20.2 Measuring Galactic Distances Radar ranging – radio waves are transmitted from Earth and bounced off Venus. This is used to measure AU Standard Candles – light source of known luminosity. Use stars similar to Sun which has similar L to the sun. Parallax is used to measure few hundred light years Standard candles for most cosmic distance measurements Sun like standard candles are not useful for above 1000 LY away Main sequence fitting is determining distances by comparing main sequence in different star clusters. Its better to do main sequence fitting over 1 star comparing because it reduces uncertainty through testing through many stars Cepheid variables Main sequence fitting doesn’t work for measuring distances to other galaxies.
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