The night sky in December 2020

posted 29 Nov 2020, 08:36 by Pete Collins   [ updated 30 Nov 2020, 04:39 ]
by Anne Holt

Sunrise      1st:    08.02       31st:    08.25
Sunset       1st:    15.53       31st:    15.59

Astronomical darkness
1st:  18.01 to 06.55           31st:  18.10 to 06.14

Shortest day:  21st at  7hr  28'  27".  
This day is also the winter solstice, when the Sun reaches its most southerly point in the sky.  It is overhead at local noon along the Tropic of Capricorn.
In the southern hemisphere it's the summer solstice.

Latest sunrise:  08.25  from 28th to 31st. 
Earliest sunset:  15.49 from 9th to 17th.

Earliest astro darkness start:  18.00  from 4th to 16th.  
Latest astro darkness end:      06.14 from 28th to Jan 6th.

New Moon:  14th at 16.16     Full Moon:  30th at 03.28
There is a total solar eclipse on 14th but it is only visible from parts of Chile and Argentina.

Lunar perigee:   12th at 20.43   (361776 km)
Lunar Apogee:   24th at 16.33   (405009 km)

The December full Moon is known as the Cold Moon, for obvious reasons.
Other names are the Colonial American Christmas Moon, the Chinese Bitter Moon, the English Medieval Oak Moon, and the Neo Pagan Long Night Moon.  As always indigenous American tribes had various names, including the Cherokee Snow Moon and the Choctaw Peach Moon (maybe they thought it looked like a peach, I doubt they grew at that time). The Dakota Sioux, usually good for very descriptive names appear to have run out of ideas - either that or nothing much happened in December.  They called it the Twelfth Moon.
The Old English / Anglo Saxon name for December's full Moon is the Moon Before Yule.  No idea what they called it when, as this year, it fell after Christmas, right at the end of the Yule period.

Highlights

We have lots of astro darkness in December, nearly 13 hours on 1st and a few minutes over 12 hours at the end of the month. 
Mars is still high in the sky in the early part of the night, fainter now but still prominent as it is in an area of the sky with no really bright stars.  Venus is shining brightly in the morning sky early in December, but not getting very high before dawn breaks.  By the end of the month it will be difficult to see, only reaching 6 degrees as the sky brightens.   The 2 ice giants, Uranus and Neptune, are well placed for binocular and telescopic observation in the early part of the night. 
We have several minor meteor showers and one very major one, the Geminids, usually the best of the year, if the clouds stay away.
And, of course, there is the long awaited Great Conjunction of Jupiter and Saturn, they will be close but also very low in the evening sky, so only visible for a short time after sunset.  This won't be an exciting sight for the naked eye, as it will appear much as Jupiter usually does, however both planets, and maybe a few moons, in the same field of view of a telescope will be something really worth seeing.

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 -0.8
Not easy to see this month as it remains very low in the sky.  On 1st it rises at 07.00, an hour before the Sun, and only gets to 3 degrees above the horizon by dawn. On 4th, when it moves into Scorpio, that is down to 1 degree.  It moves into Ophiuchus on 9th and is at aphelion, at 0.49 AU, on 16th.  Even though it is now at its furthest from the Sun, it appears very close to it, only 2 degrees separation.  On 19th it goes into Sagittarius and the following day is at superior solar conjunction, passing about one and a half degrees to the south of the Sun. By 31st it is an evening object but still not visible, it sets only a few minutes after the Sun and appears separated from it by only 6 degrees.

Venus:  in Libra, mag -4.0
Now only visible for a short time in the morning sky.  On 1st it rises at 05.17 and reaches 15 degrees in the SE as the sky brightens around 07.30.  On 12th the thin crescent Moon passes only 47' from the planet at 21.07, they are separated by about 5 degrees soon after 06.00 on 13th, as the Moon rises.  Observers on the NE Pacific Ocean will see an occultation, those in parts of the west coast of the US and Canada should be able to see Venus disappear behind the Moon before they set.  It moves into Scorpio on 18th, when it rises at 06.13 and only gets to 9 degrees by dawn, on 22nd when it goes into Ophiuchus that is down to 8 degrees.  On 31st it rises at 06.50 and is only at 6 degrees when the sky brightens.

