Light-year

A light-year, alternatively spelled light year (ly or lyr), is a <a href="/facts/Unit_of_length/C8XqXetI">unit of length</a> used to express <a href="/facts/Astronomical_distance/EYsRSlep">astronomical distances</a> and is equal to exactly 9460730472580.8 km, which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the <a href="/facts/International_Astronomical_Union/GMFPImXo">International Astronomical Union</a> (IAU), a light-year is the distance that <a href="/facts/Speed_of_light/sKSQwdNx">light travels in vacuum</a> in one <a href="/facts/Julian_year_(astronomy)/EVdRNUe3">Julian year</a> (365.25 days). Despite its inclusion of the word "year", the term should not be misinterpreted as a <a href="/facts/Unit_of_time/L9ShSGBv">unit of time</a>.
The light-year is most often used when expressing distances to stars and other distances on a <a href="/facts/Galaxy/zCyUvEf7">galactic</a> scale, especially in <a href="/facts/Public_understanding_of_science/144nmXhX">non-specialist</a> contexts and <a href="/facts/Popular_science/cnhLw9rI">popular science</a> publications. The unit most commonly used in professional <a href="/facts/Astronomy/0ArJVM1p">astronomy</a> is the <a href="/facts/Parsec/SwSsk57J">parsec</a> (symbol: pc, about 3.26 light-years).

Light-year open-in-new

Light-year