Glossary term: Light Year

Description: A light year is a unit of length sometimes used in astronomy to express large astronomical distances like distances to stars or between galaxies. It is defined as the distance that light travels in vacuum in one year: 9.46 trillion kilometers (km), that is 9.5x1012 km. By using the unit "light year", the large distances become numerically more manageable: the nearest star to the Sun is 40 trillion km away or more simply 4.25 light years. Astronomers also use the units light minutes or light hours: light takes about eight minutes to get from the Sun to Earth and about four hours to get to Neptune. Light year is a rarely used term in astronomical research where the parsec (approximately 3.26 light years) is the preferred measure of distance.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".