eli5: When analysing light spectrum of distant galaxies, how do we know if its red shift, AND NOT just the actual color of galaxy?

Question

since different gases give different color when burning, how can we know that the red colour we obtained is not just the actual color of gases burning, but rather a red shift?

In: 3

Answer 1

Gases produce very very specific bands as plasma. For instance, hydrogen produces 656.46nm light. We call this H-alpha. We can calibrate our redshift predictions based upon how much these lines shift.

Also, it’s not ‘burning’, just very hot.