Description

This simulation shows the predicted phases of the planets as seen from Earth, according to either the Copernican or Ptolemaic planetary system. The simulation assumes a simplified Copernican model with sun-centered circular orbits, or a simplified Ptolemaic model with earth-centered deferents. The main view shows the planetary orbit with the Sun shown in orange, the Earth in blue, and the planet in yellow (for inferior planets) or red (for superior planets). The side of earth and the planet facing the Sun is lit while the opposite side is dark (shown as dark gray). A "light band" highlights the portion of Earth from which the planet is visible and the portion of the planet that is visible from Earth. Note that the size of the planet, Earth, and Sun are greatly exaggeratted to show detail (otherwise they would all be invisiblly small on this scale).

Controls let the user play or pause the simulation, reset time to zero, reset the entire simulation, or adjust the speed of the simulation. The user can select whether or not the show the Ptolemaic (rather than Copernican) model, to display the light band, to show the telescopic view of the planet, to show Galileo's sketches of his telescopic observations of the planets (for comparison to the predictions from the model), and which planet to view. The telescopic view shows the changing appearance of the planet as seen through a telescope on Earth. Note that the magnification is set so that the planet will nearly fill the view when it is at maximum apparent size (this magnification is different for different planets/systems). Galileo's sketches show Saturn (top left), Jupiter (top center), Mars (top right), and several views of Venus (bottom row).