A Jupiter Almanac

Jupiter spends its 2016-2017 apparition in Virgo. At the end of 2016, Jupiter joins us in the morning, rising progressively earlier in the hours between midnight and dawn. As winter progresses, Jupiter transitions to an all-night object, rising about two hours before midnight in February and staying with us until sunrise. By the June solstice, Jupiter is visible at sunset and sets near midnight. By mid-August, Jupiter is an evening visitor, setting before midnight. In December 2017, Jupiter will be an early morning riser once again.

Jupiter with Moons
Jupiter with three of its Galilean satellites: Io, Europa, and Callistor (left to right), recorded on March 16, 2003.
Virtually any telescope will show Jupiter's four Galilean moons and their interesting interactions with the planet or its shadow. For the convenience of telescopic observers, we are making available a list of Jupiter's satellite phenomena through December 2018 to supplement the monthly lists that usually (but not always) appear in Sky & Telescope.

Phenomena of Jupiter's Moons in 2017
Phenomena of Jupiter's Moons in 2018

You can also run our Jupiter's Moons observing tool to view the positions of the four Galilean moons at any moment.

Mutual Phenomena of Jupiter's Moons

About every six years the Earth’s orbit crosses the orbital planes of the four Galilean satellites. The last best chance to see the effects of this alignment was in late 2014 and most of 2015, when the orbits of Jupiter’s moons were almost perfectly edge-on to the Sun and Earth. The next best chance to see the moons eclipse and occult one another will be in 2021. 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.

Spotting the Great Red Spot

The Great Red Spot can only be seen when it's near the center of Jupiter's rapidly rotating disk.
S&T: Sean Walker
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 the planet 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 Great Red Spot Calculator to find predicted times of GRS transits.

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