how many miles in a light year wiki
Light-year The light-year is a unit of length used to express astronomical distances. It is about 9.5 trillion kilometres or 5.9 trillion miles.[note 1] 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).[2] Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.
Speed of light In 1972, using the laser interferometer method and the new definitions, a group at the US National Bureau of Standards in Boulder, Colorado determined the speed of light in vacuum to be c = 7008299792456200000♠299792456.2±1.1 m/s. This was 100 times less uncertain than the previously accepted value. The remaining uncertainty was mainly related to the definition of the metre.[Note 11][109] As similar experiments found comparable results for c, the 15th General Conference on Weights and Measures in 1975 recommended using the value 7008299792458000000♠299792458 m/s for the speed of light.[145]