<p>what would happen to the time of sunrise and sunset if there was not an atmosphere?</p>
<p>My first thought was that we wouldn’t get all the reds and oranges and pinks we see during sunrise/sunset. I thought those were caused by the atmosphere, but you can investigate more :P</p>
<p>How are sunrise and sunset defined? First sign of light, or sun being completely in view?</p>
<p>That is an excellent question. I may be totally off-base here, because I’m speculating and have no idea on the matter, but since the atmosphere is what disperses the colors in the first place, odds are the sky would be fully white/yellow. White, I believe. Everything else = normal?
Anyone care to confirm/deny this?</p>
<p>It’d be what it looks like from the moon.</p>
<p>Imagine seeing the sun from outer space. Now imagine part of it cut off by a horizon.</p>
<p>If you’re asking just about the time, then if ‘time of sunrise’ is defined as the time a ground observer would see the sun (any fraction of it greater than 0), assuming the earth to be perfectly spherical (no mountains) and the only obstacle occluding the ground observer’s view (no buildings), I think the ground observer in the presence of the current atmosphere would see it a little earlier owing to the ‘downward’ refraction of light rays due to decreasing optical density of air moving ‘upward’ (‘upward’ and ‘downward’ being radially away from and toward the center of the earth respectively). So without atmosphere, it would be a little later.</p>
<p>Note: This is just a my theory - we’d have to analyse it empirically (somehow remove earth’s atmosphere? O_o) for a proper answer.</p>
<p>@Jimmy797: I think the ‘sky’ would be black, like what it would look like from the moon, observing that the Earth without atmosphere is equivalent to a larger moon for the purposes of our question.</p>
<p>Ah yes. I just took that light=white so you’d see that. But then again space = black.
It’s a good question. Can anyone refute my theory completely? I know that black is the right answer here but why wouldn’t you see it as bright white light?</p>
<p>It would look kind of like the lunar landing picture. Except with a big sun. And lots of lens flare.</p>
<p>@Jimmy797: Because the sun’s light is emitted from a spherical surface outside (and pretty far away from) the Earth, not a hollow spherical surface around the Earth. The colour of the ‘sky’ and the observed colour of the sun’s light are different things. You see the blue sky not due to dispersion but due to scattering. The colour of the sky is the colour of the light that is scattered by the particles in the air, because that would change their trajectory (their normal trajectory being away from the sun, not into your eyes - only those light rays you see when you look directly at the sun are an exception to this).</p>
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Because lack of visible light radiation on the retina makes ‘black’.</p>