ASTRON 2B03 Lecture Notes - Lecture 6: Cosmic Distance Ladder, Blueshift, Raisin Bread
28 Aug 2016
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Lookback time: the time it takes for light from a distant galaxy to travel to us, when it gets here can see the galaxy. See the galaxy as it was that long ago. if galaxy is a million lightyears away, see galaxy as it appeared a million years ago. Within our own galaxy times are relatively short, don"t really worry about it. Oooh pretty galaxy probably won"t change much over 30 million years. Lookback time is usually 100-1000s of years, not as big a deal, another galaxy is 12 million lightyears away center of milky way is about 25000 years ago. 1 lightyear is distance light travels in 1 year, about 9450000000000km. Lookback times are measures in years, 1 year = 1 lightyear. Lookback time is a unit of time, lightyears is a unit of distance. In the 1930s, it was discovered that galaxies are getting further apart from each other as time goes on, the universe is expanding.
