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Name: Shawn
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A


Question:
Hello, I had a student ask me this question, and I could not give him a direct answer, Please help! It is of course stated that the earth rotates on the same horizontal plane around the sun, while spinning on its 23.5 degree axis. My question is simple; what kind of proof exists that could disprove the earth (along with the rest of the planets) are actually rotating around the sun at the 23.5 degree angle, not following the horizontal plane, and the earth possibly spinning perfectly vertically on its axis instead. This would cause the exact same seasonal changes, and seems to physically make more sense to me. Looking for solid proof, which I believe may present it self by the view of the sun.


Replies:
Shawn,

I am not sure I understand your question. You are asking for any evidence that would *disprove* that the Earth is -as it is known to be- precessing through a 23 degree angle?

If the Earth were rotating about an axis that were exactly perpendicular to the plane of revolution around the Sun then:
a) the northern and southern hemispheres would be exposed to the same amount of sunlight -since they would present exactly the same degree to the Sun- and therefore there would be no seasonal difference between latitudes that are equidistant from the equator;
b) if the Earth does not precess (move back and forth between a +23 to a -23 axis to the plane of revolution) then there would be no seasons since throughout the year the angle of exposure to the Sun would be the same;
c) if the Earth does not precess, then weather conditions could be milder because there would be less fluctuations and thermal zones since the Earth would be heated "evenly" . . .

Since we do not see such situations, we must conclude that there is in fact a +/- 23 degree precession.

I hope I have addressed your question.

Greg (Roberto Gregorius)
Canisius College


I do not really follow the distinction you are making in your question. In both cases the axis of the Earth's orbital plane of revolution around the Sun and the axis of its rotation are inclined at a 23.5 degree angle. Are you asking which axis is properly considered "vertical"? If so, the answer is that either or neither are fine. What preferred direction counts as "vertical"? The orbit of the Earth? The rotation of the Earth? The plane of the galaxy? The direction that appears "up" to you at any given time?

One thing to bear in mind also when deciding on a preferred reference direction is that the Earth's axis of daily rotation changes over time; it is precessing due to gravitational influences of the other objects in the solar system on its slightly out-of-round shape.

Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming



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