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In what direction does the Sun rotate in the geocentric model?
It seems to me that this should rotate in a clockwise direction around Earth (as seen from the north pole), but all the illustrations I've found indicate the opposite. Am I missing something? A counter-clockwise rotation of the Sun would have sunrises in the west, right?

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Sun (and everything else in the sky) participate in two motions.

  1. Sky as a whole (the sphere of fixed stars) rotates clockwise, 1 rotation per 24 hours. BTW for this reason we call this direction clockwise. Our clocks are made to model this rotation (except that the hour hand performs two rotations during the time when the sky perform one rotation).

For this reason EVERYTHING (Sun, all stars, Moon and planets) rise in the East and set in the West every day.

  1. With respect to the sphere of fixed stars, every other object, including Sun has its own motion. It is this motion that is described in illustrations. Most of these motions are counterclokwise, in particular Sun describes the a circle in the sphere of fixed stars counterclockwise, one rotation in a year.

In other words, if you observe Sun, and put in on the star globe every day at the same time, you will discover that during a year it described one full circle counterclockwise.

Remark. All this description assumes that you look from the Northern hemisphere. In Australia, all directions of rotations are opposite (for Southern hemisphere, all "clockwise" and "counterclockwise" in my answer have to be interchanged.)

Remark 2. By the way, in mathematics counterclockwise is called the "positive direction": in polar coordinates, polar angle increases counterclockwise. This is because mathematics was always closely connected with astronomy. So mathematicians used the astronomical convention, while clockmakers are more concerned with everyday needs of ordinary people.

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  • $\begingroup$ Wouldn't the Sun rise in the west if it rotates counterclockwise around a fixed Earth? $\endgroup$ Mar 2 at 13:09
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    $\begingroup$ Read carefully what I wrote. What you see, first of all is the rotation described in section 1. What they show n the pictures is MUCH SLOWER rotation described in section 2. $\endgroup$ Mar 2 at 13:11
  • $\begingroup$ If I understand you correctly the Sun's actual direction of rotation is clockwise, but because this is slower than the clockwise rotation of the stars, the Sun's path describes a counterclockwise yearly rotation. Is that correct? $\endgroup$ Mar 2 at 13:19
  • $\begingroup$ The word "actual" in your question makes no sense. I repeat: Sun participates in two rotations: one (slow) counterclockwise, another (fast) clockwise. So most people, who don't care about astronomy, notice only the fast rotation. But astronomers are more interested in the slow one. $\endgroup$ Mar 2 at 13:24
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    $\begingroup$ @Torsten Schoeneberg: Sure they do. But all "clockwise" and "counterclockwise" in my explanation have to be reversed in Australia. Daily progress of the Sun is counterclockwise there. If you use your standard wristwatch. $\endgroup$ Mar 2 at 16:13

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