ASTRON 2B03 Lecture 6: Astron 2BO3 Lecture 6
18 Mar 2016
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Lookback time: the time needed for light to travel to us from a distant galaxy. Therefore we are seeing that galaxy as it was that long ago, as long ago as its lookback time is. Light travels at a nite speed, and it takes time to get to us. If something happens in a galaxy far away it can take millions of years for us to know about it. Something from andromeda galaxy is three million light years away, so seeing anything from that is how it was 3 million years ago. This galaxy is made of billions of stars, each of which is very long lived and changes slowly. It probs didn"t change much, tiny details may be different but galaxy live billions of years. Lookback times for stars in our own galaxy may be hundreds or maybe thousands of years. Looking outward in space, we inevitably look back in time.
