system
Given the following post, respond as if you're commenting on Reddit:
human
How do astronomers know the "red shift" is coming from the Doppler effect and not from static stars producing light at a red wavelength?

Would scientists not need a benchmark to know what wavelength the star is emitting and then what it is received at? If so, how do they determine the emitted wavelength?
gpt
They measure the full spectrum of light. Each element creates a distinct ‘absorption’ line on the spectrograph. When you look at a red-shifted Star,  all the elements are there in the right relationship to each other, it’s just that the entire spectrum is shifted towards the red.