Mars:  in Pisces, mag -1.1.
Still high in the early evening sky, culminating in darkness throughout December. Despite being almost a magnitude fainter than Jupiter, it looks as bright in the early evening as it is higher and further east, so is seen in a darker part of the sky.  On 1st it reaches 43 degrees in the south at 20.27 and should be visible until around 2am, when it drops to 8 degrees in the west, setting at 03.10. On 23rd the 68% Moon passes just over 5 degrees to the south at 23.24, four hours after the planet has culminated.  On this day it should be visible till around 01.20, setting at 02.25.  On 31st it culminates, 47 degrees in the south, at 19.05 and is down to 9 degrees in the west soon after 1am, setting at 02.14 now at mag -0.3.

Jupiter and Saturn: in Sagittarius, mags -2.0 and 0.6 respectively.
Moving closer together quite quickly as they approach conjunction. On 1st they are separated by 2 degrees 15' at 16.30.  Jupiter should be visible from 16.15, at 14 degrees in the south, Saturn, because it is so much fainter, probably won't be seen for another half hour, when it will be at 13 degrees. Jupiter sets at 19.14, Saturn at 19.28.  On 16th Saturn moves into Capricorn and the following morning the waxing crescent Moon passes just under 3 degrees south of the planets at 05.12, while they are all below the horizon. It is quite close to the pair on the evenings of 16th, when it is about 7 degrees to the right, and 17th when it is to their left.   On 19th, when Jupiter follows Saturn over the border into Capricorn, the separation between the two is around 15' (that's half the width of the ful Moon).  On this day Jupiter sets at 18.25, Saturn at 18.27.  Two days later, as the sky fades around 16.20, the pair will be separated by only 6' - the closest since 16th July 1623. On this occasion they were only a few degrees from the Sun so wouldn't have been visible.  The last easily seen Great Conjunction was on 4th March 1226.   On 21st, Jupiter should be easy to see despite its low altitude - only 11 degrees - the much fainter Saturn just above it, less so.  The two will easily fit into the same field of view of a pair of binoculars or an amateur scope.
Jupiter sets at 18.18, Saturn very soon after.
The usual warning:  DO NOT use binoculars or a scope to look at the pair until you are sure that the Sun has fully set. Catching just a few rays could result in instant, permanent blindness.
Sunset in Manchester on this day is at 15.51. Check local times if observing from elsewhere.
Of course, it's quite likely that the sky will be cloudy on 21st so, if there are any clear evenings in the week before or after that date, it's worth looking, as the two planets will be close enough to be seen together in a scope at a magnification of around x40 during that time.  They will be less than 1 degree apart from 13th to 30th, less than half a degree from 18th to 26th. Obviously the days before 21st are preferable, as the pair will be even lower in the sky towards the end of the month. On 31st the separation is just over one degree but Jupiter will be visible for only a very short time in the twilight, 9 degrees above the horizon around 16.30, setting at 17.52. Saturn will be too faint to see in the still quite bright sky, setting at 17.47.

Uranus:  in Aries, mag 5.7
Now rising in daylight but still high enough for observing for much of the night. On 1st it is at 25 degrees in the east as the sky darkens around 17.30. It culminates, 30 degrees in the south, at 21.45 and will remain high enough for observing until after 02.30. On the night of 24th/25th the gibbous Moon passes close to the planet, about 4 degrees to the WSW at midnight. This is a good time to try to spot it through binoculars or even with the naked eye if you're lucky enough to be in a dark sky area.  You never know, while you're out there observing you might even spot Santa on his rounds. On 31st it should become visible, 41 degrees in the SE, soon after 17.30, culminating 8 degrees higher at 19.44.  It will be down to 21 degrees in the west by 00.35, setting at 03.07.

Neptune:  in Aquarius, mag 7.9
Also rising in daylight.  On 1st it is 28 degrees in the SE at 17.25, culminating at 18.42 when it is a couple of degrees higher. It remains reasonably high until almost 21.30.  On 20th at 20.00 the 32% lit Moon passes 5 degrees SW of the planet, which at this time is at 22 degrees in the SW.  On 31st it will be at 30 degrees in the south as it becomes visible around 17.30, having culminated in twilight at 16.46.  It will be high enough for telescopic or binocular (for those with dark skies) observation for a couple of hours, setting at 22.15.

