How can we see something millions of light years away?

[jayrandom]

Originally Posted by Follower Of X

pointless wise crack remarks were intended for the ones who make them first. nobody has to respond to my thread but when I ask a question I am looking for answers. "Science told me" or "it says so on the internet" might not be good enough for me.... you added further and I found what I was looking for. If you sit and really think about "seeing something billions of light years away" you can understand why i'd ask such a question. Here on earth our visibility is limited and it's no where near billions of light years so anyone with a slight bit of intelligence has the right to ask the question. Its all about distance.

It's fine to ask questions, but when multiple people take the time to answer your questions you can't continue to protest that no one answers them. If you don't understand the answers ask for clarification, but don't expect much sympathy if you don't try to understand. Even if you don't like the answers that are given, understanding where they come from can help you better state what it is exactly that you find objectionable.

[SD4020]

Things were explained as rudimentarily as possible. We have tried to break it down for you.

[cjg5]

Stars are brilliantly bright, burning balls of gas that are hundreds of thousands to millions of miles across. Get a few hundred billion of these stars together into a galaxy, and just think of their combined light output! How could we NOT see it? (Most "stars" we see in the night sky are actually entire galaxies).

[stycotl]

Originally Posted by Follower Of X

This has nothing to do with how old something is. It has to do with how far it is.

it has everything to do with it. how far away it is determines how old the light is that you are seeing from it.

let's look at two different stars from the big dipper, ursa major, as an example: mizar (and alcor along with it since it is a binary star system), which form the crest of the dipper's arced handle, and alkaid, which forms the end of the handle.



both of them look pretty similar in the sky, right?

mizar (and alcor) are about 83 ly away. that means that light takes 83 years to get from mizar to earth.

alkaid on the other hand is approximately 103.9 ly away, meaning that it takes almost 21 years longer for light to get from alkaid to earth than it does to get from mizar to earth.

in effect, what this means is that from our perspective, alkaid is farther behind mizar and alcor, even though they look like they are more or less on the same plane.

some other notable stars to look at:

proxima centauri (in Centaurus) is only 4.22 or 4.24 ly away. pretty darn close.

Proxima Centauri - Wikipedia, the free encyclopedia

mu cephei (in cepheus) is approximately 5,000 to 6,000 ly, and believed by some astronomers to be the farthest star visible to the unaided human eye. mu cephei's light takes thousands of years to get to us, putting it much farther back than either mizar or alkaid, even though it still looks like it sits at about the same distance on our visual plane. one of the reasons that we can see this star despite its distance is because it is also believed to be one of the biggest stars that we can see without a telescope.

Mu Cephei - Wikipedia, the free encyclopedia

Distance to Stars

Originally Posted by Follower Of X

Has the light reached the earth? or are we zooming in on light that hasn't gotten here?

as others have noted, we can only see light that has reached us.

going back to the earlier star examples, the light that you see at night from alkaid left that star about 104 years ago, whereas the light you see from mu cephei––reaching your eye at the same time––left that enormous star 500 to 1,500 years before khufu had the great pyramid of giza built in egypt in 2,500 BC.

note the "reaching your eye at the same time" part. the light actually has to contact the photoreceptor cells in your eyeball's retina in order for you to see it. so it had to come all the way from alkaid, mu cephei, mizar, or any of the others, and touch your eye in order for you to see it.

If we are seeing something billions of light years away it should be closer than it actually is because as you say we are viewing its light, where it that? Wouldn't it have to be somewhere in between? or closer than where it actually is?

Again if something is billions of light years away we see it, however we see its light so its actually closer and what is behind it is farther... is that what you are saying?

ashville's question to you about the railroad tracks is valid. it doesn't matter how far away it looks to your vision. it matters how far away it actually is.

another example would be your own eyes compared to an eagle's eyes. some eagles have vision three to five times more powerful than our own. so if you were standing 100 feet away from a rabbit, you wouldn't see very much detail. but the eagle, even if it was 200 feet away, would see the rabbit more clearly than you would. it could count the rabbit's whiskers if it knew how to count.

still, the eagle is twice as far away from the rabbit as you. being able to see it more clearly did not magically bring the rabbit closer to the eagle, or make the light reflected from the rabbit to the eagle's eyes move any faster. it can just see that light better than a human's naked eye can.

same with telescopes.

hope this helps.