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Light-hour

A '''light-hour''' (also written '''light hour''') is a Units of measurement|unit of length. It is the distance travelled by light in vacuum in one hour. Based on the current definition of the metre a light-hour is equal to 1e12 m|1,079,252,848,800 metres (~1.08 Tm). That is about 7.214 Astronomical unit|au. This distance can easily be related to the speed of light in kilometres per hour, since light travels 1,079,252,848,800 m every hour, or 1,079,252,848.8 km/h. To give an example, the semi-major axis of Pluto (planet)|Pluto's orbit's is about 5.473 light-hours.

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