The Astronomical Sky Above Edinburgh and Lothian in December 2024
Winter is coming for the Solstice occurs on 21 December at 9:21 am and heralds the start of the season of astronomical winter which lasts for the next 88 days, 23 hours and 40 minutes.
On the day of the Solstice, impress your friends by casting your longest shadow of the year.
The Sun leaves Ophiuchus (The Serpent Bearer) on 17 December at 4:34 pm and enters Sagittarius
(The Archer). Daylight shortens from 07:23 (7.392 hours) on 1 December to 07:04 (7.075 hours) on
31 December so we gain 19 minutes of night time by month’s end. In reality, we gain 26 minutes of
night time up to the Solstice (when the days get shorter) and then lose 7 minutes afterwards (when
the days get longer). On the Solstice, the Sun’s lowest altitude of the year will be 10.7° at 12:11
pm with the Sun some 147,164,044 km distant. This day, the shortest of the year, lasts 6 hours, 57
minutes and 40 seconds. The earliest sunset of the year is on 14 December at 3:36 pm and the latest
sunrise of the year is on 28 December at 8:48 am.
The (first) new Moon appears on 1 December at 6:21 am in Scorpius (The Scorpion) beginning
a new Lunar (synodic) month which will last 29 days, 16 hours and 5 minutes. The first quarter of
the new cycle shows up on 8 December at 3:27 pm in Aquarius (The Water Bearer). Lunar perigee
(closest to Earth) on 12 December at 1:30 pm finds the Moon some 365,384 km away from Earth—
around 19,016 km closer than average—subtending an angle of 32.7 arc-minutes. The full Cold Moon
makes an appearance on 15 December at 9:02 am in Taurus (The Bull). The Moon enters last quarter
on 22 December at 10:18 pm in Virgo (The Maiden). Lunar apogee (furthest from Earth) that occurs
on 24 December at 7:28 am and takes the Moon to 404,445 km away from Earth—around 20,045 km
further than average—subtending an angle of 29.5 arc-minutes. Finally, a second new moon appears
on 30 December at 10:27 pm in Sagittarius (The Archer) beginning another synodic month which
will last 29 days, 14 hours and 9 minutes. A second new Moon within the same calendar month is
sometimes called a Black Moon.
The waxing gibbous Moon conjuncts with the Pleiades star cluster (M45) on 13 December, being
separated by a mere 0.1°. Later in the month, on 20 December, the waning gibbous Moon will
conjunct with Regulus in Leo (The Lion) being separated by around 2.5°
.
For the inferior planets: Mercury appears in Ophiuchus (The Serpent Bearer) at the start and end
of the month but entertains a sojourn into Scorpius (The Scorpion) mid-month. The ‘Swift Planet’
recedes by 64,682,661 km but, contrarily, increases in brightness from +1.89 to -0.35 magnitudes
(7.86× in luminosity). It will be closest to Earth on 5 December, reaches (another) perihelion around
inferior conjunction (in front of the Sun) on 6 December, appears to reverse orbital direction on 15
December and reaches dichotomy (exactly half the surface is illuminated by the Sun) on 20 December.
Finally, on Christmas Day, Mercury reaches greatest western elongation (furthest angle from the Sun).
Observers hoping for a glimpse of the Mercury will have to wait until the second half of the month
when it re-emerges as a morning planet.
Venus begins the month in Sagittarius (The Archer) and ends in Aquarius (The Water Bearer)
but comes closer by 33,406,466 km. The ‘Brightest Planet’ increases in magnitude from -4.20 to -4.45
(1.26× in luminosity) over December and appears as a spectacular ‘evening star’ all month long.
Venus will be within 3° of the waxing crescent Moon as it sets on 4 December.
For the superior planets: Mars remains in Cancer (The Crab) all month but comes closer by
22,337,576 km and increases in brightness from -0.50 to -1.22 magnitudes (1.93× in luminosity). The
‘Red Planet’ crosses a stationary point on 6 December and so appears to reverse direction in orbit. It
rises earlier as the month goes on and offers excellent visibility for most of the night. On 18 December,
conjuncts within 2° of the waning gibbous Moon and will be occulted after it sets.
