Don’t miss Jupiter’s moons and Great Red Spot during May – Astronomy Now Online

This image of Jupiter was taken on 3April 2017 when the planet was at a distance of 414million miles (667million kilometres) from Earth. The NASA/ESA Hubble Space Telescope reveals the intricate, detailed beauty of Jupiters clouds as arranged into bands of different latitudes. Lighter coloured areas, called zones, are high-pressure where the atmosphere rises. Darker low-pressure regions where air falls are called belts. Constantly stormy weather occurs where these opposing east-to-west and west-to-east flows interact. The planets Great Red Spot (GRS, lower left), is a long-lived storm roughly the diameter of Earth. Oval BA, affectionately referred to as the Little Red Spot (lower right), transits roughly 90minutes ahead of the GRS. Image credit: NASA, ESA, and A. Simon (GSFC).Observers in the heart of the British Isles have already entered that time of the year when astronomical twilight lasts all night. But even if the sky never truly gets dark, take solace in the sight of Jupiter, currently highest in the sky to the south around 10pmBST.

The Solar Systems largest planet is now seven weeks past opposition, but still presents a magnitude-2.3 disc with an angular width of 42arcseconds. This is means that a telescope magnification of just 45 is sufficient to enlarge it to the same apparent size of an average full Moon as seen with the unaided eye.

Even the smallest telescope (and powerful binoculars, if suitably steadied) will reveal Jupiters four largest Galilean moons Io, Europa, Ganymede and Callisto in their orbital dance around their parent planet.

With a quality telescope of 3-inch (7.6-cm) aperture or greater at magnifications of 100 and more you can occasionally observe (subject to good seeing conditions) the shadows of these moons slowly drift slowly across the face of Jupiter, like ink-black dots. The timings of the start and end of such events visible from the UK for the remainder of the month are tabulated below. The times that the moons themselves are occulted (hidden) by Jupiter, or pass into or emerge from the planets shadow (eclipsed) are also shown.On the UK morning of Sunday 28May 2017, the shadows of Jupiters Galilean moons Io and Ganymede may be seen simultaneously on the face of their parent planet from 1:16am to 1:39amBST. This computer simulation depicts the scene at 1:20amBST. Note that this is an erect-image view (north up, east left). Users of Newtonian/Dobsonian telescopes should rotate this image 180degrees to match the eyepiece view, while owners of refractors, Maksutov- and Schmidt-Cassegrain telescopes with a star diagonal should mirror the image left to right. AN graphic by Ade Ashford/SkySafari.Great Red Spot and OvalBA (aka Little Red Spot) Jupiters Great Red Spot (GRS) also puts on an appearance at times suitable for observing from the UK during the remainder of the month, also shown in the table below. The GRS is said to transit when it lies on an imaginary line joining Jupiters north and south poles. Owing to the planets fast rotation (at the latitude of the Great Red Spot it takes little more than 9h55m to make one revolution), the GRS is well seen for roughly an hour either side of the transit time. The Great Red Spot has an unmistakable brick red hue at present, making it an easy object to identify in quality telescopes capable of 100 magnification or more when seeing conditions are good.

For observers with 8-inch (20-cm) and larger telescopes, try to see the smaller OvalBA (also shown in the image at the top of the page), popularly known as the Little Red Spot though do bear in mind that it transits the central meridian of Jupiter around 1hours before the times given for the GRS.Predictions for the start and end times of Galilean shadow transits, plus information on their eclipses and occultations for any given date in a slightly more user friendly format may also be obtained through our 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 phenomena events are in Universal Time (UT). For help using the Almanac, see this article.

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Don't miss Jupiter's moons and Great Red Spot during May - Astronomy Now Online