2.5 million light-years
The largest of the galaxies visible with the naked eye, Andromeda is a vast spiral similar in shape to the Milky Way. By using ultraviolet light, astronomers can highlight the structure - blue colours represent the far ultraviolet light given off by brilliant young stars in the spiral arms, while orange tones are from near ultraviolet given off by the older, cooler stars in the galaxy's core.
Credit: Image made in ultraviolet light by the Galaxy Evolution Explorer Team for NASA / JPL-Caltech.
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