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Lines in the optical spectrum o a supercluster o distant galaxies (richt), as compared tae absorption lines in the optical spectrum o the Sun (left). Arraes indicate reidshift. Wavelenth increases up taewart the reid an beyond (frequency decreases).

In pheesics, reidshift happens when licht or ither electromagnetic radiation frae an object is increased in wavelenth, or shiftit tae the reid end o the spectrum.