In 2009, Jupiter is reasonably well-placed for telescopic observing from May through November at mid-northern latitudes, and from April through December in the Southern Hemisphere. At the beginning of this period, Jupiter is visible only around dawn, but by August the king of planets is fairly high in the sky by midnight or earlier.

Virtually any telescope will show Jupiter's four Galilean moons and their interesting interactions with the planet or its shadow. During the course of every revolution, Io, Europa, and Ganymede pass in front of and then behind Jupiter’s disk. Wide-ranging Callisto missed the planet’s disk, as seen from Earth, between late October 2004 and December 2007, but this moon's encounters have now resumed.

For the convenience of telescopic observers, we are making available a complete list of Jupiter's satellite phenomena for 2009 to supplement the monthly lists that usually (but not always) appear in Sky & Telescope. The list is in the form of a 24-page PDF, so you'll need a free copy of Adobe Reader software to open it and print it.

Phenomena of Jupiter's Moons, 2009 (148-KB PDF)

For a graphic overview of the moons' motions, download one of our printable single-page PDFs. Click below for the desired month.

April 2009
May 2009
June 2009
July 2009
August 2009
September 2009
October 2009
November 2009
December 2009

You can also run our Javascript utility to view the positions of Jupiter's moons at any moment.

In 2009, the orbits of Jupiter’s moons almost perfectly edge-on to the Sun and to the Earth. As a result, the moons eclipse and occult one another. These “mutual phenomena” are fascinating to watch, and digital imaging technology now allows observers to image them and time them as never before. Predictions of all these events are given in the online Astronomical Almanac.

Jupiter's famous Great Red Spot (GRS) is much harder to spot than the Galilean moons. Although it's quite large, the low contrast of the GRS can make it hard to see unless Jupiter is quite high above the horizon and the astronomical seeing is quite good. In addition, you need a reasonably big telescope (preferably at least 6 inches of aperture) with good optical quality.

But most important of all, you can only see the GRS when it's on the side of Jupiter that's facing Earth. And it's only reasonably easy to see within about an hour of the time that it transits, passing halfway across Jupiter's disk during each 9-hour and 55-minute rotation.

You can use our Javascript utility to find predicted times of GRS transits, or cllick here for a printable table of all predicted GRS transits in 2009.