On Wednesday, 23 December, observers in the British Isles with clear skies can see the waxing gibbous 13-day-old Moon occult first-magnitude star Aldebaran in the constellation Taurus soon after 6:10pm GMT (see below for precise times). The reappearance of Aldebaran may also be seen after about an hour, weather permitting. This view is approximately six degrees high, corresponding to the field of view of a typical low-power binocular. AN graphic by Ade Ashford.If you have a clear sky in the east between 6pm and 7:15pm GMT on the evening of Wednesday, 23 December 2015, don’t miss out on seeing the rising 13-day-old waxing gibbous Moon pass in front of Aldebaran, the ‘Eye of the Bull’ in the constellation Taurus. Observers in the British Isles are ideally placed to observe this event — known as an occultation — which can be seen in larger binoculars (if one steadies the view by resting the elbows on a low fence or wall) and small telescopes. This is the fifth and final event of the year concerning this star for UK-based observers. All of the following times are GMT.
A computer simulation of the point on the Moon’s bright limb, near the oval lunar sea known as the Mare Crisium, where Aldebaran will reappear after occultation shortly before 7:13pm GMT as seen from the centre of the British Isles. AN graphic by Ade Ashford / SkySafari Pro.The instants of disappearance and reappearance of this first-magnitude star depend on where you live. For observers close to the heart of the UK, the advancing dark lunar limb (left-hand side of the Moon as seen with binoculars) passes over Aldebaran just before 6:14pm and the star reappears at the Moon’s bright hemisphere in line with the oval-shaped lunar sea known as the Mare Crisium, just before 7:13pm. For observers near London, Aldebaran disappears at 6:10pm and reappears a few seconds before 7:12pm. If you are observing in the vicinity of Edinburgh, the star winks out shortly before 6:18pm and pops back into view by 7:15pm.
As with any occultation observation, it pays to be setup at least 15 minutes before the predicted times of disappearance and reappearance so that you don’t miss out — plus it’s fun to see the advancing Moon glide ever closer to the star before it finally disappears from view. However, the reappearance of Aldebaran will be the most challenging aspect of this particular event since it occurs at the Moon’s bright hemisphere, so there’s a heightened sense of anticipation as you are unsure exactly when it will happen! Just keep monitoring the lunar limb close to the Mare Crisium. Clear skies!
Inside the magazine
You can find out more about observing this occultation of Aldebaran in the December edition of Astronomy Now in addition to a full guide to the night sky.
Observers in Western Europe should try to locate Venus low in the western sky an hour after sunset. The 3-day-old slim crescent Moon acts as a convenient guide, located some 12½ degrees (or half the span of an outstretched hand at arm’s length) to the upper left of the brightest planet on 18 April. Prominent star Aldebaran lies in the same low-power binocular field of view as the Moon too.
