The long-awaited opposition of Mars on 8 December is a great way to put the icing on top of another great observing year. Considering its proximity to Earth, an average distance of 225 million kilometres, Mars appearing at or close to its best is a somewhat elusive event. The red planet comes to an opposition-best (when it lies directly opposite the Sun in the sky) on alternate years only (its mean synodic period is 780 days), the last opposition occurring on 13 October 2020. Therefore, any opposition of Mars is to be cherished.
However, this time around there’s a tasty cherry on top of the icing in the form of an occultation of Mars by the full Moon on the morning of 8 December, an event not to be missed.
Mars is at opposition the night of 7/8 December (at 05:36 UT), when it shines brilliantly at magnitude –1.9, only half a magnitude fainter than Jupiter, and offers telescopic observers a disc spanning a very healthy 17 arcseconds. Riding high among the stars of Taurus, the Bull there’s no issues with poor altitude unlike at the 2020 opposition, as the red planet lies 20° higher in the night sky. Mars is above 30° in altitude from about 7.30pm to 5am GMT, peaking at an elevation of around 60° when it crosses the southern meridian at midnight or so.
A small telescope to resolve Mars’ major dark markings, and owner’s of medium- to large-aperture telescopes and high-resolution imaging set-ups to gather scientifically-valuable data. Mars’ most famous feature, the ‘V’ shaped Syrtis Major, finally rotates into view at Mars’ following limb from around 3am GMT on opposition night. However, you’d better be quick when observing or imaging it as here comes the Moon!
Mars hidden by the Moon!
An occultation of a planet by the Moon that’s visible across the whole of the UK is not a common event and is one to pull out all the stops to try to observe it.
At about 7pm GMT on 7/8 December, Mars and the Moon are well up in the east and lie 4.2° apart, providing a fine sight with the naked eye and through a pair of 10 x 50 binoculars. As the evening wears on, check intermittently on their progress while you’re observing or imaging Mars and you’ll see the Moon closing in on Mars. By 3am Moon has closed within a degree or so of the red planet, the pair now lying half way up the western sky.
Scotland will be first to witness the occultation; from Edinburgh, the Moon starts to move over Mars at about 4.52am GMT, with the event beginning at about 5am GMT for observers in London. Mars and the Moon are around 30 and 27 degrees up from Edinburgh and London, respectively. As with all occultation events, be sure to be ready to observe at least a few minutes before.
It’s a shame the Moon is at full phase (4.08am GMT) as observers will have to contend with its powerful glare, but naked-eye observers should be able to get a good view by hiding the Moon with your hand. Unlike when a star winks out instantaneously, Mars, with its 17.1” disc, takes its time. High-power telescopic views will be especially spectacular, as it will be fascinating to watch while Mars takes about 35 seconds or so to completely disappear behind the Moon.
Mars is accompanied by star, magnitude +9.6 HIP 23032, which lies about half a degree to the south-west and is occulted seconds before Mars.
Mars is hidden from view for an hour or so, reappearing at about 5.53am and shortly before 6am from Edinburgh and London, respectively.