Question

A star is observed moving away from Earth. What can you conclude about the spectrum of that star?

Answer 1

The light will be red-shifted, there's a doppler shift due to the star travelling away from us.

Answer 2

Well what do you know about redshift and blueshifts? Red light has a much longer wavelength and lower energy than blue light, and this is where the idea comes from.

A source that's emitting a wave will have a certain wavelength, and if the source moves towards or away from you, it'll either cause the waves to be pushed together or seem stretched apart even though it's still emitted at the same rate.

Answer 3

The two responses above me are correct. I just want to clarify that a "red shift" is actually just a shift to a lower frequency of light. And a "blue shift" is the opposite, it's a shift to a higher frequency! They're named this because visible light will shift towards blue in the spectrum or red.

But this means all light can shift (I think). Food for thought; if a red light had a strong red shift, or a blue light had a strong blue shift, we wouldn't be able to see those lights.

(Same is true for any visible light, but a red and blue are at the ends of the visible spectrum and so smaller shifts are sufficient.)