5.8 The JupiterSystemPlot Function
JupiterSystemPlot is useful for displaying a plot of the four Galilean moons orbiting Jupiter on a given date.
Plotting a representation of the Jovian moon system.
As seen from the Earth, the Galilean moons around Jupiter can undergo various special events every few days. Four types of events are possible. First, a moon can transit across the Jovian disk; second, a moon can cast a shadow on the Jovian disk; third, a moon can hide (or be occluded) behind the Jovian disk; and fourth, a moon can be eclipsed in the shadow of the Jovian disk.
All of these special events are indicated in the JupiterSystemPlot graphic for a given date and time.
The moons Io and Ganymede both fall in the "Shadow" colored region in this graphic, which means their shadows are cast onto the Jovian disk. Similarly, Io falls in the "Transit" region, which means it is in front of the Jovian disk as seen from the Earth. You can confirm this with a call to PlanetPlot3D.
As expected, Ganymede's shadow is ingressing on the left or eastern edge, and Io's shadow is egressing on the right or western edge. The green dot is Io itself, which is making a transit.