On the night of Wednesday, 14 September there’s a pretty rare circumstance to observe as the planet Uranus is occulted by the Moon. This exciting event can be seen from parts of Africa, Asia and Europe, including the whole of the UK. Amazingly, Uranus has been occulted by our satellite each month from somewhere on Earth since February and that amazing trend will continue for the rest of 2022, including another event, on 5 December, that’s visible across the UK
On Wednesday evening, Uranus and the Moon rise across the UK at around 8.55pm BST. Uranus disappears at the bright limb of 77-per cent-illuminated waxing gibbous Moon at about 10.27pm and 10.37pm BST (21:27 and 21:37 UT) from London and Edinburgh, respectively. By this time, the celestial pair has risen to about 12° to 13° above the eastern horizon.
Despite the Moon’s strong glare, a pair of binoculars and a small telescope will show the remote ice-giant off the bright limb (western limb of the Moon although its east on the sky) of the Moon. Uranus lies about 50’ east of the Moon as they rise, but the Moon quickly close the gap. It will be fascinating to observe as this happen and as the occultation begins Uranus won’t instantaneously disappear from view, taking a number of seconds to completely disappear behind the Moon. Depending on the ‘seeing’ conditions at the time, a high-power telescopic view could be spectacular.
Uranus is hidden behind the Moon until about 11.21pm and 11.27pm BST (22:21 and 22:27 UT), from London and Edinburgh, respectively, when it starts to reappear at the dark limb (eastern limb) of the Moon. Without the same degree of distracting glare as at the beginning of the occultation, it’ll be easier to see Uranus. Happily, by this time the Moon has climbed to a much more amenable altitude of 21° or so.
If you’re going to try to spot the precise moment Uranus starts to reappear, you’ll need to know roughly where on the Moon’s limb to look, especially if observing at high powers. The Handbook of the British Astronomical Association gives the Cusp Angle (CA), the angle of the event around the Moon measured from the nearest cusp. Uranus reappears at a CA of 77° and 70° at London and Edinburgh, respectively (from the northern cusp [see graphic]).
Another method is to use position angle (PA), the direction of an imaginary arrow in the sky measured in degrees from north (0°) through east (90°), south (180°) and west (270°). Uranus reappears at PA 268° and 275° from London and Edinburgh, respectively; so about due west at the Moon’s eastern limb.