in astronomy, the systematic displacement of individual lines in the spectrum
of a celestial object toward the blue, or shorter wavelength, end of the visible spectrum. The amount of displacement is a function of the object's relative velocity toward the observer. Most observed blue shifts are the result of the Doppler effect
. The blue shift is the opposite of the red shift
. Blue shifted celestial bodies are quite rare. Of the billions of known galaxies, only about 100, including the Andromeda
galaxy, are blue shifted.
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