The giant planet Jupiter, brighter than any star, stands 30° to 35° high in the S during Britain’s evening twilight at present and tracks westwards to dip beneath our W horizon about one hour before dawn.
Stable binoculars reveal its four main moons while telescopes show its disc, 42 arcsec wide and crossed by bands of cloud aligned parallel to its equator. Whorls, streaks and spots, including the Great Red Spot, are also seen, all carried across the disc as the planet rotates in a little under 10 hours.
Jupiter is currently tracking westwards in Virgo, 11° NW (above-right) of the star Spica. That motion reverses on 10 June following a stationary point 3° SE of the celebrated double star Porrima whose two equal stars of mag 3.5 currently lie less than 3 arcsec apart as they orbit each other every 169 years.
A much easier naked-eye double star lies almost directly overhead as Jupiter crosses the meridian and is identified on our chart which look northwards from Virgo to the zenith and beyond as the night begins at present. Mizar shines at mag 2.2 in the handle of the Plough, perhaps better known as the Big Dipper by US starwatchers, and has a mag 4.0 companion, Alcor, which is 12 arcmin (about a third of a Moon-width) away. Together they are dubbed the Horse and Rider, but whether they are tied together by gravity is open to question.
A curving line along the Plough’s handle extends to the red giant Arcturus in Bootes, the fourth-brightest star in the night sky, the second brightest ever seen from Britain (after Sirius) and the brightest in the sky’s N hemisphere. There is a mnemonic that goes “arc to Arcturus, spike to Spica” since our curving line may be stretched further to reach Spica. I suggest that this year we could recast this to read “arc to Arcturus, jump to Jupiter”, although the planet can hardly be mistaken.
The region of sky to the N of Jupiter has been called the Realm of the Galaxies. Halfway between the stars Vindemiatrix in Virgo and Denebola in Leo, and at a distance of some 54m light years, lies the heart of the Virgo cluster of galaxies. Its brightest galaxies were spotted late in the 18th century and found their way into Messier’s iconic catalogue of fuzzy celestial objects. Now we suspect that it holds in excess of 1,300 galaxies, all telescopic objects.
On a still larger scale, the Virgo cluster is just one element of the Virgo supercluster of galaxies which spills over the entire area of our chart and even includes the Local Group cluster of galaxies to which our Milky Way belongs. Another supercluster, centred in the constellation of Coma Berenices (COMA on our chart), lies some 15° further N and almost twice as far away.
The only one of the 88 constellations to be named after a real person, Queen Berenice II of Egypt, Coma contains no bright stars but is distinguished by an inverted V of dim stars – actually a real star cluster called Melotte 111 at a distance of 280 light years. It is said to represent the Queen’s tresses, which she sacrificed as a votive offering.