The night sky in December 2018

posted 30 Nov 2018, 09:58 by Pete Collins   [ updated 30 Nov 2018, 12:07 ]
by Anne Holt

Sunrise      1st:    08.01       31st:    08.25
Sunset       1st:    15.53       31st:   15.59

Astronomical darkness
1st:  18.02 to 05.54       31st:  18.09 to 06.14

Latest Sunrise    30th  (08.25 from 28th - 31st)
Earliest Sunset   13th  (15.49 from 9th -17th)

Winter Solstice: 21st at 22.22.  This day is 9hrs 33mins shorter than at the Summer Solstice.
The shortest day is also on the 21st - 7hrs 28mins 29seconds.  The 22nd is less than 1 second longer.

New Moon:  7th at 07.20     Full Moon:  22nd at 17.48
Lunar apogee  12th at 12.27  (distance of  405176km)
Lunar perigee  24th at 09.53  (    "          "   361059km)

December's full Moon is known as the Cold Moon, no explanation needed. The Old English/Anglo-Saxon names are also self explanatory - The Moon before Yule or the Full Long Nights Moon.
In December, because of the angle of the ecliptic, the full Moon takes its highest path across the sky, opposite the lowest position of the Sun. The Winter Solstice this year is only just over 19 hours before the full Moon.

Highlights

Lots of lovely dark nights (fingers crossed for some cloud free skies) about 12 hours of astronomical darkness throughout the month.  We have the Winter Solstice and the shortest day - or, as astronomers prefer to think of it, the longest night, with 12 hours more astro darkness than in June.
There is one major meteor shower, the Geminids, often considered to be the most reliable of all, and several minor ones.
There should be a naked eye comet mid month, though it's failing to live up to the spectacular predictions made earlier in the year and will probably only be visible to the naked eye from a dark sky site - if that.
There are some bright early evening passes of the International Space Station in the first half of the month.
And we have a Christmas Star in the East! Venus is shining brightly in the morning sky in December. It will be slightly past its best by 25th but will still be brilliant, maybe bright enough to be seen in daylight, if you know where to look. It isn't recommended that you try to follow it, however, even if you do happen to have a camel and some gift wrapped gold, frankincense or myrrh.  It's unlikely to lead you to Bethlehem and, anyway, you'd be more than 2000 years late. And you would miss your Christmas lunch.

Constellations

Orion, with the stars of his belt pointing down to the brightest star in the sky, Sirius, is now well above the horizon by midnight, and is a beautiful sight especially from a dark sky site.  By month end these will be visible from 10pm - weather permitting.  Taurus and the Pleiades precede him across the sky.

Gemini, including the 'twins' Castor and Pollux, and Auriga with the bright Capella are also very prominent. Aries and Pisces, while not particularly bright - or often not even visible in our light polluted skies - are both quite high this month.

Perseus, Andromeda and the Great Square of Pegasus  are also well placed for most of the night. The Plough starts the night quite low in the Northern sky, with Cassiopeia high overhead.  Because of the long winter nights, these last two will have changed places before dawn as they rotate around the celestial north pole.

Planets

Mercury: in Libra. mag 3.0
A morning object, but not easily seen in December, especially at the beginning and end of the month. On 1st it rises at 07.04 just under an hour before the Sun but separated from it by only 8 degrees.  On 4th it is 2 degrees above the horizon at dawn and the following morning, when it will have brightened to mag 0.8, is just 7.5 degrees west of the 4% Moon as they rise about an hour before Sunrise.  It reaches greatest western elongation on 15th, when it will be at mag -0.4 and have an apparent separation from the Sun of 21 degrees. However, because of the low angle of the ecliptic it will be only 8 degrees above the horizon at dawn. On 16th it moves into Scorpio and into Ophiuchus on 21st, when it rises at 06.31 and reaches 7 degrees in the east before the sky brightens.  After greatest western elongation it appears to move closer to Jupiter - on 21st and 22nd they are less than 1 degree apart.  On 31st it rises at 07.10 and is only 3 degrees above the eastern horizon at dawn.
PLEASE REMEMBER:  Do not try to look at Mercury - or any other celestial object - through a scope or binoculars when it is low in the pre-dawn sky. Even catching the frst few rays of sunlight is likely to cause permanent eye damage.

