How Can We Measure Redshift Using the Spectrum of a Star?

[Phys12]

As far as I know, when we use the spectrum of a star, we see where the absorption lines are and using this, we can detect the elements that are present in the star. We also measure whether those absorption lines are supposed to be for a particular element. But why is it not possible that the star contains a different element altogether because the absorption lines are in a different place instead of the spectrum being redshifted/blueshifted?

Thanks!

 

[Jonathan Scott]

The relative strengths and the relative spacing of spectral features provide a lot of information which can be used to help identify them. You can match the patterns with other known stars to work out the redshift.

 

[Phys12]

The relative strengths and the relative spacing of spectral features provide a lot of information which can be used to help identify them. You can match the patterns with other known stars to work out the redshift.

Oh, so it's because we look at the entire pattern, got it. So, if it were the case, that we looked at just one absorption line (because that's all that we'd have), then we couldn't determine the redshift/blueshift, right?

 

[Jonathan Scott]

Oh, so it's because we look at the entire pattern, got it. So, if it were the case, that we looked at just one absorption line (because that's all that we'd have), then we couldn't determine the redshift/blueshift, right?

We also have clues from the intensity distribution of the spectrum even where there are no clear lines, and if there was only one line it might well be the strongest expected one for that type of object, but certainly the more detail the easier it is to be sure.