Blueshift is a phenomenon in which the light emitted by an object appears to be shifted to shorter wavelengths, or towards the blue end of the spectrum. In the case of galaxies, blueshift refers to the observation that the spectral lines in the galaxy's light appear to be shifted towards the blue end of the spectrum. This indicates that the galaxy is moving towards us, and the amount of blueshift can be used to calculate the velocity at which the galaxy is approaching us. This is known as the Doppler effect, named after the physicist Christian Doppler who first described this phenomenon in 1842.
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