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Hubble's Constant and Distance to M31
You now know that you need two pieces of information in order to use
Hubble's Law to solve for M31's velocity: the distance to M31 and Hubble's
constant.
Looking up "distance to M31" on the web, it is easy to find that the
Andromeda galaxy (the other name for M31) is 2,900,000 light years away.
Wow! That seems like a long way, but actually the Andromeda galaxy is one
of our nearby neighbors! The value of Hubble's constant, H0,
was vigorously sought in the 20th century. It was determined in the
early 21st century independently by the Hubble Space Telescope and
the Wilkenson Microwave Anisotropy Probe to be 72 km/sec/Mpc.
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