Axis Orientation and Orbit of Uranus
Date: Winter 2013-14
Reading the following on the Internet about the axial tilt of planet Uranus: One of the most distinctive features of Uranus is its axial tilt of ninety-eight degrees. Consequently, for part of its orbit, one pole faces the sun continually while the other pole faces away. At the other side of its orbit, (half of the orbit away) the orientation of the poles towards the sun is reversed.
I have tried several times to visually orbit with Uranus and its tilted axis around the sun and have not been able to see the reversal of the orientation of its poles. Every time I do one orbit, the pole that is pointing in the direction of the sun at the start,continues pointing in the direction of the sun during the entire orbit.
The orientation of Uranus alters as slowly as it orbits the Sun. Its polar axis remains pointing in the same direction throughout its orbit.
Do the following:
Hold one of your fists clenched up in the air in front of you (that is the Sun),
With your other hand, hold a small ball between your thumb and first finger, with the two contact points LEVEL (that is Uranus, and the contact points being the poles),
Keep the contact points in alignment with a point on your horizon or some semi-distant object (a tree if outside, the corner of a room if inside)
While holding "Uranus" down from the top, and the "Sun" up from the bottom (or vice versa), you can move "Uranus" around your fist (in an anti-clockwise direction) keeping the alignment with the tree or corner of the room.
From this, you can see that Uranus goes through a sequence of 'the Sun over one pole' to 'over the equator' quarter of its orbit later, 'over the other pole' at half-orbit, then over the equator again at three-quarter orbit, then back to its original position at full orbit.
I hope that this answers your question.
Try switching your reference frame. Remember that the physical laws (and the resultant observed data) are the same regardless of the chosen reference inertial frame. So - hold Uranus (with is axial tilt) in place (central reference frame) and move the Sun around it. You will quickly see that each pole points to the Sun for half the time.
To get/fix your difficulty with using the Sun as the reference frame, do the experiment as above, but carefully observe the relationship of the axial tilt direction (which is relative to the orbital plane and not to the Sun) with the Sun as the Sun moves around Uranus. You will see that the tilt direction is not constantly facing the Sun. … In effect, Uranus does not "roll" along its orbital path.
Greg (Roberto Gregorius)
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Update: December 2011