What is Hubble's law?
A) The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.
B) The recession velocity of a galaxy is directly proportional to its distance from us.
C) The recession velocity of a galaxy is inversely proportional to its distance from us.
D) The faster a spiral galaxy's rotation speed, the more luminous it is.
E) The faster a spiral galaxy's rotation speed, the less luminous it is.