Magnitude +2.9 star Mu (μ) Geminorum, better nown as Tejat in the constellation of Gemini, is occulted (hidden) by the rising 13-day-old waxing gibbous Moon early on the evening of Thursday, 9 January 2020 as seen from the British Isles. This graphic shows the event’s progress as seen from London and Edinburgh, clearly demonstrating the effect of geographical latitude. AN graphic by Ade Ashford.If the early evening sky of Thursday, 9 January is clear, observers in the British Isles get the opportunity to witness a conspicuous naked-eye star slip behind the rising waxing gibbous Moon. Magnitude +2.9 Mu (μ) Geminorum, with the proper name Tejat, lies near the western edge of the constellation Gemini. The precise time and duration of the star’s disappearance behind the Moon – an event known as a lunar occultation, from the Latin occulo, ‘to hide’ – depends on where you live in the UK.
Observers in London will see, weather permitting, Tejat disappear at the darkened limb (edge) of the 13-day-old Moon shortly after 5:05pm GMT (17:05 UT) and reappear at the bright lunar limb 45 minutes later. For a skywatcher in Edinburgh, the star’s corresponding disappearance and reappearance times are a few seconds before 5:17pm GMT (17:17 UT) and 5:52pm GMT, respectively.
Mid-occultation of Tejat takes place with the Moon some 15 degrees (about a span-and-a-half of a fist held at arm’s length) above the UK’s east-northeast horizon. While it is an easy spectacle to follow in a small telescope, the star’s reappearance at the bright lunar limb might be a challenge for binocular users. As with all occultation observations, it pays to be setup and scrutinising the Moon 10 minutes before the predicted times, particularly if you live some distance from either London or Edinburgh.
In the dawn twilight of Saturday, 5 September, observers in the British Isles with clear skies can see the last quarter Moon pass in front of first-magnitude star Aldebaran in the constellation Taurus — the brightest star (aside from the Sun) to be occulted by the Moon as seen from the UK this year.
In this image from NASA’s Cassini probe, Saturn’s moon Rhea appears dazzlingly bright in full sunlight. This is the signature of the water ice that forms most of the moon’s surface.
Mars may be almost four weeks past opposition, but it’s still an imposing sight low in the southern sky around local midnight. But if you are in any doubt about identifying the Red Planet, the waxing gibbous Moon acts as a convenient celestial guide late into the UK night of Thursday, 23 August. See both the Moon and the Red Planet in the same field of view of low-power binoculars.
