light-year
Sign in to saveA 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
Article
8 sectionsContents
- Definitions
- History
- Usage of term
- Related units
- See also
- Notes
- References
- External links
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.
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.