ASTRON 2B03 Lecture Notes - Lecture 3: Eardrum, Spectroscopy, Barcode
6 Dec 2017
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Something in 10s of 1000s of years ago is within our galaxy** The lookback times for these galaxies range from many millions to billions of years. At last, we begin to see changes compared with nearby galaxies. Looking outward in space, we inevitably look back in time, we see things as they were long ago. Distances measured in lightyears (or parsecs: 1 light year = distance light travels in 1 year. = 9 460 000 000 000 km: lookback times measured in years. 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. Instead find recognizable, familiar objects in a galaxy (e. g. stars or nebulae) whose properties we already know.
