The Planet Uranus' Tilt

Uranus is tilted so that the axis of its poles are in the plane of the other planets of the solar system instead of more or less almost perpendicular to it. The question is, is it titled so that, say, one of its poles is pointing toward the sun or is it pointing along at some angle to that. And 2) which one is the north pole of Uranus and which is the south pole?

Uranus is tilted 97.9[sup]o[/sup] from the vertical. It’s magnetic axis, however, is actually much closer to being vertical; it’s offset 60[sup]o[/sup] from the axis of rotation. The megnetic north pole is the one at the “top” of the planet, and the rotational north pole is the one tilted slightly “upward” (obviously there is no “up” or “down” in space, but we have agreed on certain conventions for the solar system, i.e. north poles face up and south poles face down).

One of the poles will face the sun at a certain point in Uranus’s revolution around the sun, but as it revolves that pole will move away, and at the opposite side of the sun the opposite pole will face it. A very severe day-night cycle, that.

I hope I answered your questions.


Actually, scratch that. Uranus’s rotational north pole, strangely enough, is actually the one slightly tilted “downwards.”


So Uranus, is orbiting around the sun not like a top, but like a bowling ball?

You were right the first time. The IAU has decreed that the north pole of all planets, stars, galaxies, etc. is the one the points to the north ecliptic hemisphere. This means the axial tilt of Uranus is officially 82.1 degrees retrograde.

That said, mathematically, it’s usually easier to treat the north pole as the one the object rotates counterclockwise around. This is also the more intuitive definition for many people.

Sometimes. That is, sometimes its rotation looks like it is rolling the planet in the direction of its orbit. Half a Uranian year later, the rotation is completely opposite of that. And a quarter U-year before and after that, the rotation looks like it should roll the planet either toward or away from the sun.

This is because Uranus’s axis is pointed toward the same place in the heavens, like Earth’s is pointed at the North Star. (I know, the E-axis is wobbling to different points. But the time scale that this happens is too slow for humans to notice.) This tilt in all planets’ rotational axes is what causes seasons (if they have the atmosphere to make it noticable).

So just to clarify, which has that organization decreed is the north pole, the one Uranus rotates counterclockwise about, or the one it rotates clockwise around? And if the former, is that the one that tilts a little downward or a little upward?
As the old poem goes,
There once was a man from Uranus
Who came down to earth to be famous;
“On Uranus,” he said,
“All ambition is dead,
And conditions are generally heinous.”

The man from Uranus, named Fred
Looked like us, were we pale, bald, and dead.
But we got him some suits
And a good pair of boots
And plopped a red wig on his head.

Fred soon hired a hall for his speech:
“Be my guest, Give it a rest,
Up is east, down is west,
And don’t let your grasp be exceeded by your reach.”
(it goes on, and you can see why I need to know where east and west is in order to make sure my poem is correct).
copyright by D.Willard

Why is Uranus like that?

I think the best guess is that Uranus, sometime in its career, got slammed pretty hard by a wayward comet or astroid, knocking it on its side.


For those of you who like photos to go with your platitudes and plongitudes, here’s the latest reconstructed image, courtesy of Japan’s Subaru (Pleiades) telescope and BBC:

Here’s a bigger version:

That picture referred to above doesn’t seem to have the two satellites of Uranus in the same plane. This reminds me that Uranus is like a target with the planet in the middle and the orbits of the satellites and the rings around it and they are all in the plane of Uranus’s equator. In other words if we flew to Uranus in a rocket ship we would see this like target effect. In other words when the planet was tilted, all its satellites and rings tilted right along with it instead of staying in the plane of the solar system, which the usually are in. One whonders why this happen?

Actually, it’s much more common for satellites and rings to orbit in the plane of their primary’s equator. Our Moon, which is more or less in the ecliptic, is an exception, which is one of the arguments for considering it a planet in its own right.

I’m not sure why the primary’s equatorial plane would be preferred, but I suspect it may have something to do with tidal forces. Do any of the other board astronomers know?

Can anything be inferred about the age of Uranus’ satellites as such from thier orbits? That is, if they were there before Uranus got slammed (or whatever) would they have made the shift with the planet (if so, their orbits must have been pretty weird for a while…)? Or might it indicate that they are late additions?
(I was an astro major once upon a time…)

But I thought the moon’s orbit was in the same plane as the earth’s orbit around the sun.
Or just a few degrees off actually. What is this ecliptic? Also, since the moons and rings of Uranus are not in the plane of the planet’s orbit around the sun, I feel that they eventually will be. They will fall down (and up) to that plane some day. Unless it is the swishing along of the planet’s equator that is exerting a force on them and keeping them there. I also think that the planet itself will right itself and someday its equator will move to the normal position. Indeed, the slight tilt of the earth away from a vertical to its orbit around the sun will someday go away and the earth will right itself too. All will be perfection. The only reason things are off is that they just haven’t had time to settle down.
All is temporary, though and in process, and maybe the sun will flare out and end it all before all this righting takes place.

You’ve got it. The plane of the Earth’s (and other planets’) orbit around the sun is called the ecliptic. As for your notion that the planets will all eventually right themselves, there’s no evidence that this is occuring, and no known mechanism by which it would occur. The direction of the Earth’s spin is changing, but the angle between “terrestrial north” and “solar north” is a constant.