The Sky Above You – December 2023
By Duncan Lunan
On December 1st the Moon will be in line with Castor and Pollux in Gemini. It will be New on December 12th, and Full on December 27th, when it passes below Castor and Pollux. It’s near Venus on the 9th and near Jupiter on the winter solstice, December 22nd (see below).
In the 1960s. an alleged UFO contactee called Truman Betherum claimed he had multiple contacts with a flying saucer from the planet Clarion, which was permanently out of sight beyond the Moon. The L2 point in the Earth-Moon system does exist, on the far side of the Moon from us, and was visited by the Chinese Chang’e 2 spacecraft on its way to the asteroid Toutatis in 2010, more recently by Chang’e 5-T1 in 2014. But if a habitable-sized planet existed at L2, it would have been visible round the edges of the Moon all along. Reasons for mentioning this now will be apparent below.
A mystery about Chang’e 5-T1 is deepening. On 3rd March 2022, an unidentified booster which had been orbiting in the Earth-Moon system crashed into the Moon, impacting near Hertzsprung crater on the lunar Farside. There were only two possible candidates: the Falcon 9 booster which launched the DISCOVR spacecraft, now returning images of the Earth from the L1 point between us and the Sun, or else Chang’e 5-Ti’s, though Chinese authorities insist that it re-entered Earth’s atmosphere, separately from the spacecraft. Nevertheless, researchers at the University of Arizona have eliminated the Falcon 9 possibility, and optical evidence supports the Chinese origin. It also has emerged that the mystery object was tumbling stably, end-over-end, indicating a large mass on the front, balancing the engines at the rear. Lunar Reconnaissance Orbiter has photographed the impact point and found a double crater, which backs that interpretation. But the Chinese authorities insist that the instruments on the booster massed only 27 kilograms, which raises the question, what else was it carrying that’s such a big secret?
The planet Mercury is very low in the evening sky in early December, at maximum elongation on the 4th, when it sets at 5 p.m., and disappearing by mid-month, passing inferior conjunction on this side of the Sun on the 22nd. On the 28th Mercury passes Mars, both too close to the Sun to be visible, but Mercury will reappear very low in the morning sky by the 31st.
A remarkable insight into the early history of Mercury was announced by the Planetary Science Institute in Tucson, Arizona, on November 17th. The Messenger orbiter in 2011-2015 discovered strange pits in the floors of impact craters there, clearly formed by material which had risen to the surface, or been exposed, and had then evaporated. But what could it be? Speculation ranged around light metals such as lead, which would be liquid under the midday Sun on Mercury. It turns out to be salt, which apparently had flowed on an older surface, now buried, in the form of glaciers – found on Earth, but uncommon. The discovery has been made in a polar region called Borealis Chaos, where the shockwaves of multiple impacts elsewhere have been focused and torn up the surface, after which fresh impacts on it have uncovered a deeper layer dating back to the early history of the planet. At that time, it seems, Mercury already had its remarkable 2:1 lock between its year and its day; but it also had an atmosphere and a salty ocean from which the glacial salt deposits condensed and flowed during the long periods of darkness. Most press headlines have concentrated on how salt glaciers on Earth harbour life, in the form of ‘extremophile’ microorganisms which have evolved to tolerate those conditions, but it’s not likely that life on Mercury could have begun or evolved to such a specialised form before the warming Sun made oceans there impossible. What happened on Mars, where extremely salty water formed on some crater floors in the distant past, and may still flow down the inner walls of craters in summer, may be another matter.
Venus rises at 4 a.m. between Libra and Virgo, still bright, near the Moon on the morning of the 9th.
Mars is still out of sight beyond the Sun, until next spring. On November 18th Mars was at superior conjunction, directly opposite to Earth on the far side of the Sun. It happens roughly every 25 months, as the Earth pursues Mars around the Sun, and requires minimising communications between Earth and spacecraft in orbit around Mars or on the surface. But this will be the first time, for them, that Mars will go directly behind the Sun, actually behind the solar disc. For example Europe’s Mars Express entered orbit there on December 25th 2003, and is about to celebrate 20 years of successful operation, ten times longer than expected – but it’s never seen this happen before. The last such ‘Transit of Earth’, title of a 1971 short story by Arthur C. Clarke, was on May 11th 1984. It’s usual for spacecraft operation to be paused in ‘conjunction season’, but this time it will cease altogether for several days. Normal service is expected to resume on December 2nd.
On November 1st, the Lucy spacecraft made its predicted flyby of the asteroid Dinkinesh, on the inner edge of the Main Asteroid Belt. In September, I wrote ‘who knows what surprises it will have for us?’ The first big surprise was that despite its small size, Dinkinesh had a satellite. Before the Galileo probe’s fly of asteroid Ida revealed its satellite Dactyl in 1993, professional and amateur observers had been in dispute over whether asteroids could have satellites, and the amateurs were proved right. ‘Dinkinesh’ means ‘You are marvellous’ in the Amharic language of Ethiopia, and it’s their name for Lucy the human-ancestor fossil, after which the spacecraft is named, but it didn’t take long for the suggestion that the satellite should be called ‘Dinkytoy’. From the spectroscopic data, it was clear that Dinkinesh and its satellites are made of the same rock, without the colour differences which suggest Ida and Dactyl had separate origins. Then NASA revealed a bigger surprise: Dinkytoy itself was double, a ‘contact binary’. It remains uncertain whether its components are touching, like the lobes of asteroid Arrakoth in the Kuiper Belt, or orbiting closely around another. What appeared to be sunlit ridges on the right-hand side of Dinkytoy may be glimpses of ‘Dinkytoy 2’ around it. But it’s not at the L2 point, as ‘Clarion’ was alleged to be for the Earth and Moon. Lucy’s film of Dinkytoy passing across the face of Dinkinesh doesn’t show Dinkytoy 2, so it must be hidden behind, between Dinkinesh and Dinkytoy, and possibly starting to emerge in the Dinkytoy discovery image, taken at closest encounter.
