Velocity determination through redshift

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Astronomers determine the velocity of distant stars by measuring the redshift of their light, which involves analyzing the star's spectrum. Each element emits a unique pattern of spectral lines, known as a "fingerprint," that can be shifted due to the Doppler effect. By comparing the observed positions of these lines to their expected positions, astronomers can identify the extent of the redshift. For example, if hydrogen lines appear closer to the red end of the spectrum, it indicates that the light has been redshifted. This measurement allows astronomers to calculate the star's velocity relative to Earth.
ShayanJ
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As you know,astronomers calculate the velocity of distant stars by measuring their light's redshift.This suggests that they have a way to know each star's light's wavelength in a different way from observing its light.What is that way?
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They measure the shift in the star's spectrum. Each element produces a unique "fingerprint" as a pattern of lines in the spectrum. By looking at the position of these lines in the star's spectrum they can tell if they have been shifted from their normal position, this tells them the amount of red shift.

For Instance, if they find the pattern of lines associated with hydrogen closer to the red end of the spectrum than it should be, this tells then that the light has been red shifted. How far it has moved tells them by how much it has been red shifted.
 

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