I had a question. I did a problem where a distant galaxy emitted light that had a wavelength of A. On earth, the light had a wavelength of B. B ended up being greater than A. The question asked if the galaxy was receding from the earth or approaching the earth. The answer turned out to be the galaxy is receding from the earth. I'm not sure I understand why though. I do understand that the frequency of light is less on earth than in the galaxy, but get a little lost after that.