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light-year
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View of the Andromeda Galaxy (Messier 31, M31).
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light-year

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News •

Largest celestial object of its kind discovered in the distant universe • Feb. 14, 2025, 12:56 AM ET (CNN)

light-year, in astronomy, the distance traveled by light moving in a vacuum in the course of one year, at its accepted velocity of 299,792,458 metres per second (186,282 miles per second). A light-year equals about 9.46073 × 1012 km (5.87863 × 1012 miles), or 63,241 astronomical units. About 3.262 light-years equal one parsec.

This article was most recently revised and updated by Erik Gregersen.