A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance that light travels in a vacuum in one year. While there is no authoritative decision on which year is used, the International Astronomical Union (IAU) recommends the Julian year. Numerical value A light-year is equal to: · 9,460,730,472,580.8 km (about 9.461 Pm) · 5,878,625,373,183.61 statute miles · about 63,241 astronomical units · about 0.3066 parsecs The exact length of the light-year depends on the length of the reference year used in the calculation, and there is no wide consensus on the reference to be used. The figures above are based on a reference year of exactly 365.25 days (each of exactly 86,400 SI seconds). This is the value recommended by the IAU. However, other reference years are often used (e.g.

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