Axial tilt of Uranus?

[Josh Wilson]

The axial tilt of Uranus, according to Wikipedia, is 97.77 degrees. This means, if you think about it, that Uranus is pointing down. So shouldn't the axial tilt be 82.23 degrees? I guess it really matters on which pole of Uranus you consider to be pointed up...

[George Jones]

The axial tilt of Uranus, according to Wikipedia, is 97.77 degrees. This means, if you think about it, that Uranus is pointing down. So shouldn't the axial tilt be 82.23 degrees? I guess it really matters on which pole of Uranus you consider to be pointed up...

Let's consider a hypothetical Uranus. Looking down on the plane of the orbit for this hypothetical Uranus, we see that it orbits the Sun in a counterclockwise direction. Suppose the spin axis is perpendicular to the orbital plane, and that it spins in the same sense that it orbits, counterclockwise. To change hypothetical Uranus to real Uranus, we have to tilt its spin axis by 97.8 degree, i.e., because the tilt is greater than 90, Uranus spins (slightly) in the opposite sense to which it orbits.

[Earl]

if I understand this right, one pole is pointed (more or less) at the sun all the time the other is in darkness all the time?

[Earl]

im a little confused now: from Wikipedia

Uranus has an axial tilt of 97.77 degrees, so its axis of rotation is approximately parallel with the plane of the Solar System. This gives it seasonal changes completely unlike those of the other major planets. Other planets can be visualized to rotate like tilted spinning tops on the plane of the Solar System, while Uranus rotates more like a tilted rolling ball. Near the time of Uranian solstices, one pole faces the Sun continuously while the other pole faces away. Only a narrow strip around the equator experiences a rapid day-night cycle, but with the Sun very low over the horizon as in the Earth's polar regions. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.^[47] Near the time of the equinoxes, the Sun faces the equator of Uranus giving a period of day-night cycles similar to those seen on most of the other planets. Uranus reached its most recent equinox on December 7, 2007.^[48][49]

I cant visualize this.

[Treeden]

This might help...

[Earl]

This might help...

Perfect thanks

[sologuitarist61]

This might help...

A picture paints a thousand words ...

[Josh Wilson]

Very helpful image, treeden. Which way is north in that picture?

[J_M_Franklin]

I believe that based on what is currently known, in the pictures above the pole marked A is actually the Uranian North Pole and in case anyone is wondering about seasons on the planet.

Unlike Jupiter and Saturn, the clouds on Uranus appear relatively featureless. One primary reason for this is due to the planet's tilt. On Earth, the northern and southern mid-latitudes have seasons because our planet's rotational axis is tilted 23° with respect to the plane of its orbit. Uranus is an extreme case. As has been mentioned, the rotational axis is tilted almost 98° in respect of it's orbital plane, therefore, as Uranus orbits the Sun, the Sun shines directly down on the north pole, then the northern latitudes, the equator, the southern hemisphere, the south pole, and so on. In the 1990s, the Sun was shining down on the southern mid-latitudes. In 2007, the Sun shone directly over Uranus's equator. As the Sun is the primary driving force for all planetary weather, Uranus is a strange place with 21yr seasons. For a quarter of the Uranian year (one Uranian year is 84 Earth years), the Sun shines over each pole, leaving the opposite side of the planet in frigid darkness.

[Treeden]

Perfect thanks

You're welcome Earl, it made it easier for me to understand too.

A picture paints a thousand words ...

Just as well in my case, or I'd be lost!

Very helpful image, treeden. Which way is north in that picture?

Well, if you adopt the 'right hand rule' and if that drawing is accurate with regard to the direction of rotation, then the north pole should in fact be B.

From wikipedia:

"Orientation of the axes is established by the right hand rule for both the rotation and the orbital motion. When the fingers of the right hand curl around in the direction of the object's rotation, the thumb points in the direction of its north pole"

I believe that based on what is currently known, in the pictures above the pole marked A is actually the Uranian North Pole...

I'm not saying you're wrong J_M, my conclusion is based on the accuracy of the drawing I posted earlier, taken from here, and may well be wrong?

Rob