Light-year
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 Γ 1012 km (5.87863 Γ 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.
Citation Information
Article Title:
Light-year
Website Name:
Encyclopaedia Britannica
Publisher:
Encyclopaedia Britannica, Inc.
Date Published:
10 November 2026
Access Date:
November 13, 2026