light-year

Also known as ly, light year, lightyear, l.y., light-years, lightyears, light years

A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Despite its inclusion of the word "year", the term is not a unit of time.

AI overview

A light-year is a unit of distance—not time—that measures how far light travels through empty space in one year, equal to about 9.46 trillion kilometers. Astronomers use light-years to describe the enormous distances between stars and galaxies because these distances are too vast to express conveniently in kilometers or miles.

AI-generated from the Wikipedia summary — may contain errors.

Key facts

Unit.name: light-year
Unit.standard: astronomy units
Unit.quantity: length
Unit.symbol: ly
Unit.units1: metric (SI) units
Unit.units2: imperial and US units
Unit.units3: astronomical units
Unit.caption: Map showing stars and star systems lying within 12.5 light-years of the Sun
Unit.image: 300px

via Wikipedia infobox

Described at

Lichtjahr - Lexikon der Physik

Lichtjahr, Einheitenzeichen Lj, in der Astronomie übliche Einheit für Entfernungen. 1 Lichtjahr ist die Entfernung, die ein Lichtsignal wä…

spektrum.de →

Link to a page describing this subject · 22,573 chars · not written by Vinony

Wikidata facts

Image: 1e16m comparison 10 light years sirius.png

Show 6 more facts

unit symbol: a.l.
conversion to SI unit: 9460730472580800
conversion to standard unit: 63240
Wikidata SPARQL query equivalent: wd:Q531 p:P2370/psn:P2370 [wikibase:quantityAmount ?source; wikibase:quantityUnit ?base]. ?item p:P2370/psn:P2370 [wikibase:quantityAmount ?target; wikibase:quantityUnit ?base]. BIND(?source / ?target as ?value)
described at URL: www.spektrum.de/lexikon/physik/lichtjahr/9014
Commons category: Light-year

Sources (6)

via Wikidata · CC0

~11 min read

Article

8 sections

Contents

Definitions
History
Usage of term
Related units
See also
Notes
References
External links

The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist contexts and popular science publications. The unit most commonly used in professional astronomy is the parsec (pc), approximately 3.26 light-years.