, you would manage to see an outline of your hands over pitch darkness (after a long period of letting your eyes adjust). But there are voids that are bigger where this would be much more challenging!
In our own galaxy, if you’re floating close enough to a star you’d probably see them just fine. However if you were in a very dense nebula, you wouldn’t see them because all the light would be blocked.
Comment by SonOfOnett at 27/04/2023 at 03:18 UTC
4 upvotes, 1 direct replies
Our eyes perceive objects by having light bounce off that object and into our eyes. Studies seem to show that human eyes can detect as few as ~10 photons. I doubt you would call that "seeing" your hand though, just being more right than not that it was there is you guessed. And those photons need to be in the visible spectrum for our eyes to detect them though. In earth orbit there is clearly plenty of light for this to work since we can see on earth. Even much farther out in the solar system there are plenty of visible spectrum photons for us to see our hands in front of us.
So, deep space. The average photon density of the universe (which corresponds to deep space) is reasonably high at ~few hundred per cm^3, but the problem is most of those photons are not detectable by the human eye since they are not in the visible spectrum. I'm having trouble finding a good data source to get a better answer, but there's so little stuff in general in the universe that its likely close enough to pitch black in the darkest places in the universe (far from any galaxy) that it would be similar to being in a cave with little spots of light being distant galaxies. Your hand would be visible by blocking those pin-prinks of light
Comment by Fit-Personality-6549 at 17/06/2023 at 23:58 UTC
1 upvotes, 0 direct replies
Huh? It depends on light 🤡