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*Subject*: Re: [amsat-bb] Earth-Moon distance*From*: Norm McMillan <njmcmillan@xxxxxxxxxxx>*Date*: Sat, 23 Oct 1999 07:55:22 +1000

John Gibson wrote: > > 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 The error is less than 1%!!! Considering the Earth as an oblate sphere and the moons orbit as not truly circular would probably account for the difference. But then, I'm not an orbital mechanic!!!!! Norm VK2XCI ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**References**:**Earth-Moon distance***From:*John Gibson

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