Venus:  in Virgo, mag -4.7
At its brightest at the start of December, totally unmissable for those who can bear to leave their nice warm beds before sunrise. On 1st it rises at 04.07 and reaches 22 degrees in the east as the sky brightens at around 7.30.  On this morning the 17% lit Moon passes close to the planet.  It begins to fade very slightly after the first few days, -4.6 on 4th, but a little higher at 23 degrees by dawn.  It moves into Libra on 14th when it rises at 03.59.  On Christmas morning it will be a very bright star in the east, rising at 04.06 and easily visible from around 5am, when all those with young children will, no doubt, have been awakened  At month end it will rise at 04.12 and reach 20 degrees by dawn, still blazing away at mag -4.5.

Mars:  in Aquarius, mag 0.00
An evening object in December, visible from around 16.30 and setting about half an hour before midnight. Still easy to see despite it fading as it is still getting higher in the sky.  On 1st it culminates at 18.11, a few minutes after the start of astronomical darkness, at an altitude of 27 degrees.  On the evenings of 6th and 7th it passes less than one degree north of Neptune. Moves into Pisces on 22nd, when it culminates at 17.30, reaching 33 degrees in the south. By month end it culminates a few minutes earlier and a couple of degrees higher but will have faded to mag 0.4.

Jupiter: in Scorpio, mag -1.7
A morning object, not easily seen especially in early December, as it is very low in the pre-dawn sky.  On 1st it rises less than half an hour before the Sun and appears only 3 degrees from it. Its position improves during the month, on 7th it is only one degree above the horizon as the sky brightens, on 14th,when it moves into Ophiuchus, it reaches 4 degrees. By 25th it might be visible from a site with a low, clear south eastern horizon, at an altitude of 7 degrees at around 08.00.  By 31st it is slightly brighter at mag -1.8 and a little higher,  9 degrees in the SE at 07.35.

Saturn: in Sagittarius, mag 0.5
Very low in the evening sky, on 1st it is only 6 degrees above the horizon at dusk, setting at 17.47.  Not likely to be visible after the first few days of the month, by 18th it is on the horizon as the sky darkens and on 31st sets only a few minutes after the Sun.

Uranus: in Aries, mag 5.7
Still very well positioned for binocular observation, especially in the earlier part of December. It is also relatively bright - for Uranus - so it's a good time to try to spot it with the naked eye from a dark sky site.  On 1st it culminates at 21 14, reaching 48 degrees above the southern horizon, setting at 04.21.  Its apparent motion is currently retrograde (east to west)  and it moves back into Pisces on 4th. By month end it reaches its highest point, slightly lower at 46 degrees, at 19.14 in astronomical twilight.  A reasonable sized amateur scope should show the planet as a small blue/green disc.

Neptune:  in Aquarius, mag 7.9
An early evening object.  On 1st it reaches 28 degrees in the south at 18.27, during astronomical darkness. By month end it culminates at 16.30,  an hour and a half before it gets fully dark.  Still a good amateur telescopic target during the early evening, though a much larger scope is needed to show any markings on the blue disc.

Dwarf Planets

Ceres: in Virgo, mag 8.8
Should be visible in amateur scopes, especially in the latter part of December. On 1st it rises at 04.39 and only reaches 13 degrees by dawn.   On 5th it moves into Libra and is slightly fainter at mag 8.9.  It is about 3 degrees to the north of Venus on the morning of 29th and on 31st rises at 04.39, reaching 19 degrees before the sky brightens.

The other dwarf planets are so faint that they are only targets for experienced astrophotographers.

Pluto, In Sagittarius, mag 14.7
Not a good time for trying to catch this - it never gets higher than 14 degrees above the horizon during darkness.  By month end its apparent distance from the Sun is only 11 degrees.

Eris:  in Cetus, mag 18.8. 
Much fainter but might be a better bet. On 1st it reaches 34 degrees in the south soon after 21.00, on 31st culminates at 19.10.

Haumea in Bootes, mag 17.4
On 1st it reaches 35 degrees by dawn, and by 31st is at 50 degrees as the sky begins to brighten.

Makemake: in Coma Berenices mag 17.2
Should be visible in the early hours, on 1st it reaches 51 degrees by dawn, on 31st culminates at 60 degrees soon after the end of astro darkness at 06.38.

