The Sun, the Moon, and ... the Earth

[Joel S. Berson]

At 11/6/2010 08:59 PM, Garson O'Toole wrote:
>Below is a question from the textbook "Physics, classical and modern":
>The magnitude of the force on the moon due to the sun is more than
>twice the magnitude of the force on the moon due to the earth. Would
>it be more accurate to say that the moon orbits the sun rather than
>the moon orbits the earth?
>
>http://books.google.com/books?id=gt3iAAAAMAAJ&q=%22moon+orbits%22#search_anchor

OK, Garson -- but what's the *answer*?

>I do not know if astronomical nomenclature dictates an answer. With
>multiple objects the simple notion of "orbit" breaks down from my
>non-astronomer layperson perspective.
>
>"You got me circling like the moon around the sun!"
>
>There is a possible generous interpretation: You have me so
>dumbfounded that I am circling around you with a wobbling orbit as if
>I have a large companion object.

Otherwise known as the "three-body problem"[1] ... or, colloquially,
"three's a crowd".  Especially if the unwanted third is a large body.

[1] "Historically, the first specific three-body problem to receive
extended study was the one involving the Moon, the Earth and the
Sun.[citation needed]" [Wikipedia, which however goes on cite
Newton's "Principia."]

Joel

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