As defined by the International Astronomical Union (IAU), a light-year ( or light year) is the distance that light travels in a vacuum in one Julian year. The speed of light is 299,792,458 metres per second. Therefore, a light-year (symbol: ly) is a unit of length, equal to just under 10 kilometres.
The light-year is often used to measure distances to stars and other distances on a galactic scale, especially in non-specialist and popular science ...
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As defined by the International Astronomical Union (IAU), a light-year ( or light year) is the distance that light travels in a vacuum in one Julian year. The speed of light is 299,792,458 metres per second. Therefore, a light-year (symbol: ly) is a unit of length, equal to just under 10 kilometres.
The light-year is often used to measure distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The preferred unit in astrometry is the parsec, because it can be more easily derived from, and compared with, observational data. The parsec is defined as the distance at which an object will appear to move one arcsecond of parallax when the observer moves one astronomical unit perpendicular to the line of sight to the observer, and is equal to approximately 3.26 light-years.
The related unit of the light-month, roughly one-twelfth of a light-year, is also used occasionally for approximate measures.
A light-year is equal to:
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