As I explained in detail in a former post, Jupiter was at opposition on 9 May. As June begins, the solar system’s largest planet is still prime time, unmissable as a magnitude -2.5 interloper amid the stars of Libra and found highest in the southern sky at 11pm BST for observers in the British Isles. If you’re unsure which ‘star’ is Jupiter, the 10-day-old waxing gibbous Moon lies close by at dusk on 23 June.
Jupiter’s angular size shrinks slightly from 44 to 41.4 arcseconds over the course of June as the distance between our two planets grows, but a telescope magnifying just 50× is sufficient to enlarge it to the same size as an average full Moon appears to the unaided eye. In order to see most of the following events, you’ll need powers of 100× or more and preferably a telescope of 10-cm (4-inch) aperture or larger. (See this article for a guide to observing Jupiter and its moons.)
The orbital motion of Jupiter’s bright Galilean moons Io, Europa, Ganymede and Callisto cause them to alternately pass in front of (transit) Jupiter, be hidden (occulted) by their parent planet or its shadow (eclipsed). Owing to the slight inclination of their orbits to our line of sight, outermost moon Callisto currently passes north or south of Jupiter’s disc, hence it is temporarily excluded from transits, shadow transits, occultations and eclipses.While the transit of a Galilean moon across the face of Jupiter can be challenging to view, their shadows are much easier to see in modest (4-inch, or 10-cm aperture) telescopes of good quality at magnifications of 100x or more, seen as inky black dots slowly drifting across the face of the planet.
The table below lists all Great Red Spot transits (when the giant anticyclonic storm feature crosses an imaginary line joining Jupiter’s north and south poles), Galilean moon and shadow transits, occultations and eclipses visible from the British Isles throughout the month of June. Note that the Great Red Spot is well shown for up to an hour either side of the predicted transit time.Predictions of Jovian phenomena for any given date may also be obtained through our interactive online Almanac. To see the satellite events for any given day, ensure that the ‘Add phenomena of Jupiter?’ checkbox is ticked. Like the Great Red Spot predictions, all Galilean moon events are in Universal Time (UT). For help using the Almanac, see this article.