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The blue dot at the center is the Earth, and the point closest to it is the equant.

The center of the deferent, which is the big green circle, itself moves on the small green circle.

The pink dot on the epicycle is Mercury.

The outermost circle represents the celestial sphere, which carries the mean Sun and the projection of Mercury.

Tap on the canvas (or press Space) to start/stop the animation.

Use the sliders (or ASZX buttons) to adjust the speed and the trail length.