For more details and exact positions of all planets, asteroids and comets see:

Meteor Showers

One major shower this month.

Geminids:  active 4th to 19th. Some sources give the peak night as 13th/14th others say 14th/15th.  Actual peak, according to the IMO, is 12.30 on 14th with near maximum rates for several hours either side of this, so either night is likely to be a good time to look.  ZHR under ideal conditions (dark sky, high radiant, no moon) is 150, so we might see as many as 50 from a reasonable site, probably no more than 20 per hour from Manchester. They are bright, often coloured, medium slow paced meteors which don't usually leave trails. Unlike most other showers these originate from an asteroid, 3200 Phaeton, rather than a comet.   The just past first quarter Moon won't interfere much, this year, setting at 21.57 on 13th and 23.04 on 14th.

Minor showers

Monocerotids:  Nov 27th to Dec 17th, peak 9th, ZHR 3
Weak, medium paced shower. 

Alpha Hydrids:  active 3rd to 15th, peak 12th, ZHR 3
Mostly very faint but the shower does often include some brighter meteors which could be confused with Geminids.

Coma Berenicids  12th to 23rd, peak 16th. ZHR 3
Another weak shower, best seen around 1am when the radiant is high.  These were once thought to be part of the Leo Minorids but are now considered to be a separate shower.

Leo Minorids: Dec 5th to Feb 4th, peak 20th, ZHR 5
A very weak but long lasting shower.

Ursids:  Dec 17th to 26th, peak 21st/22nd, ZHR 5-10 but there are very occasional short outbursts of up to 50.  These medium paced meteors originate from debris left by comet 8P/Tuttle.  The almost full Moon, above the horizon all night, will seriously interfere.

Comets

One (probably - fingers crossed) naked eye comet.

46P/Wirtanen starts the month very low down in Cetus at mag 6.1.  On 1st it culminates at 21.47 but is only 14 degrees above the southern horizon. However it should brighten quite rapidly during the first half of December, unfortunately not reaching the spectacular brightness originally predicted but probably getting to around mag 4.8 between 15th and 19th. It is also moving quickly northwards through Taurus (14th to 18th) Perseus (19th -21st), Auriga (22nd -28th) then into Lynx. On the night of 16th, when it is at perihelion, it passes between the Pleiades and the Hyades (the V shaped head of the bull) and should be quite high in the sky for most of the night.  It is at its closest to Earth on 18th when it passes about 6 degrees to the east of the California nebula (NGC1499).  Sadly, the almost full Moon wll spoil the view on that night. It becomes circumpolar on 21st and  on the night of 23rd/24th passes less than one degree from the bright star Capella.   It fades during the later part of the month, on 31st is predicted to be down to mag 6 but almost overhead - 84 degrees above the northern horizon at 00 25.
Even now, estimates of its brightness vary, some sources say that it will only reach mag 5.5 at its brightest. Even when it is at a theoretical naked eye magnitude it will still be difficult to see without optical aid.  The head and coma are quite large and diffuse, so it will appear as a faint fuzzy blob rather than a star like point of light.

Comet 46p/Wirtanen during December 2018
   

38P/Stephan-Oterma starts the month in Cancer at a mag of around 9.8.  On 1st it reaches its highest point, 65 degrees in the south, at 03.39 and should be visible in a small scope and be an excellent subject for keen astrophotographers. On 12th it moves into Lynx and is slightly higher, 69 degrees at 03.10. It's at its closest to Earth on 17th and on 19th becomes circumpolar, reaching 72 degrees in the south at 02.45.  Towards the end of the month it is caught up by the much faster moving Wirtanen, on 31st they are fairly close with Wirtanen about 30 degrees to the west.

 
There isn't a great deal of information on newly discovered comet C/2018 V1(Machholz-Fujikawa-Iwamoto)- and what I could find often differs.  What all sites agree on is that it is very low in the sky and unlikely to be visible.  Starts the month in Ophiuchus, setting around 18.00 on 1st.  On this day it is very close to the globular cluster M10, mag probably around 9. It moves into Sagittarius on 31st, when it is very close to Pluto - but the pair also appear very close to the Sun, too low in the bright evening sky to be seen, setting only an hour after Sunset.
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