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.
The last lunar occultation of a conspicuous naked-eye star for UK observers in 2014 occurs around 6 am on Tuesday, 9th December. Set your alarm and prepare your telescope for the disappearance and reapparance of λ Geminorum.
A pretty rare observational event visible across the whole of the UK, a planet occulted by the Moon, occurs on the early-evening of 5 December when the Moon moves over Uranus.
For three evenings from 26–28 February 2020, observers in Western Europe including the British Isles can watch the waxing crescent Moon’s changing configuration with brightest planet Venus in the west-southwest at dusk. The pair are closest for UK-based observers on the evening of Thursday, 27 February, simultaneously visible in low-power binoculars.
