Timeline for Are there any known planets whose axis is oriented such that one pole always faces its star?
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| Sep 20, 2016 at 18:53 | comment | added | zephyr | @userLTK You can decompose any vector you want, but my point was, that your proposal of decomposing the rotation into two ways like that resulted in a scenario that didn't fit into the confines of the question. What's more, it was physically impossible as having the pole pointing towards the planet would mean you wouldn't be tidally locked anymore so you'd have no mechanism for causing that "second axis" of rotation. | |
| Sep 20, 2016 at 18:49 | comment | added | userLTK | @zephyr But you are right on the axis and pole. In my answer, the same part of the planet pointing towards the star, so I did miss that part. The pole couldn't because the pole is by definition on the axis of rotation. | |
| Sep 20, 2016 at 18:40 | comment | added | userLTK | @zephyr So your saying a 45 degree axis of rotation can't be divided into a 90 degree and a 0 degree of equal magnitude? The math gets pretty complicated, but I'd like verification on that because I don't see why you couldn't. See this question here: math.stackexchange.com/questions/1258051/… It's not a "second" axis of rotation it's one axis, but you're looking at it from an X and a Y axis so to speak. | |
| Sep 20, 2016 at 13:06 | comment | added | zephyr | @userLTK For one thing, you can't just combine two disparate rotations into a single axis of rotation. Rotation doesn't work like that. For another thing, even if you could add second axis of rotation which caused a different net axis, that axis would no longer be pointing directly at the planet (or stay pointing at the planet throughout the orbit) which means your scenario doesn't fit LeHill's question. What your proposing just can't happen. | |
| Sep 20, 2016 at 13:00 | comment | added | userLTK | @zephyr I might not have explained it well, but for this unlikely scenario to work, the axis of rotation would be at an angle. A standard tidal locking the axis of rotation is perpendicular to the plane of orbit and the rate of rotation matches the orbit. But from the planet, where the moon is tidal locked, We don't see the Moon rotate, for example, but it does. If it didn't, we'd see different sides of it. And you could theoretically add a spin to the moon where it would appear to rotate in the with the axis pointing to the planet, but the real axis would be a combination of the two. | |
| Sep 20, 2016 at 12:53 | comment | added | zephyr | I'm sorry, but unless I'm completely misunderstanding what you've said, this is completely wrong. Unfortunately its too difficult to rebut all of this in a comment. Effectively it sounds like you're saying the axis of rotation could point towards the Earth, but the tidal forces would keep the "heavy" side of the moon (and thus the axis of rotation) pointing towards us. But that requires two axes of rotation which you admit is impossible. What's more tidal locking can't occur if your axis of rotation is facing the planet/star. | |
| Sep 20, 2016 at 9:05 | comment | added | Steve Jessop | "Do that long enough and the moon would begin to spin." -- well, it would begin to spin immediately, but only at a rate 1/squillionth of the rate the train is going in the opposite direction. Where 1 squillion is the ratio of angular momentums. If it was a rocket-powered train you could build up speed, like a Catherine wheel, but then you'd be better off just gluing the rocket to the moon, not putting it on rails. | |
| Sep 20, 2016 at 8:02 | history | edited | userLTK | CC BY-SA 3.0 |
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| Sep 20, 2016 at 7:33 | history | edited | userLTK | CC BY-SA 3.0 |
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| Sep 20, 2016 at 7:22 | history | answered | userLTK | CC BY-SA 3.0 |