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Originally Posted by Potironette

So..the dark blue I see at night is actually bits of blue light arriving from the other side of the planet :o?

Yes, exactly. If the atmosphere wasn't there, it would be completely black. Pictures taken from the moon support this.

Also, just a sort of random question out of curiosity: when a light in a room turns on, does the light actually travel/move to fill up the space or does everything just magically light up at once?

Neither! Light doesn't fill space. When you turn the light on, the bulb begins to emit photons. Those photons bounce off of the things in the room and you see the ones that end up ricocheting into your eyes.

But yes, objects closer to the light source will be hit with photons before objects farther away from it.

Or, if I have a laser on top of one hill hitting a mirror over 186,282 miles away angled to hit some surface beside me, will there be a delay in my seeing that surface?

This experiment has actually been carried out for real!

When they visited the moon, astronauts left behind a retroreflector on the surface. (Retroreflectors are the things like on street signs and bicycles that are textured so that no matter what angle incoming light hits the surface, at least some of it is sure to bounce towards your eyes.) If you have a powerful enough laser (it has to be powerful because the atmosphere is going to make it spread out and lose energy), and you shine it at that retroreflector, you won't see it light up for about 2.5 seconds. (Actually, you won't SEE it light up at all because the reflection is so weak by the time it gets back here, but it's measurable by instruments.)

This technique has given us a VERY precise figure on EXACTLY how far the moon is from the earth -- and how fast it's spiraling away from the planet (about 3.8cm/year).

Actually, this is probably a badly thought out question and stuff will take the time of light speed--and it just looks like a dark room fills up with light at once because light speed is so fast, and rooms so small.

No such thing as a bad question. It shows you're exploring the problem space and seeing what else there is to be found.

Though regarding the dark room, light speed isn't actually the only factor involved. The bulb itself takes time to warm up and start emitting light in the first place. So if it feels instant between hitting the switch and seeing things, that's just a sign of how bad humans are at perceiving very small intervals of time.

I have a math review problem (midterms are coming up) that asks me to find a factor of (j-3)^2 - (k-5)^2 but I'm not sure how to do it. I tried to expand it, but just got j^2 - 6j - 16 - k^2 + 10k and it doesn't seem useful. Should I have expanded it at all?

Nope, you shouldn't have expanded it. It's a formula you should have memorized already: a^2 - b^2 = (a + b)(a - b)