Description

This simulation illustrates the motion of the Moons of Jupiter relative to Jupiter as seen from Earth. The simulation shows a view through a telescope with Jupiter always centered in the view. The four Galilean moons (Io, Europa, Ganymede, and Callisto) appear as small white spots that move back and forth. When the moons pass behind Jupiter they are hidden (occulted) and when they pass in front of Jupiter they cast shadows onto Jupiter (although the shadow positioning is not entirely realistic and the simulation does not depict Jovian lunar eclipses). The moons are assumed to orbit Jupiter in a common plane (which is apprxoimately correct since the all four orbits are inclined by less than half a degree to Jupiter's equatorial plane).

Controls allow the user to step forward or backward in time using a choice of four different time steps (4, 8, 24, or 48 hours). The total elapsed time is displayed. The user can also choose with width of the telescope view (6, 12, 18, or 24 arcminutes). In addition, a measuring tool can be enabled that allows the user to measure distances from the center of Jupiter (in units of Jupiter Diameters). Using this tool users can make measurements to determine the period and radius of each moon's orbit (note that Jupiter has an equatorial diameter of 0.0009558 AU). Using the results one can show that Jupiter's moons obey Kepler's third law of planetary motion, and the proportionality constant can be used to find the mass of Jupiter in solar masses.

Finally, the user can choose whether or not to label the moons (I, E, G, and C) and whether or not to include the effects of weather which will prevent observation during occasional cloudy times.

Image credits: photo of Jupiter by the Hubble Space Telescope (credit NASA/ESA/Goddard Space Flight Center), photo of the moon with clouds (from pxfuel.com).