Science Fair Project Encyclopedia
Light day
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A light day (also written light-day) is a unit of length. It is defined as the distance light travels in an absolute vacuum in one day (of 86,400 seconds) or 25,902,068,371,200 metres (~26 Tm).
Note that this value is exact, since the metre is actually defined in terms of the speed of light. The light day isn't very frequently used at all since there are few astronomical objects or distances of that magnitude; the Oort cloud, for example, is thought to extend between 290 and 580 light-days out from the Sun.
See also: astronomical unit parsec
10-26-2009 08:16:03
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The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details