

VenusPhases
General Description
This program illustrates the phases of Venus as predicted by either the Copernican system of the Ptolemaic system (the Copernican system is the default). One window shows Earth, the sun, and Venus on its Copernican orbit. Venus is shown as a disk with the side facing the sun colored yellow (since it reflects the sun's light) and the other side colored dark gray (since that side is dark). Playing the simulation puts all moving objects (ie Venus and Earth/Sun) in motion. Another window shows what Venus would look at this position, when viewed from Earth through a telescope. A menu option displays another window showing Galileo's drawings of his telescope observations of Venus.
All orbits are drawn to scale. However, the size of the planets/Sun are greatly exaggerated (they should all be essentially point-like on the scale shown) and even the relative sizes are not correct (Earth and Venus are MUCH smaller than Sun).
Orbit Frame
- Select System Menu:
- Copernican: in this system Venus orbits Sun and is closer to Sun than Earth is.
- Ptolemaic: in this system Venus orbits in a circle whose center always lies between Earth and Sun, with Sun lying entirely outside of Venus' orbit.
- General Options Menu
- Show Telescope View of Venus: show the Telescope View Frame (see below).
- Show Light Band: show band of light connecting Earth and Venus. This band shows the portion of Venus visible from Earth and the portion of Earth from which Venus is visible (assumes Venus can be viewed during daylight).
- Show Galileo's Drawings of Venus: displays a window showing the sketches Galileo made while observing Venus through his telescope. These sketches can be compared to what is seen in the Telescope View frame to determine whether they agree more with the Copernican or Ptolemaic system.
- Copernican Options Menu
- Show Orbit of Venus: show circle representing Venus' Copernican orbit.
- Show Earth's Orbit: show circle representing the orbit of Earth.
- Ptolemaic Options Menu
- Show Deferent of Venus: show circle representing the Ptolemaic deferent of Venus.
- Show Epicycle of Venus: show circle representing the Ptolemaic epicycle of Venus.
- Show Sun's Orbit: show circle representing the orbit of Sun.
- Visual Elements
- Blue/gray disk: Earth.
- Yellow/gray disk: Venus.
- Yellow circle: Copernican orbit of Venus.
- Blue circle: Copernican orbit of Earth.
- Orange circle: Ptolemaic orbit of Sun.
- Green circle: Ptolemaic deferent of Venus.
- Magenta circle: Ptolemaic epicycle of Venus.
- Orange disk: the sun.
- Transparent white band: a band of light showing the portion of Venus visible from Earth and the portion of Earth from which Venus is visible (assumes Venus can be viewed during daylight).
- Controls
- Play/Pause button: play or pause the simulation. When the simulation is playing all moving objects (ie Venus and Earth/Sun) will move.
- Step button: advance the simulaton by one time step.
- Reset angles button: resets all angles to zero.
- Reset button: reset the simulation to its initial state.
- Slider: controls the location of Venus along its orbit (or Ptolemaic epicycle). Moving the slider will cause only Venus to move, so this can be used to focus on the relative motion of Venus.
Telescope View Frame
Shows the view of Venus as seen from Earth when the Venus is in the position shown in the Orbit Frame. The phases of Venus are not apparent to the naked eye, but this view shows what we would see through a telescope if Copernicus' theory were correct.
Galileo's Drawings of Venus
Shows the sketches Galileo made while observing Venus through his telescope. These sketches can be compared to the output in the Telescope View Frame to determine whether or not Galileo's observation support the Copernican or Ptolemaic system.
Todd K. Timberlake (ttimberlake@berry.edu)