How do we know what the universe looks like if we are seeing stars as they appeared millions of years ago?

Answer 1

your right

we DONT know what most of it looks like in this exact moment in time.

we see them as they were back then (as long as it takes the light to get from there to here)
the closer things we look at look "fresher" than those far far away

http://www.youtube.com/watch?v=mcBV-cXVWFw

Answer 2

What astronomers study is called the visible universe. Various methods are used to determine star and galaxy distances. The farthest visible galaxies have been calculated to be about 13.7 billion light years away.

It is true that we are seeing is light from where those farthest galaxies were 13.7 billion years ago. They have been moving out from that spot for another 13.7 billion years. The rate of the expansion of the universe is extrapolated to determine the size that the universe would be TODAY. Right now, the diameter of the universe is 92.94 billion light years across. We know what the universe looks like because we also know from measurements of the expansion of space.

Not all galaxies are that far away either. Some are as close as 2 million light years. Some stars are as close as 4.3 light years.

Here is a diagram of what the universe probably looks like.

http://www.ldps.ws/Mirror/Universe/index.html

Answer 3

Some good answers here, but let me just clarify something. We do not see stars as they were millions of years ago. It is the galaxies we see as they were millions and even billions of years ago.

The farther stars in our galaxy are perhaps 100,000 light years away.

Answer 4

Stars last so much longer than mere millions of years that the difference is not that important. But for studies of distant galaxies astronomers do take the time delay into account.

Answer 5

Depends on what you mean by "looks like". We really can't know what it looks like in the sense that you are proposing. In truth, you cannot separate time and space. So what the universe looks like really depends on the observer. We have NO WAY of knowing if M87 collapsed "today" (in our reference frame) because of the spacetime separating us. So it has no meaning in terms of reality. If we were observing from a different location - any different location - then the universe would look different. There is no such thing as a "master observation point" from which you can see everything as it occurs.

Answer 6

We can see it only as it was when light left the radiating bodies. Scientists know how to tell when that happened.