Equant Machine

Full-screen version
Here, you can play with the equant model used by the “ancients” before Kepler. Everything is adjustable here:

What am I seeing?

On the left, you are seeing the actual model of planetary motion. The line from the equant moves at a uniform speed (press e to see only the equant line), moving the black planet around the orbit. The center of vision is watching it, with a red line drawn to indicate the line of sight.

On the right are the extended lines of vision. The blue line indicates where the equant sees the planet, while the red line indicates where the center of vision sees the planets. The blue line on the right is parallel to the blue line on the left, and likewise for the red lines. This allows you to watch the perceived speeding-up and slowing-down of the planet.