Turn off the daylight and horizon displays. Use the
"Planet" Palette to center on Jupiter and lock on Jupiter.
Use the "Settings" button to set Orientation to Equatorial.
Use the "Zoom" button to zoom in until the field of view
is 20º of arc. Set the time step to 1 hour. Step ahead in time
until Io just starts to cross the disk of Jupiter. Record the
time and date. Continue to step ahead until Io completes
an entire orbit and begins to cross the disk of Jupiter again.
Record the time and date and calculate the orbital period
of Io. Continue to step ahead until Io and Jupiter are as
widely separated as they get during an Io orbit. Use the
Angular Separation Tool to find the angular radius of Io's
orbit. Point at Jupiter using the Selection Tool and record
Jupiter's (and Io's) distance from the Earth. Use the small
angle equation to find the radius of Io's orbit in km. Use
Newton's version of Kepler's third law (Equation 5.4) to
find the mass of Jupiter.
