# Observing light

## Main Question or Discussion Point

If you were on the moon looking at the earth, why can you not see light between the earth and the sun? Same goes for heat. Why is the space between the sun and the earth so cold. Does light and heat only exist once it interacts with something else?
If light is a particle wouldnt the particles spread out to the point where you would have no idea what of where an object is. If light is a wave wouldn't we see sunlight cover everytinhg in every direction?

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Interesting question. If light was shining through a volume of space with no identifiable source, thus causing you to not be able to see anything...that would be kind of funny. It could be because light is characteristic of a source. At the moment, I think the only thing we know that light interacts with other than itself (in a sense) is matter.

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Matterwave
Gold Member
There is nothing to scatter the light back at you. Think of light rays. The light rays that go towards Earth only hit Earth. They don't want to come to you on the Moon.

You can't "heat" empty space. There is nothing to "heat". There can be background radiation, like the CMBR, but that's only about 3K. The only reason we get to see the CMBR everywhere is that the big bang happened "everywhere".

There is nothing to scatter the light back at you. Think of light rays. The light rays that go towards Earth only hit Earth. They don't want to come to you on the Moon.

Yes, that is the point I am trying to make. How can Photons enter the eye from light that is not directed towards it. If a lazer beam is shot across and infront of you it's photons do not travel towards you eye.

Why do we think that light always have to travel. Can in not travel and also be contained, like a sun. Not all light travels to your eye. Rather our observation travels to the light. Hard to explain, sorry.

russ_watters
Mentor
Yes, that is the point I am trying to make. How can Photons enter the eye from light that is not directed towards it.
They can't. Your eye can only detect photons that hit it and since photons travel in a straight line....
If a lazer beam is shot across and infront of you it's photons do not travel towards you eye.
Correct - unless they hit something and scatter toward you.
Why do we think that light always have to travel. Can in not travel and also be contained, like a sun. Not all light travels to your eye. Rather our observation travels to the light. Hard to explain, sorry.
That doesn't make sense...which is probably why it is wrong!

I am still curious how light travels from a distant star to our eyes. If light was a particle wouldnt the particles be spread out to much by the time it reached us? if it was a wave wouldnt we see a wall of light and not be able to tell where the star is? Wouldnt it be like seeing a wave from the shore, you would not be able to tell where the wave originated?

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