During the first
three weeks of the month, the Sun is travelling eastwards through the constellation of Ophiuchus and crosses the border into Sagittarius at around midday on the 18th. The earliest sunset of the year is on the 12th, and the latest sunrise
is on the 31st. Between them lies the Winter Solstice, which this year takes place on December 21st at 22h23. The Earth-Sun distance at this time is 147,160,039 km. The Earth’s north pole is tilted as far away as it can be
from the Sun (23°26’) and this day is the official start of winter, a season which lasts 88.98 days in the northern hemisphere, and of course summer in the south.
The Moon is at apogee, its furthest from the Earth, on the 12th at 12h00 and at perigee, its
nearest to the Earth on the 24th at 09h00.
December’s New Moon occurs at 07h21 on the 7th
in Ophiuchus, passing 2° to the north of the Sun.
First Quarter Moon on the 15th at
11h50 is in Aquarius, near Mars.
Full Moon at 17h49 on the 22nd, is in northern Orion, 5° east of zeta
Tauri, the star which marks the tip of the Bull’s southern horn. Castor and Pollux, in Gemini, lie some 20° to the left of the Moon. This is the very highest Full Moon of 2018.
The Last Quarter Moon occurs on 29th at 09h35 in the constellation of Virgo, between the stars Zaniah and Porrima.
It may be possible to see Earthshine on the waning crescent during the first week and the last two days of the month, and on the waxing crescent Moon’s dark hemisphere from the 8th
at its greatest angular elongation west of the Sun (21°) on the 15th, giving us the best opportunity to observe this, the closest planet to the Sun. At the time of elongation, it rises two hours before the Sun, and may be sought in the early
morning sky before sunrise. You should look some 5° above the SE horizon. Binoculars are a help, as is the waning crescent Moon, which at 07h on the 5th, lies some 7° to the upper right of Mercury, with Venus lying 20° above and to the
right of the Moon. So on this day lies an opportunity to see both of the two inner planets, and our nearest neighbour in space, the Moon.
Venus, or as it was known to the Ancients, “Phosphorus”, the “Morning Star”, shines resplendently in the pre-dawn sky around Christmas, and may encourage people to think once again about the ‘Star of Bethlehem’.
There is an article devoted to this on another page in these Sky Notes; use the Menu to find it. Venus rises at around 04h throughout the month, and the bright star near to it (though very much dimmer than Venus of course) is Spica (alpha Virginis), brightest
star in Virgo. The waning crescent Moon, with earthshine on its night hemisphere, may be seen approaching Venus, on the 3rd, both some 20° above the SE horizon. At 07h on this day, the celestial pair are separated by 7° of arc The next day
the two are just 5° apart, with Venus lying to the right of the lunar crescent. On both days, a lovely spectacle on show in the early morning winter sky.
Mars continues to fade as it climbs higher through the constellation of Aquarius. The planet is visible for over seven hours after the Sun sets and is comparable in brightness to Capella in the constellation of Auriga.
As the month begins, the planet has a magnitude of 0.0. By the end of the month, Mars has moved into the constellation of Pisces, and has faded to magnitude +0.4, which is a little brighter than Altair in Aquila. Mid-month, Mars culminates in the south at
just before 18h00 at an altitude of just over 30°. On the 14th, Mars and the broad waxing crescent Moon (almost first quarter) are in conjunction about 5° apart. There is an interesting conjunction between Mars and Neptune on the 7th;
the closest approach is at 14h00. From the UK the best time to observe the pair is at 18h00, when they cross the south meridian. Using binoculars or a telescope, Neptune at magnitude +7.9 (below naked eye visibility) lies 6 minutes of arc (0.1°) to the
southwest of Mars (lower right through binoculars), Mars has a magnitude of +0.1 at the time.
Jupiter was in conjunction
with the Sun on 26th November, and throughout December starts to reappear in the morning sky, and by the end of the month rises at 06h, some 2 hours before the Sun. Search for it using binoculars before the Sun rises in the SE. Jupiter starts in
the constellation of Scorpius, but moves eastwards into Ophiuchus during the middle of the month. There is a good opportunity to see Jupiter and Mercury in conjunction, some 5° above the horizon as twilight brightens in the SE sky, on the 21st,
when just before 08h the two planets are just less than 1° apart. Mercury at magnitude -0.5, lies above Jupiter, the brighter of the two at magnitude -1.7. A beautiful celestial spectacle if the SE horizon is clear. Venus, much brighter, at magnitude -4.7,
lies 25° to the upper right of the pair in the direction of Spica.
