light year

(ly)
   a unit of distance used in astronomy. One light year is the distance that light travels in one year through a vacuum (and, of course, most of the Universe is close to being a vacuum). In the official definition of the International Astronomical Union, the light year is based on the Julian year of exactly 365.25 days or 31 557 600 seconds and the defined speed of light c = 299,792,458 meters per second. Thus one light year equals exactly 9 460 730 472 580.8 kilometers, or 9 460 730 472 580 800 meters. One light year is approximately 5.880 trillion miles.

Dictionary of units of measurement. 2015.

Look at other dictionaries:

  • Light year — Light year, Light year Light year (Astron.) 1. The distance over which light can travel in a year s time in a vacuum, 5.88 trillion miles (9.46 trillion kilometers); used as a unit in expressing stellar distances. It is more than 63,000 times as… …   The Collaborative International Dictionary of English

  • Light-year — Light year, Light year Light year (Astron.) 1. The distance over which light can travel in a year s time in a vacuum, 5.88 trillion miles (9.46 trillion kilometers); used as a unit in expressing stellar distances. It is more than 63,000 times as… …   The Collaborative International Dictionary of English

  • light year — also light year, lightyear, distance light travels in one year, 1888, from LIGHT (Cf. light) (n.) + YEAR (Cf. year) …   Etymology dictionary

  • light year — n 1.) the distance that light travels in one year, about 9,460,000,000,000 kilometres, used for measuring distances between stars ▪ a star 3,000 light years from earth 2.) light years ahead/better etc than sth informal much more advanced, much… …   Dictionary of contemporary English

  • light year — light years 1) N COUNT A light year is the distance that light travels in a year. ...a star system millions of light years away. 2) N COUNT: usu pl, N prep/adv (emphasis) You can say that two things are light years apart to emphasize a very great …   English dictionary

  • light-year — [līt′yir΄] n. 1. Astron. a unit of distance equal to the distance that light travels in a vacuum in one year, c. 9,460,000,000,000 km (5,880,000,000,000 mi): abbrev. lt yr or ly: cf. PARSEC 2. a very great distance, amount of time, etc.usually… …   English World dictionary

  • light year — light ,year noun 1. ) count the distance that light travels in a year, used as a unit for measuring distances in space 2. ) light years plural INFORMAL a very long way in time, distance, or quality: Her life in Hollywood was light years away from …   Usage of the words and phrases in modern English

  • light-year — light′ year n. 1) astron. the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances 2) cvb light years a) a very great distance, esp. in development or… …   From formal English to slang

  • light year — ► NOUN Astronomy ▪ a unit of distance equivalent to the distance that light travels in one year, 9.4607 x 1012 km (nearly 6 million million miles) …   English terms dictionary

  • Light-year — For other uses, see Light year (disambiguation). Image showing the scale of a light year (outer shell) and a light month (inner shell) surrounding the Sun compared to Comet 1910 A1 s orbit (yellow line) and Comet Hyakutake s orbit (orange line).… …   Wikipedia

  • light-year — noun the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers • Syn: ↑light year • Hypernyms: ↑astronomy unit • Part Meronyms: ↑light hour, ↑light minute, ↑light second …   Useful english dictionary

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