Make the most of your Jupiter observations during May

By Ade Ashford

9 May 2016 Ade Ashford

On the night of 23—24 May, clear UK skies will permit you to observe the shadow of Callisto, Jupiter's outermost Galilean moon, crossing the northern polar regions of the planet. The event lasts from 10:22pm BST on Monday, 23 May until 12:34am BST the following morning. Phenomena of Jovian moons Io, Europa and Ganymede are also listed in the article below in addition to the planet's Great Red Spot. AN graphic by Ade Ashford.
On the night of 23—24 May, clear UK skies will permit you to observe the shadow of Callisto, Jupiter’s outermost Galilean moon, crossing the northern polar regions of the planet. The event lasts from 10:22pm BST on Monday, 23 May until 12:34am BST the following morning. Phenomena of Jovian moons Io, Europa and Ganymede are also listed in the article below in addition to the planet’s Great Red Spot. AN graphic by Ade Ashford.
Now more than two months after opposition, planet Jupiter is highest in the sky to the south before the Sun sets. By the time nautical twilight fades (~11pm BST for the centre of the British Isles), the largest planet is already descending in the southwest, but at magnitude -2.2 it is still the brightest object in the evening sky other than the Moon. (Mars, now visible very low in the southeast around 10:30pm BST, is currently magnitude -1.7.)

Galilean moon events for Io, Europa, Ganymede and Callisto

All dates and times in BST.
All dates and times in BST.

Great Red Spot (GRS)
This anticyclonic storm found just south of the planet’s South Equatorial Belt (SEB) has been observed for around four centuries. Although it is presently somewhat smaller than in recent years, the GRS presently makes up for that by taking on a distinctly reddish hue, making it easier to see in 3-inch (7.6cm) aperture telescopes, or larger.

The Great Red Spot is easiest to see when it crosses the imaginary line joining Jupiter’s north and south poles that passes through the centre of the planet’s disc. At such times we say that the GRS is ‘in transit’. For observers in the British Isles, conveniently observable transits of the Great Red Spot occur during May on the following dates and BST times: 10 (2:22am & 10:14pm), 12 (11:53pm), 15 (1:31am), 17 (11:01pm), 20 (12:40am), 22 (10:10pm), 24 (11:49pm), 29 (10:58pm).

You can obtain GRS predictions for yourself, in addition to phenomena of the Galilean moons Io, Europa, Ganymede and Callisto, for any given date or location in the world through our interactive online Almanac.

Note that the Almanac’s predictions of Jovian phenomena use 24-hour Universal Time (UT) — a global time reference based on the rotation of the Earth loosely synonymous with Greenwich Mean Time (GMT) that is one hour behind British Summer Time (BST) currently in force.

Always ensure that the Almanac’s Daylight Savings Time check-box is ticked if applicable to your date, time and location. For help using the Almanac, see this article.

Inside the magazine

Find out all you need to know about observing Jupiter and the other solar system bodies currently in the night sky in the May 2016 edition of Astronomy Now.

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The start of July finds magnitude -2.3 Jupiter almost two months past opposition and highest in the southern sky around 30 minutes before sunset for observers in the British Isles. The solar system’s largest planet may be past its best, but there still plenty of Jovian events visible from the UK.