Jupiter remains in Taurus (The Bull) but recedes by 14,468,727 km and, so, decreases in brightness
from -2.81 to -2.74 magnitudes (0.94× in luminosity) over December. The ‘Gas Giant’ will be closest
to Earth on 6 December and at opposition on 7 December making for an excellent view. Being so
bright it is easy to find but, handily, it will be within within 4° of waxing gibbous Moon on the
evening of 14 December.
Saturn remains in Aquarius (The Water Bearer) all month but recedes by 74,497,144 km and
decreases in brightness from 0.94 to 1.05 magnitudes (0.90× in luminosity) over the month. The
‘Ringed Planet’ reaches eastern quadrature (making a right angle between Sun-Earth-Planet) on 4
December. On 8 December, it will be occulted by the first quarter Moon after it sets. Uranus is
in Taurus (The Bull) until 28 December when it crosses over into Aries (The Ram) and recedes
by 40,225,664 km. Neptune remains in Pisces (The Fishes) all month and recedes by 79,395,283
km. On 8 December, the ‘Blue Giant’ returns to a direct orbit and on 18 December reaches eastern
quadrature. Saturn, Uranus and Neptune remain as observable evening objects. As can be seen from
our sky map: Mars, Jupiter, Uranus, Neptune and Saturn all in the sky at the same time.
The Blaze Star (T CrB) has yet to live up to billing: providing another jewel in Corona Borealis
(The Northern Crown) of similar lustre to Polaris. This recurrent nova had been predicted to flare
again between last August through October but has yet to appear. There is still time as T CrB rises
after 2:30 am at the start of the month but gets earlier as December progresses. By Hogmanay, it
will rise around 12:30 am.
December entertains 7 meteor showers as detailed in the ephemeris but only 2 stand out. Feel
free to try and observe the others, though, but beware the large number of Starlink satellites that
may give a false positive for shooting stars!
The highly anticipated Geminid meteor shower, radiant from Gemini (The Twins), peak on the
night of 13–14 December for Edinburgh and Lothian. The radiant point is near the star Castor, one
of the heads of the Gemini twins. They are viewable after astronomical twilight ends (around 6 pm)
for the next 12 hours and reach high altitude so observability is excellent and they can produce up to
150 meteors per hour. The parent body is not a comet but the asteroid 3200 Phaethon and was the
first asteroid discovered in IRAS satellite data in 1983. However, the waxing gibbous, almost full,
Moon will attempt to spoil the show.
The Ursids, radiant from Ursa Minor (The Little Bear), are a poorer show compared to the
Geminids but will peak on 21–22 December and are circumpolar so viewable all night. The waning
gibbous Moon is illuminated to 58%. Look near the star Kochab and expect, maybe, 10 shooting
stars per hour. The parent comet is 8P/Tuttle discovered in 1858.
At the time of our sky map, some constellations visible are Perseus (The Hero) at zenith, Draco
(The Dragon) in the north, Cancer (The Crab) in the east, Pegasus (The Winged Horse) in the
west, and Eridanus (The River) in the south. The ecliptic hosts Leo (The Lion), Cancer (the Crab),
Gemini (The Twins), Taurus (The Bull), Aries (The Ram), Pisces (The Fishes) and Aquarius (The
Water Bearer).
The ‘Winter Hexagon’—Rigel in Orion (The Hunter), Aldebaran in Taurus (The Bull), Capella
in Auriga (The Charioteer), Pollux in Gemini (The Twins), Procyon in Canis Minor (The Lesser
Dog) and Sirius in Canis Major (The Great Dog)—rises in the south-east. This superstructure also
contains the ‘Winter Triangle’ comprising the stars Procyon and Sirius but joined by Betelgeuse in
Orion (The Hunter). Circumpolar constellations—always above the horizon—include Cepheus (The
King), Camelopardalis (The Giraffe), Cassiopeia (The Seated Queen) and Ursa Minor (The Lesser
Bear).
Phil Daly is a former employee of the Royal Observatory Edinburgh (now UKATC) on Blackford Hill.
He has worked on the UK's overseas telescopes in Hawaii (UKIRT, JCMT) and on large telescopes
at major astronomical observatories worldwide. He is currently part of an international collaboration
searching for optical counterparts to gravity wave events using multi-messenger astronomy.
