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*Subject*: [amsat-bb] Earth-Moon distance*From*: John Gibson <GIBSON@xxxxxxxx>*Date*: Fri, 22 Oct 1999 11:03:18 -0400 (EDT)

This question is addressed to those on the list (e.g. G3RUH, W3IWI, etc.) who are experienced and wise about orbital mechanics. It is not exactly amateur satellite stuff, but I expect to find more wisdom on this list than elsewhere. I am working up a set of orbits notes for use in an introductory college physics course. One of our exercises is calculating the orbital period of a two-body system. The usual equation, assuming circular orbits, is (please excuse the clunky mathematical notation): T*T = (2*pi)*(2*pi)*r*r*r/G(M+m). My problem is making this equation give good results when I apply it to the Earth-Moon system. The correct average period should be 27.322 days, but this answer requires r = 384,750 km. This is not satisfactory, because every reference lists the mean Earth-Moon distance as 384,400 km. Am I expecting too much from this simple formula? Can someone show me my error or point me to some good references? John Gibson no8V@amsat.org ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**Re: Earth-Moon distance***From:*Norm McMillan

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