Geminid meteors to impress as Halley’s Comet hits a milestone

Alan Pickup

Author: Alan Pickup

The maps show the sky at 21:00 GMT on the 1st, 20:00 on the 16th and 19:00 on the 31st.

Are you ready for what could be our best meteor display in years? The Geminids shower boasts the highest meteor rates of any of our annual showers and, for once, this year’s return occurs at a time when we have no interference from moonlight. What we do need, though, are fewer clouds than spoiled the also-prolific Perseids shower in August, and we had for October’s Orionids and even the Leonids two weeks ago.

Geminid meteors in 2022 from an ASE camera in Edinburgh

Geminid meteors diverge from a radiant point close to the star Castor in Gemini, though the meteors themselves appear in all parts of the sky. Our north star map shows Castor above the other Twin, Pollux, as they climb through the east to pass high across the meridian at 02:00. Meteor rates tend to grow as the radiant climbs higher, so post-midnight is better if, perhaps, colder.

The shower lasts from 4th to the 17th, with its broad peak predicted for around 19:00 on the 14th when more than 100 medium-slow meteors per hour might be counted by someone under ideal dark skies. Obviously, observed rates under polluted urban skies are a fraction of this value, but at least many Geminids are bright. Rather than a comet, the parent of the Geminids meteoroid stream is the asteroid Phaethon which passes closer to the Sun than any other known asteroid.

An Ursid meteor in 2022 from an ASE camera in Edinburgh, looking North

The month’s second meteor shower, the Ursids, derive from Comet 8P/Tuttle and reach their peak at about 04:00 on the morning of the 23rd, being active from the 17th to 26th. Its radiant point lies close to the star Kochab in Ursa Minor which hangs below Polaris in the north at our map times and stands level to the right of Polaris at the time of maximum. With moonlight to contend with, and with rates not much greater than 10 meteors/hour, this would be of interest only to die-hard meteor observers were it not for that fact that some tedious media commentators have taken to claiming that almost every shower, no matter how trivial, is going to “light up the sky”.

Following its last visit to the Sun in 1986, the most famous comet of all, Comet Halley, is predicted to reach the farthest point in its 76-year orbit at 01:00 on the 9th. It is then more than 5.2 billion km from the Sun, 35 times further than the Earth, and might just be visible through the very largest telescopes at magnitude 29 or so. Though its last reported sighting was in 2003, I suspect some well-endowed astronomers may be striving to better this record as you read this. It is next due to be closest to the Sun in the summer of 2061.

December brings our longest nights of the year as the Sun reaches its farthest south at the winter solstice, due at 03:27 GMT on the 22nd. It is then 23.44° south of the celestial equator and climbs no more than 11° above Edinburgh’s horizon during the day. Our sunrise/sunset times vary from 08:19/15:44 on the 1st, to 08:42/15:40 on the 22nd and 08:44/15:47 on the 31st.

Jupiter is conspicuous in the east as the night begins, climbing into prime position in the middle of our southern sky by our star map times before sinking westwards to set in the west-north-west before the first rays of dawn. It lies 11° south of the star Hamal in Aries and creeps slowly westwards against the stars until the final hours of the year when its motion appears to reverse at a so-called stationary point.

The giant planet dims a little from magnitude -2.8 to -2.6 this month, its cloud-belted disk appearing 46 arcseconds wide through a telescope at midmonth.

The second-largest planet, Saturn, lies in Aquarius and is the brightest and rather solitary object (magnitude 0.8 to 0.9) in our lower southern sky as the night begins. It then sinks into the south-west by our map times and sets another 90 minutes later. The north face of its rings is tipped 10° towards us at present and they span 38 arcseconds around the 17 arcseconds Saturnian disk.

Uranus and Neptune, at magnitudes of 5.6 and 7.9, may be glimpsed through binoculars several degrees to the east of Jupiter and Saturn respectively.

Venus continues as a brilliant morning object to the south of east where it stands less than 5° above and left of Virgo’s leading star, Spica, on the 1st. As it tracks southwards and eastwards and through Libra, however, its altitude in the south-south-east at sunrise falls from 25° to 15° by the year’s end. It also recedes and dims slightly from magnitude -4.2 to -4.1, the diameter of its dazzling gibbous disk shrinking from 17 to 14 arcseconds.

