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Old September 15 2012, 10:48 PM   #44
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Re: About planetary gravity

Technically, only the Earth travels in the ecliptic plane. It's called that because it's the plane where eclipses happen, where the Moon passes directly between the Earth and the Sun -- which, naturally, would correspond to the plane of the Earth's motion around the Sun. Naturally the Moon doesn't orbit exactly in the ecliptic (it's off by about 5 degrees), or there'd be a solar eclipse every four weeks and a lunar eclipse midway between each one. And all the other planets' orbital planes range from about 3/4 of a degree (Uranus) to over 7 degrees (Mercury) off of the ecliptic.
Written Worlds -- Christopher L. Bennett's blog and webpage
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