What do astronomers mean when they say that looking at the stars is like looking back in time?

Question

This question was in my textbook. Can someone PLEASE explain?

Answer 1

No matter what you look at you are seeing that event in the past.

  Even a person in the same room with you,you are seeing them as the existed hundreds of millionths of a second in the past.

  The farther you move away from them the older the image you receive of them.

  Though you are completely isolated from them in time your reaction time allows you to interact with them as though no time isolation existed.

Answer 2

If a star is 10 lightyears away, that means when we finally see the light from that star, it has taken 10 years to get here ergo we are seeing the star as it was 10 years ago

Answer 3

I'm not sure..I guess it's because the stars have been there forever, long before we have.

Answer 4

The finite speed of light. It takes a certain amount of time for light to travel from a source to any point (like your retina). The more distant the source then the more time required before you will 'see' it. It will be as it appeared in its past further and further as the distance increases between your eye and that source.

Answer 5

The reason why astronomers refer to "Looking back in time" has to do with two concepts, one is the distance to the star and the speed of light.

When you turn on a light in your room, although you can not tell you see the light a fraction of a second after the light actually turned on. Light does not move infinitely fast, it takes time to cross distances. It travels very fast however, around 300,000 kilometers a second.

However, space is very large and it actually takes light some amount of time to cross it. For instance, the sun is pretty far away, so far that it takes light which travels 300,000 kilometers a second, over 8 minutes to get here.

So essentially you see the sun always 8 minutes ago. If you were to look at the sun right now, you are seeing the sun as the light left its surface 8 minutes ago. If you want to see what the sun actually looked like at the moment you looked at it, you will have to wait another 8 minutes.

Now other stars are very far away it can take many years for their light to reach us, so you are looking back in time because you see the star as it was however long ago it takes the light to cross the distance from it to earth.

Answer 6

On the scale of the universe, light travels slowly.

When we look at a star, we see it as it was when the light left it.

If the star is at 100 light-years, it means we see it as it was 100 years ago.  100 light-years is right next door.

The furthest stars we can see with the naked eye are about a few thousand light-years.

The furthest object that most people can see in a dark sky is the Andromeda galaxy.  It is 2.4 million light-years away.  We see it as it was 2,400,000 years ago.

It is part of the "Local Group".  There are things we see in telescopes that are billions of light-years away.  Of course, we see them as they were billions of years ago.

Looking at anything, is looking back in time, because you see it as it was in the past, not as it is "now".

Even our Sun:  499 seconds (a little over 8 minutes)

Answer 7

Because, the moment they see the star, they immediately come to think that they see the light  released millions of years ago from that star. Suppose you live in a star and look back to the earth now. What you see on earth from there: Possibly you see the ice age...no mankind.