Jupiter in Aries sets at 3.30 a.m., and the Moon passes Jupiter on December 22nd, at the winter solstice. On the 31st Jupiter reaches its apparent ‘stationary point’, beginning to move eastward against the stars, after opposition when the Earth passed it in November.
Saturn in Aquarius sets at 10.00 p.m., and is passed by the crescent Moon on December 17th.
Uranus in Aries sets at 5 a.m.. Uranus appears near the Moon on the 23rd.
Neptune is on the boundary of Aquarius and Pisces, setting around midnight, and coming to its ‘stationary point’ on December 7th, after which it will begin to move eastward. Neptune is near the Moon on December 19th, and will be occulted by it as seen from south Australia.
The Andromedid meteor shower peaks on the night of 2nd-3rd December, and this year there’s a chance of a big display. The parent Biela’s Comet broke up in 1846, with meteor showers for a few subsequent years, but this year the comet is expected to meet a dust stream emitted in 1649, when the comet was still in one piece. The stream may generate as many as one meteor per minute, before the Moon rises after midnight, when fewer meteors will be visible.
The Geminid meteor shower from the asteroid Phaethon peaks on the night of 13th-14th December, with no interference from moonlight. While many asteroids have fragmented, either recently or in the remote past, probably all of them with dust trails, Phaeton’s is the only one which happens to cross the Earth’s orbit at present. When it was discovered in 1983, in data compiled by the Infra Red Astronomy Satellite IRAS, Fred L. Whipple was first to realise that its orbit was the same as the Geminids’. Several other asteroids have similar orbital elements, leading to suggestions of a breakup around 2700 BC – interesting for several reasons, but not least because it was the suggested date for the Henbury meteorite craters near Alice Springs in Australia. That was odd because the Henbury impactors were fragments of a nickel-iron meteorite, like the one which formed Barringer Crater in the USA, yet Phaethon and its meteors appear to be rock. And yet, in my childhood I saw a winter display of bright green meteors, which might suggest a metallic composition if they were Geminids. What we need is a close look at Phaethon, and it may be provided by Japan’s DESTINY+ probe (Demonstration and Experiment of Space Technology for INterplanetary voYage, scheduled for launch in 2025 and rendezvous with Phaethon in 2029, which is going to be a very busy year for asteroid studies, as noted last month.
On December 9th Halley’s Comet reaches aphelion, its furthest point from the Sun. Its orbital period averages 76 years, subject to perturbations by the major planets, and in recent years I’ve detected some uncertainty in other publications about just when aphelion will be, In 1986 I had to organise public showings of the Comet at Airdrie Observatory, with great difficulty because it was just above the floodlit town hall, and although North Lanarkshire Council had directed that the public should be shown it, there was no chance that the lights could be turned off. I’m not sure what I shall be doing when it returns in 2061, because I shall then be 116 years old.
Duncan Lunan’s recent books are available through Amazon. For more information see Duncan’s website, www.duncanlunan.com.
The Sky Above You
By Duncan Lunan
About this Column
I began writing this column in early 1983 at the suggestion of the late Chris Boyce. At that time the Post Office would allow 1000 free mailings to start a new business, just under the number of small press newspapers in the UK at the time. I printed a flyer with the help of John Braithwaite (of Braithwaite Telescopes) offering a three-part column for £5, with the sky this month, a series of articles for beginners, and a monthly news feature. The column ran from May 1983 to May 1993 in various newspapers and magazines, but never in more than five outlets at a time, although every one of those 1000-plus papers would have included an astrology column. Since then it’s appeared sporadically in a range of publications including The Southsider in Glasgow and the Dalyan Courier in Turkey, but most often, normally three times per year, in Jeff Hawke’s Cosmos from the first issue in March 2003 until the last in January 2018. It continues to appear monthly in Troon's Going Out and Orkney News. Enquries from other outlets welcomed!
The monthly maps for the column were drawn for me by Jim Barker, based on similar, uncredited ones in Dr. Leon Hausman’s “Astronomy Handbook” (Fawcett Publications, 1956). Jim had to redraw or elongate several of them because they were drawn for mid-US latitudes, about 40 degrees North, making them usable over most of the northern hemisphere. The biggest change needed was in November when only Dubhe, Merak and Megrez of the Big Dipper, as the US version called it, were visible at that latitude. In the UK, all the stars of the Plough are circumpolar, always above the horizon. We decided to keep an insert in the January map showing the position of M42, the Great Nebula in the Sword of Orion, and for that reason, to stick with the set time of 9 p.m., (10 p.m. BST in summer), although in Scotland the sky isn’t dark then during June and July.
To use the maps in theory you should hold them overhead, aligning the North edge to true north, marked by Polaris and indicated by Dubhe and Merak, the Pointers. It’s more practical to hold the map in front of you when looking south and then rotate it as you face east, south and west. Some readers are confused because east is on the left, opposite to terrestrial maps, but that’s because they’re the other way up. When you’re facing south and looking at the sky, east is on your left.
The star patterns are the same for each month of each year, and only the positions of the planets change. (“Astronomy Handbook” accidentally shows Saturn in Virgo during May, showing that the maps weren’t originally drawn for the Hausman book.) Consequently regular readers for a year will by then have built up a complete set of twelve.