Observers in the UK with a clear sky high to the south-southeast shortly after midnight on Sunday, 12 January 2020 can see the 16-day-old waning gibbous Moon just three-quarters of a degree north of the beautiful open star cluster Messier 44, otherwise known as Praesepe, or the Beehive Cluster. AN graphic by Ade Ashford.If you own a pair of binoculars or a small telescope, you may wish to take a look at the Moon on the night of 11–12 January 2020 since it lies in the constellation of Cancer, the Crab. If you look a little more closely, you’ll see that the Moon lies in the same field of view as the glorious open star cluster known as Praesepe, the Beehive Cluster, or more prosaically as Messier 44.
For observers in the British Isles, the Moon’s orbital motion doesn’t bring it closest to the Beehive Cluster until the calendar clicks onto 12 January, by which time the pair are high in the south-southeast. At their closest – 12:30am GMT (00:30 UT) – the 16-day-old waning gibbous Moon lies just three-quarters of a degree north of the heart of Praesepe. In a telescope, use your lowest magnification eyepiece and watch as the Moon glides over the northern edge of M44, occulting (passing in front of) a number of its fainter stars.
A scholarly investigation of the Cairo Calendar papyrus (1244–1163 B.C.) has led researchers at the University of Helsinki to conclude that the ancient Egyptians were aware that the variable star Algol (beta Persei) had a 2.85-day period. Given that the star’s current period is 2.8673 days, this supports the theory that mass transfer between the stars of this eclipsing binary has caused a long-term increase of its orbital period.
The orbits of Jupiter’s large Galilean moons Io, Europa, Ganymede and Callisto are presently almost edge-on to our line of sight, causing the moons to regularly eclipse and occult each other. Multiple shadow transits are also on view!
Mercury is generally something of a challenge to observe, but the run-up to a particularly favourable easterly elongation occurring on 30 July provides ample opportunities for locating the innermost planet in the evening sky — particularly from the Southern Hemisphere, where a prominent celestial marker in the form of a 2-day-old Moon passes close by on 25 July.
