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What I mean is, can a planet orbiting its sun have a fixed rotational axis relative to the sun ie in the case of earth the tilt is like this /........(sun)......./. as it goes around the sun. Can a planet have a tilt that works like this: \.......(sun)......./. as it goes around its sun. where / and \ are the axial tilt of said planet.

Edit: Rephrased the question is: Can a planet's precession frequency match its orbital frequency?

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  • $\begingroup$ I don't really understand, sorry! I suggest to insert some image to make your question more clear, if you can! $\endgroup$ – user259412 Apr 6 '15 at 0:07
  • $\begingroup$ I think he's asking if a planet can do the same thing our moon does. (One side always faces us.) $\endgroup$ – CoilKid Apr 6 '15 at 2:00
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For a conventional planet (i.e. one that is self gravitationally round), conservation of the planet's angular momentum makes this impossible (except for the trivial case of the axis perpendicular to the orbital plane.

A non-spherical planet with a tilted axis will precess under the influence of tidal forces. It takes the earth about 26,000 years to go through one precession cycle. I don't know if there is a geometry that would make the precession frequency match the orbital frequency and would have to look into some textbooks to derive an expression for the necessary conditions.

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  • $\begingroup$ This is exactly what I was asking for thanks, I have put an edit in my question so that it is more clear based on your wording. $\endgroup$ – Gordon Muscat Apr 6 '15 at 12:14
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Figure out a planet in orbit of 360 degree. You would have a 45 degree axis at start and -45 degree axis at mid course of this planet around the orbit. It would means that this planet would have taken a speed or inclined throughout that course implying that from Her own, it developed a way to tilt like around an ice cream cone. This could means that a centifugal center point is exerting less influence on Herself. Like the Olympic discipline Hammerthrowing with a full and a non-fully tense cable, or a sort of reactive influence on the planet. I guess We could agree about a tidal force or cosmic friction that would affect the course of an orbit and creates an obligatory tilt, that planet scraping Herself on asteroids, on radioactive clouds on other obstacles not yet to be discovered. Like our winds and tides, matter doesnt have the choice in regards of gravity. Like the 8th electron getting hazed.

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