From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00, PP_MIME_FAKE_ASCII_TEXT autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII X-Google-Thread: 103376,c212e60d58417232 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2004-03-14 09:27:27 PST Path: archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.icl.net!proxad.net!freenix!nnx.oleane.net!oleane!news.agarik.com!news.agarik.com!teleglobe.net!teleglobe.net!62.81.31.29.MISMATCH!cyclone.auna.com!twister.auna.com!53ab2750!not-for-mail From: Jano Newsgroups: comp.lang.ada Subject: Re: [OT] Hints for an algorithm - avoiding O(n^2) Message-ID: References: <5d6fdb61.0403120115.7c102e3c@posting.google.com> <7j5s2c.32r.ln@skymaster> <1Yi4c.85891$dP1.243229@newsc.telia.net> X-Newsreader: MicroPlanet Gravity v2.50 Date: Sun, 14 Mar 2004 18:27:21 +0100 NNTP-Posting-Host: 212.97.168.186 X-Trace: twister.auna.com 1079285245 212.97.168.186 (Sun, 14 Mar 2004 18:27:25 MET) NNTP-Posting-Date: Sun, 14 Mar 2004 18:27:25 MET Organization: AUNA TLC Xref: archiver1.google.com comp.lang.ada:6321 Date: 2004-03-14T18:27:21+01:00 List-Id: Robert I. Eachus dice... > Bj�rn Persson wrote: > > > I didn't mean to say that the Sun doesn't affect the Moon. "If what J-P > > wrote were true, the Moon would not orbit both the Sun and the Earth, as > > it does, but only orbit the solar system's center of gravity (if we > > ignore the rest of the universe)." Is that better? > > > > You can't choose your words too carefully when there are Ada language > > lawyers in the audience. :-) > > I think you missed my point. Earth's moon is unique in the solar > system. It is the only moon whose path around the Sun doesn't cross > itself. In fact, the effect of the Earth's gravity is so slight that if > you are calculating the Moon's orbit, it is better to compute it the > same way as other planets. (Treat it as orbiting the sun, with > perturbations by the gravity from other planets. For all other moons, > you are better off calculating them as orbiting some planet, with the > Sun's gravitational effect as a perturbation.) I had never stopped to think about it, but if I understand you correctly, that means that the Moon's orbit has a zig-zag path. Nice :) I'll look further into your Runge-Kutta suggestion, thanks.