Cosmos


COSMOS - The SAO Encyclopedia of Astronomy › L

Light Year


  • The light year is a unit of distance that comes from the knowledge that light (or electromagnetic radiation in general) takes a finite length of time to travel through space. It is defined as the distance that light travels in a year through a vacuum.

    The speed of light in a vacuum= 299,792,458 metres/second
    The number of seconds in a year=60 × 60 x 24 × 365.25
    1 light year or ly= 60 × 60 x 24 × 365.25 × 299,792,458
    = 9.46 × 1015 m
    = 9.46 × 1012 km
    = 63,240 AU
    = 0.306 pc

    Remember that a light year is not a measure of time!


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