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Originally Posted by Celestial Mechanic
Come on, Warren, get serious! Celestial mechanics have not believed in crystal spheres, gears, pulleys, "mainsprings" and "escapement mechanisms" as the cause of celestial motions since the time of Copernicus.
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Well, I didn't mean it literally.
Quote:
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Newtonian gravitation is sufficient to explain the precession of the equinox. My precessional dialogues that I am always linking to calculated only the main lunisolar terms of the precession and got within 0.2 percent of the measured value. I was off by this amount not because of neglected causes such as the planets and higher order moments, but because in the interest of brevity and keeping the discussion elementary I ignored the eccentricities of the Earth and Moon, the inclination of the Moon's orbit, and the variational inequalities in the Moon's orbit. I hope to carry out a calculation soon that will take these into account as far as the squares of these small quantities and I expect to get within a tenth of a second of arc per century just from this alone. The contributions from the planets, relativity, and higher order moments are quite small. The flitting about of the Solar System barycenter is entirely irrelevant to the matter of precession.
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You're the expert, of course, and so I'm almost positive that you (and
Hornblower) are correct and that me and
Robert have got it wrong. But let me get this straight: You're hoping to nail down the precession to within a tenth of a second of arc per century without taking the planets into account at all? Because I found this paper on
Earth nutation theory (RESOLUTION B3: ON NON-RIGID EARTH NUTATION THEORY proposed by Joint Discussion N. 3 and endorsing the conclusions of the IAU-IUGG Working Group of The XXIIIrd International Astronomical Union General Assembly) where down toward the bottom, they recommended that when developing more refined models, "the perturbing bodies to be considered: in addition to the Moon and the Sun, the direct planetary effects of Venus, Jupiter, Mars, and Saturn, should be included."
Granted, nutation and precession are different processes; but aren't they related? If so, wouldn't it be possible for nutations to have tiny effects on the precessional period?