This application simulates the apparent retrograde movement that the planets perform at certain times of the year, considering, naturally, the point of view of observation from Earth.

It is possible to simulate apparent retrograde movement using two models: Ptolemy's heliocentric and geocentric, both greatly simplified.

Buttons:

• Starts or pauses the simulation.
• Restarts the simulation.
• Configures system parameters and changes the model from heliocentrism to geocentrism and vice versa.

In the heliocentric model:

• The orbits are being considered as circular.

In the geocentric model:

• We are considering Ptolemy's old model, now outdated.
• The epicycle is being considered circular.
• We are not taking the equant into account.

In both models, the relative angular velocities of the planets are calculated from Kepler's third law.

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