Description

This simulation illustrates Kepler's species motrix theory from the Astronomia Nova. Kepler speculated that an immatrial force, or species, emanating from the Sun swept the planets along in their orbits. This force was stronger closer to the Sun and weaker farther away. As a result the planet wold move faster when closer to the Sun and slower when farther away. (Note: Kepler was working with a pre-Newtonian conception of motion, based largely on Aristotle's ideas about "violent motion.") The simulation shows lines, representing the species, radiating outward from the Sun. Where the lines are closer together, the species is stronger. The Earth orbits the Sun in an eccentric circular orbit, speeding up or slowing down in response to changes in the strength of the species.

Controls allow the user to speed up the simulation or change the eccentricity of Earth's orbit. Plots show the Earth's speed and distance from the Sun as a function of time.