04-17-2013, 03:30 PM | #21 |
Join Date: May 2005
Location: Oz
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Re: Meson alternatives?
Conservation of angular momentum requires a planet's north and south poles to point in constant directions. As its orbit carries a planet around a star, the direction to the star is constantly changing. Therefore the north pole of a planet cannot point constantly at the star (or any of the stars) in its system — because of conservation of angular momentum.
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04-17-2013, 03:31 PM | #22 |
Join Date: Sep 2007
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Re: Meson alternatives?
Angular momentum is a vector quantity. If Dinom's north pole points at its primary as it revolves, then the direction of that angular momentum changes by 180 degress in half its orbit, pointing in the opposite direction from which it started, and then changes again, reversing itself twice per orbit -- all without any external force acting on the planet.
Or think of the planet as a gyroscope. The pole isn't going to change where it's pointed relative to "the fixed stars" unless something pushes on it. If the north point points at the primary at 0 degrees in the orbit, then at 180, it should be pointing directly away from the primary. Conservation of angular momentum means you can't just go from L to -L back to L. You're stuck at a constant L unless you have a way to dump 2L onto some other body, and get it back later. |
04-17-2013, 03:32 PM | #23 | |
Join Date: Dec 2007
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Re: Meson alternatives?
Quote:
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04-17-2013, 03:40 PM | #24 |
Join Date: Sep 2007
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Re: Meson alternatives?
Yes, by about 50 arc seconds per year, or 26000 years to return back to its starting position. This precession is due to the fact that the Earth's rotational axis is tilted WRT its orbit, and also that it's a bit oblate. Tidal forces from the Sun thus torque the planet a little bit.
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04-17-2013, 04:03 PM | #25 |
Join Date: May 2005
Location: Oz
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Re: Meson alternatives?
Yes, owing to the effect of tidal torques on Earth's tidal and equatorial bulges, which transfer angular momentum between Earth's rotation, its orbit, and the orbit of the Moon; the orientation of Earth's axis precesses with a period of 25,700 years.
Yes, Dinom might well be precessing too. If it were rotating rapidly, if it were close to its star, and if it had a large moon in close it might precess several times faster than Earth. No, there is no way it could precess around an entire great circle of the sky with a period equal to its year.
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Decay is inherent in all composite things. Nod head. Get treat. Last edited by Agemegos; 04-17-2013 at 04:07 PM. |
04-17-2013, 04:41 PM | #26 | |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Meson alternatives?
Quote:
As far as Dinom goes, pretty sure that's atmosphere code E, ellipsoid, from CT. |
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04-17-2013, 04:48 PM | #27 | |
Join Date: Sep 2007
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Re: Meson alternatives?
Quote:
What's wrong with Youghal? Just the scale of the effect (from "too thin" to "comfortable")? |
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04-17-2013, 04:52 PM | #28 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Meson alternatives?
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04-17-2013, 05:31 PM | #29 | |
Join Date: Aug 2004
Location: Copenhagen, Denmark
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Re: Meson alternatives?
Quote:
I've no idea if that's any better. A 1600 year orbit sounds as if it's quite a distance from the star. Can it really burn that bright at that distance? But it is at least different."The revolution of Dinom around its central star means that the polar axis will not always point towards the star. The 1600 year orbit of Dinom advances the pole about one degree in four years; in 200 years, it will advance 45 degrees. Hans |
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04-17-2013, 05:58 PM | #30 | |
Join Date: May 2005
Location: Oz
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Re: Meson alternatives?
Quote:
That leaves, I guess, the proposition that the land surface might not conform to the geoid (the water surface has to if it's connected), but that's inconsistent with hydrostatic equilibrium in the mantle, and it would correct itself in only thousands to about 20,000 years. I suppose that it's possible that there might have been truly enormous ice-caps that weighed down the polar regions and displaced mantle material to under the topics. If such caps melted very recently (in the last couple of thousand years) then I suppose that the planet might be in the midst of adjusting from a large-scale disequilibrium. But then I think you would expect to see large polar oceans and equatorial land-masses, with the oceans about as deep as the highlands are elevated. There would be progressive flooding of the equatorial land as it sank towards equilibrium, and vigorous seismicity. Even so, I feel intuitively that the amount of ice necessary to make this effect noticeable to the extent implied is implausible. I'll have to ask a geophysicist about that. In any case, this situation is hardly compatible with there being any land at the poles.
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Decay is inherent in all composite things. Nod head. Get treat. Last edited by Agemegos; 04-17-2013 at 06:08 PM. |
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meson, nuclear damper, radiation |
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