A light second is a unit of length. It is defined as the distance light travels in an absolute vacuum in one second or 299 792 458 metres. Note that this value is exact, since the metre is actually defined in terms of the light second. It is just over 186,282 miles and almost 10⁹ feet.

A light minute is 60 light seconds and a light hour is 60 light minutes or 3600 light seconds. A light year is 31,557,600 light seconds.

Some distances in light seconds:

• The mean diameter of the Earth is 0.0425 light seconds.
• The average distance from the Earth to the Moon is 1.282 light seconds.
• The diameter of the Sun is about 4.643 light seconds.
• The average distance from the Earth to the Sun (or 1 astronomical unit) is 499.0 light seconds or 8.317 light minutes.

See also: speed of light

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