If a galaxy is 500 Mly away from us, how fast do we expect it to be moving and in what direction?
This is College Physics Answers with Shaun Dychko. Hubble discovered that the velocity with which another galaxy is receding away from us is approximately equal to this Hubble constant times the distance from us to the galaxy. We are told that the galaxy is 500 megalight years away and the Hubble constant is 20 kilometers per second per megalight year. So we multiply 20 by 500, the megalight years cancel leaving us with units of kilometers per second and that is 1.0 times 10 to the 4 kilometers per second away from us is the speed of the galaxy.