A glimpse through binoculars at Jupiter will readily show its flattened disc, and if your binoculars are well focussed and firmly
fixed, you will be able to see the Galilean satellites as they change position from night to night. The configuration of Jupiter and its four major satellites may be seen on the front page of these Sky Notes.
At the beginning of December, Saturn sets two hours after the Sun at around 17h45, but at the end of the month it sets with the Sun. The best time to observe Saturn is therefore during
the first half of December. It lies in the constellation of Sagittarius, so to identify it look within 5° of the SW horizon at around 17h. On the 9th at about 16h45, you may be able to see the thin waxing crescent Moon 5° to the upper left
of Saturn, but a clear horizon in that direction will be necessary in order to spot the magnitude +1.3 planet and the “hairline” crescent of the Moon.
Uranus lies on the Pisces/Aries border, culminating (crossing the south meridian) at an altitude of 47° at around 20h mid-month. The +5.7 magnitude planet lies 1.5° north of the star Torcularis Septentri (omicron
Piscium), a magnitude +4.26 star.
A star chart showing the position of Uranus is to be found on the ‘REMOTE
PLANETS’ page. Uranus is on the threshold of naked eye visibility.
Neptune, in the constellation of Aquarius,
culminates at 17h15 mid-month. The +7.9 magnitude planet lies 2° to the east of lambda Aquarii, a star of visual magnitude +3.74. Mars is in the vicinity of Neptune and the conjunction between the two planets on the 7th has already been mentioned
in the Mars paragraph.
It should be looked for using binoculars or a small telescope. Use the star chart on the REMOTE PLANETS page
to identify this remote world.
The maximum of the Geminid meteors takes place on the 14th at 08h00. Geminids
may be seen from the 8th to the 17th, and this year is a favourable one for the observation of this, the richest of the annual showers. (Weather permitting of course!) These bright fast moving shooting stars are associated with
asteroid 3200, Phaethon, the remains of a spent comet. Geminids tend to be most numerous around 02h00 when Gemini, their point of origin, is almost overhead. On good nights it is possible to see up to 100 meteors an hour. This shower produces a good proportion
of bright events.
Peaking overnight on the 22nd/23rd is the Ursid meteor shower (fragments of
comet Tuttle), which produces about 10 meteors an hour, with occasional outbursts resulting in a greater number. Conditions this year are unfavourable as the Moon is Full. The radiant (point of origin) of the meteors is in Ursa Minor, some 12° from
the celestial pole.
Constellations visible in the south around midnight, mid-month, are as follows: Lepus the Hare, Orion, Taurus and Auriga the Charioteer.
All times are GMT 1° is one finger width at arm’s length.
DECEMBER EVENTS SUMMARY
Phenomena of the month : December 2018
Times are given in standard time for SCARBOROUGH (0° 25' 5" W, 54°
16' 30" N, zone UT).
Date Hour Description of the phenomenon
yyyy mm dd hh:mm
2018 12 01 17:49 Maximum of the
variable star eta Aquilae
2018 12 03 01:09 Minimum of the variable star Algol (beta Persei)
2018 12 04 05:33 Opposition of the asteroid 128 Nemesis with the Sun (dist. to
the Sun = 2.507 AU; magn. = 10.5)
2018 12 05 14:45 Maximum of the variable star delta Cephei
2018 12 05 21:58 Minimum of the variable star Algol (beta Persei)
2018 12 07 07:20 NEW MOON
2018 12 07 12:53 Opposition of the asteroid 433 Eros with the Sun (dist. to the Sun = 1.208 AU; magn. = 9.7)
2018 12 07
14:08 Close encounter between Mars and Neptune (topocentric dist. centre to centre = 0.0°)
2018 12 07 21:59 Close encounter between Saturn and M 22 (topocentric dist. centre to centre = 1.2°)
2018 12 08 18:47 Minimum of the variable star Algol (beta Persei)
