ASTRON 2B03 Lecture Notes - Lecture 6: Before Present, Cosmic Distance Ladder, Blueshift
12 Oct 2018
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If something happens in the milky way (a star explodes) we will not see it until many years later when the light reaches us. If something happens in a galaxy far away, it can take millions of years for us to know about it! Has it changed much: recall that (cid:498)it(cid:499) is made of billions of stars, each of which is very long-lived, tiny details different, but galaxy (cid:498)lifetimes(cid:499) are billions of years long. We see things as they were long ago. Distances measured in lightyears (or pasecs: 1 light year= distance light travels in 1 year= 9 460 000 000 000 km. In the 1930s, it was discovered that galaxies are getting farther apart from each other as time goes on. Two things needed to be measured: distances to other galaxies. Can we use parallax, like we used for stars: no much too far away.
