Observers in the UK with clear skies around 1am BST on Tuesday, 21 May can see Jupiter, the solar system’s largest planet, just 4 degrees from the waning gibbous Moon low in the south-southeast. At this time both the Moon and Jupiter fit within the same field of view of binoculars magnifying less than 10×, seen against the constellation backdrop of Ophiuchus, the Serpent Bearer. Look for first-magnitude star Antares in the adjacent constellation of Scorpius just 13 degrees to the right of Jupiter. AN graphic by Ade Ashford.Keen skywatchers in Western Europe and the British Isles will already be aware of a bright ‘star’ low in the southeast shortly after local midnight. The object is, of course, a planet – none other than the solar system’s largest, Jupiter. Any potential confusion as to its identity is resolved in the small hours of Tuesday, 21 May when the waning gibbous Moon lies nearby.
Shining conspicuously at magnitude -2.6, Jupiter is already brighter than any star visible in the nighttime sky, the planet fast approaching its closest approach to Earth for the year. Opposition to the Sun occurs on 10 June, but Jupiter and Earth are nearest two days later at a distance of 4.284 astronomical units or 641 million kilometres (398 million miles).
At 1am BST on 21 May, Jupiter lies almost 652 million kilometres from Earth and appears slightly larger than 45 arcseconds in diameter. While the gibbous Moon and Jupiter may appear close together, it is merely a line of sight effect: the solar system’s largest planet is actually 1685 times farther away than our lunar neighbour.Jupiter’s Great Red Spot transits at 12:20am on 21 May and remains on show for a further hour for observers using 7.6-cm (3-inch) and larger telescopes at magnifications of 100× and more (seeing permitting). Jupiter’s innermost Galilean moon, Io, is eclipsed by the planet’s shadow at 12:22am, hence only the other three – Europa, Ganymede and Callisto – remain on show at 1am (all times given in British Summer Time). AN graphic by Ade Ashford.
In the remaining days of October and early into November, a fascinating series of planetary peregrinations plays out low in the East before dawn twilight gets too bright. Venus, like a sprinter on the inside lane of a running track, overtakes both Jupiter in Mars in two readily observable conjunctions set against the stellar backdrop of constellations Leo and Virgo.
For lunar and planetary enthusiasts, the only naked-eye planet of the evening sky is distant and tiny Mars in the constellation of Taurus. But if you’re prepared to be an early riser, the dawn sky is where you’ll find two of the solar system’s heavyweights, Jupiter and Saturn, getting up close with the Moon on 27 and 29 March, respectively.
As darkness falls, observers in Western Europe and the British Isles fortunate to have clear skies can view a naked-eye conjunction between largest planet Jupiter and the Moon. For telescope owners, Jupiter’s Great Red Spot will be on show, while Galilean moons Io and Europa partake in a close orbital dance.
