Does the blue shift of the Andromeda Galaxy contradict Big Bang cosmology?
No. The motions of all galaxies consists of the part of their motion produced by local gravitational influences, and a part determined by cosmological expansion. The typical velocity of galaxies within their clusters, such as the Milky Way and the Andromeda Galaxy, is about 200 – 1000 kilometers per second. The cosmological expansion effect increases at the rate of about 75 kilometers per second per megaparsecs. This means that at a distance of 2.5 to 3 mega parsecs, the galaxies random motion within its cluster ( say 200 kilometers per second) is about as large as its cosmological redshift. When you add these velocities together, you could get any speed from 0 to 400 kilometers per second. For nearer galaxies such as the Andromeda Galaxy, its random velocity is larger tan its cosmological redshift so you can get blue shifts! This is why astronomers have to look at very distant galaxies so that they can easily see the cosmological redshift above the random speeds of the galaxies in the
