Doppler Effect
posted by Fernandez .
How fast must we be approaching a distant galaxy emitting yellow light (590nm) for it to appear green (520nm)?
I believe it uses doppler effect, but how?

for nonrelativistic speeds, we can use the approximation.
c/520 = (1+v/c) * c/590
520(1+v/c) = 590
1+v/c = 59/52
v/c = 7/52
v = 7/52 c
Is that relativistic? Generally, less than 0.1c is considered nonrelativistic, so we may be a bit off, but if that matters, use the exact formula, which you can find with a quick web search.
Not being sure just how the Doppler effect is calculated, I just did some online searches. You could also have done this.