2018 12 08 19:22 Opposition of the asteroid 40 Harmonia with the Sun (dist. to the Sun = 2.230 AU; magn. = 9.4)
2018 12 08 22:03 Maximum of the variable star eta Aquilae
2018 12 09 05:28 Meteor shower : Monocerotids (2 meteors/hour at zenith; duration = 20.0 days)
2018 12 09 17:42 Maximum of the variable star zeta Gemini
2018 12 10 09:39 Minimum of the variable star beta Lyrae
2018 12 10 15:06 Opposition of the asteroid 80 Sappho
with the Sun (dist. to the Sun = 2.132 AU; magn. = 10.3)
2018 12 10 23:33 Maximum of the variable star delta Cephei
2018 12 10 23:54 Maximum of the variable star Mira (omicron
2018 12 11 00:02 Maximum of the variable star khi Cygni
2018 12 11 15:36 Minimum of the variable star Algol (beta Persei)
12 12 04:19 Meteor shower : Sigma Hydrids (3 meteors/hour at zenith; duration = 12.0 days)
2018 12 12 12:25 Moon at apogee (geocentric dist. = 405177 km)
2018 12 12 23:33
Comet 46P Wirtanen at its perihelion (dist. to the Sun = 1.055 AU; magn. = 3.9)
2018 12 14 04:24 Opposition of the asteroid 354 Eleonora with the Sun (dist. to the Sun = 2.636 AU; magn. = 10.2)
2018 12 14 08:24 Meteor shower : Geminids (120 meteors/hour at zenith; duration = 12.0 days)
2018 12 14 12:25 Minimum of the variable star Algol (beta Persei)
12 14 17:43 Close encounter between the Moon and Neptune (topocentric dist. centre to centre = 3.6°)
2018 12 15 11:49 FIRST QUARTER OF THE MOON
2018 12 15 18:00 GREATEST
WESTERN ELONGATION of Mercury (21.2°)
2018 12 16 02:19 Maximum of the variable star eta Aquilae
2018 12 16 02:42 Meteor shower : Coma Berenicids (3 meteors/hour at zenith;
duration = 11.0 days)
2018 12 16 08:21 Maximum of the variable star delta Cephei
2018 12 17 09:14 Minimum of the variable star Algol (beta Persei)
2018 12 19 00:33 Beginning of occultation of 73-xi2 Cet (magn. = 4.30)
2018 12 19 01:14 End of occultation of 73-xi2 Cet (magn. = 4.30)
2018 12 19 21:17 Maximum of
the variable star zeta Gemini
2018 12 20 01:01 Meteor shower : Dec. Leo Minorids (5 meteors/hour at zenith; duration = 61.0 days)
2018 12 20 06:03 Minimum of the variable
star Algol (beta Persei)
2018 12 21 17:09 Maximum of the variable star delta Cephei
2018 12 21 17:59 Close encounter between Mercury and Jupiter (topocentric dist. centre
to centre = 0.8°)
2018 12 21 19:23 Beginning of occultation of 104 Tau (magn. = 4.91)
2018 12 21 20:04 End of occultation of 104 Tau (magn. = 4.91)
2018 12 21 22:23 WINTER SOLSTICE
2018 12 22 05:59 Close encounter between Mercury and Antares (topocentric dist. centre to centre = 6.0°)
12 22 16:41 Meteor shower : Ursids (10 meteors/hour at zenith; duration = 9.0 days)
2018 12 22 17:05 Beginning of occultation of 62-chi2 Ori (magn. = 4.64)
2018 12 22 17:43
End of occultation of 62-chi2 Ori (magn. = 4.64)
2018 12 22 17:49 FULL MOON
2018 12 23 02:53 Minimum of the variable star Algol (beta Persei)
2018 12 23 06:34 Maximum of the variable star eta Aquilae
2018 12 23 08:14 Minimum of the variable star beta Lyrae
2018 12 23 18:58 Close encounter between Jupiter
and Antares (topocentric dist. centre to centre = 5.2°)
2018 12 24 09:52 Moon at perigee (geocentric dist. = 361061 km)
2018 12 25 05:22 Close encounter between the Moon
and M 44 (topocentric dist. centre to centre = 1.3°)
2018 12 25 07:45 Beginning of occultation of 47-delta Cnc, Asellus Australis, (magn. = 3.94)
2018 12 25 23:42 Minimum
of the variable star Algol (beta Persei)
2018 12 26 16:00 Venus at its perihelion (distance to the Sun = 0.71845 AU)
2018 12 27 01:56 Maximum of the variable star delta Cephei
2018 12 28 02:46 Opposition of the asteroid 6 Hebe with the Sun (dist. to the Sun = 2.221 AU; magn. = 8.4)
2018 12 28 20:31 Minimum of the variable star Algol (beta Persei)
2018 12 29 09:34 LAST QUARTER OF THE MOON
2018 12 30 00:52 Maximum of the variable star zeta Gemini
2018 12 30 10:48 Maximum of the variable
star eta Aquilae
2018 12 31 17:20 Minimum of the variable star Algol (beta Persei)
(Using Coelix Software)