With Mars out of sight beyond the Sun, Mercury, too, is poorly placed for our latitudes this month. The innermost planet hugs our south-western horizon after sunset until midmonth before passing through inferior conjunction on the Sun’s near side on the 22nd. We might just glimpse it on the final two mornings of the year after it rises ninety minutes before the Sun and stands some 20° to the left of Venus and 9° lower.

The Moon passes above Regulus in Leo on the night of the 3rd-4th and reaches last quarter on the 5th. It is a waning 15% sunlit crescent to the right of Venus and below-left of Spica on the 9th and new on the 12th. Emerging into our south-western evening sky, its crescent may be found below-right of Saturn on the 17th and to Saturn’s left on the 18th. First quarter arrives on the 19th when it stands below the Circlet of Pisces and close to Neptune. Look for it to the right of Jupiter on the 21st and above-left of Jupiter on the 22nd. Full Moon, the so-called Cold Moon, occurs in Gemini on the 27th and the year ends with the Moon once more near Regulus.

Our charts plot the oval smudge of the famous galaxy M31 in Andromeda just a few degrees to the south-west of overhead as Taurus and the Pleiades stand in the south-east and level with Jupiter. Orion lies below Taurus and is unmistakable astride the meridian four hours later. Look below Orion’s 3-star Belt for the Sword of Orion where the hazy patch of the Orion Nebula, obvious through binoculars, is the sky’s best-known region for the formation of new stars.

For lucky astronomers along a narrow path across southern Europe, Orion’s most famous star, the red supergiant Betelgeuse in the Hunter’s shoulder, is predicted to disappear on the early morning of the 12th when it is hidden for just a few seconds by the asteroid Leona, around 300,000 times fainter.

Comet 12P/Pons-Brooks taken by Denis Buczynski

The two telescopic comets to watch this month are Comets 12P/Pons-Brooks and 62P/Tsuchinshan.

Pons-Brooks has earned the title of Devil Comet because outbursts of material from its nucleus have given it a horned-like appearance from time to time, leading also to large changes in its brightness which have been nicely monitored by observers in the Astronomical Society of Edinburgh. As the month begins it may be near the ninth magnitude as it tracks eastwards through Lyra, passing only 0.5° south of Vega on the evening of the 6th when it lies 380 million km from the Earth and 347 million km from the Sun. It may well become a naked-eye object before it swings too far south to be seen from Scotland ahead of its perihelion, 117m km from the Sun, next April.

Comet Tsuchinshan, also around the ninth magnitude, is observable in our morning sky as it moves east-south-eastwards through Leo. It lies 189 million km from the Sun at perihelion on Christmas Day.

Diary for 2023 December

  • 1st 04h Moon 1.6° S of Pollux
  • 2nd 05h Moon 4°N of Praesepe
  • 4th 01h Moon 4° N of Regulus
  • 4th 14h Mercury furthest E of Sun (21°)
  • 5th 06h Last quarter
  • 6th 17h Comet Pons-Brooks 0.5° S of Vega
  • 8th 15h Moon 2.3° N of Spica
  • 9th 01h Comet Halley furthest from Sun (5.26 billion km)
  • 9th 17h Moon 4° S of Venus
  • 13th 00h New Moon
  • 14th 05h Moon 4° S of Mercury
  • 14th 19h Peak of Geminids meteor shower
  • 17th 22h Moon 2.5° S of Saturn
  • 19th 19h First quarter
  • 22nd 03:27 Winter solstice
  • 22nd 14h Moon 2.6° N of Jupiter
  • 22nd 19h Mercury in inferior conjunction on near side of Sun
  • 23rd 04h Peak of Ursids meteor shower
  • 24th 08h Moon 1.0° S of Pleiades
  • 25th 05h Moon 9° N of Aldebaran
  • 27th 01h Full Moon
  • 28th 13h Moon 1.7° S of Pollux
  • 29th 13h Moon 4°N of Praesepe
  • 31st 10h Moon 4° N of Regulus
  • 31st 15h Jupiter stationary (motion reverses from W to E)

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 30 November 2023, with thanks to the newspaper for permission to republish here.