MadSci Network: Astronomy

Re: Is there 1 known planet whose solar days are longer than its year?

Date: Wed Apr 4 00:43:11 2001
Posted By: James Kopchains, Secondary School Teacher, Earth Science, Woodside Intermediate School 125
Area of science: Astronomy
ID: 985316786.As

   The only planet that we know of that has a longer solar day than solar 
year is Earth's sister planet Venus.  The Venusian solar day (the time it 
takes the planet to spin once on its axis) is the equivalent of 243 Earth 
solar days.  Its year (or period of its revolution around the sun)  is 
equal to 224.7 Earth days.  As a result, the surface of Venus sees a 
sunrise and a sunset approximately 117 days apart.  Most of the planets in 
our solar system have a solar day far shorter than its year, though 
Mercury comes close to Venus (solar day = 59 Earth days; year = 88 days).  
At present, it is difficult to determine the rate of rotation on planets 
found outside our solar system, but none have been found that has a longer 
day than year like Venus.

   All information taken from the book, "Space Encyclopedia" by Heather 
Couper and Nigel Henbest for DK Publishing.

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