Events of Jupiter's Galilean Satellites

Eclipses, occultations, transits and shadow transit of all four Galilean satellites will be occurring at regular intervals during December. A table of events visible during the month from NZ is included.

Eclipses occur when a satellite moves through the shadow of Jupiter. As it moves into the shadow the satellite will gradually fade from view and disappear. When it comes out of the shadow a faint spot of light will appear and gradually brighten.
Occultations occur when a satellite moves behind Jupiter as seen from the Earth. Hence during an occultation the satellite is hidden by the planet.
Transits occur when a satellite moves across the face of Jupiter as seen from the Earth.
Shadow transits occur when the shadow of the satellite cast by the Sun moves across the face of the planet

Occultations always start at the western limb of Jupiter and end at the east. Transits always start at the eastern limb of the planet and end at the west. In both cases the satellite will appear to "sink" into the bright limb of Jupiter at the ingress and gradually emerge from the limb of Jupiter at an egress.

In general eclipse events take place when the satellite is a small distance away from Jupiter as seen from the Earth. After opposition, as in December, eclipses take place to the west of Jupiter.

All these events can be observed through a small telescope. Note that when Jupiter is viewed through an undriven telescope its image will drift to the west. This enables the west side of the planet to be determined.

In the case of disappearances into eclipse (EcD) the satellite is likely to be visible as it fades for a minute or two after the predicted time. For reappearances (EcR) the satellite will start to emerge a minute or two before the predicted time.

The north pole of Jupiter is now tilted very slightly towards the Sun. As a result of the slight tilt all events appear to take almost in line with Jupiter's equator. From New Zealand Jupiter's north pole is the lower pole of the planet.