Dwarf Planets

Ceres: in Aquarius, mag 9.2
In the same region of the sky as Neptune, but considerably lower and fainter, so difficult to see, even with optical aid.  On 1st it culminates at 18.04 as astro darkness begins, but is only 16 degrees above the southern horizon.  By 31st, now down to mag 9.4, it culminates half an hour after sunset and sets at 21.09.

Pluto:  in Sagittarius, mag 15.1
Jupiter and Saturn are now moving away from the very much fainter dwarf planet. On 1st it is very low in the SW as the sky darkens - much too low for successful imaging, and its position gets even worse as the month progresses.  By 31st it appears only 14 degrees from the Sun.

Haumea:  in Bootes, mag 17.4
An early evening target for keen astrophotographers. On 1st it rises at 02.11 and reaches 34 degrees in the SE before the sky gets too bright.  On 31st it rises at 00.26 and gets to 40 degrees in darkness, still not quite culminating before dawn.

Makemake:  in Coma Berenices, mag 17.2
High enough in the morning sky for imaging.  On 1st it rises at 00.21 and is 49 degrees in the east at dawn.  On 31st it rises at 00.21 and reaches 21 degrees in the east soon after 1am, culminating at 58 degrees half an hour after the end of astro darkness.

Eris:  in Cetus, mag 18.8
A target for only the most experienced astrophotographers as it is so faint.  On 1st it is almost 20 magnitudes fainter than Mars.  At a difference of 100x for 5 magnitudes this means that the difference between the two is 100x100x100x100, so Eris is 100 million times fainter than Mars!  The good news is that it's quite high in the sky in the early part of the night, reaching 34 degrees by 21.00 on 1st and the same altitude at 19.11 on 31st.

Comets

Once again nothing spectacular is predicted.  There are a few comets around but they are quite low or very faint.  As always, comet brightness is difficult to predict so the figures given could prove to be wrong - in either direction.

C/2020 S3 (Erasmus)
Discovered on Sept 17th by Nicolas Erasmus, while working on the ATLAS sky survey. It is expected to reach binocular brightness in the early morning sky.  However it is very low and getting lower as the month progresses. On 1st, in Libra, at predicted mag 6.8 it rises at 06.20 but only reaches 12 degrees before dawn.  It brightens over the next 3 weeks but gets lower in the sky as its apparent distance from the Sun decreases.  It moves into Scorpio on 9th, when it rises at 07.04, now at mag 5.9 but separated from the Sun by only 16 degrees. This is down to 12 degrees on 13th when it crosses into Ophiuchus.  On 22nd it goes into Sagittarius, rising at 07.40 in civil twilight and only 5 degrees from the Sun. It is now down to mag 6.9.  On 31st it rises 40 minutes before the Sun and sets 50 minutes after it but still appears very close - separation 7 degrees.  Mag now predicted to be down to 8.3.

C/2020 M3 (ATLAS)   (not to be confused with C/2019 N1 (ATLAS) which is too low to be seen from the UK.)
in Taurus, mag 9.4
This one gets higher during the month but fades rapidly. On 1st it is reasonably high for most of the night, culminating at 00.59 when it is 61 degrees above the southern horizon. On 4th it moves into Auriga and culminates at 00.40, now at 66 degrees.  It is circumpolar from 17th but much fainter, predicted mag now 10.4.  On 31st it gets to 81 degrees in the south at 22.40 but will have faded to mag 12.1.

88P/Howell: in Capricorn, mag 10.2
An evening object, fading as it gets higher in the sky.  On 1st it is at 14 degrees in the SW as the sky darkens, setting at 19.59. It moves into Aquarius on 27th and on 31st, down to mag 11.3, is 18 degrees above the horizon at dusk, setting at 20.24.

141P/Machholz:  in Aquila, mag 10.8
Might be visible through a scope for a short time as the sky fades.  On 1st it will be at 22 degrees in the SW at 17.30, setting at 20.40.  During the month it should brighten slightly and get higher in the evening sky. It moves into Capricorn on 2nd, Aquarius on 9th and back into Capricorn on 19th when it will be at 23 degrees in the SW at dusk, now at mag 9.7.  It is back in Aquarius from 25th, when it is 24 degrees in the SW as the sky darkens.  On 31st it is a degree higher at dusk but now fading again, down to mag 9.8,and setting at 21.23.

Recommended websites for more information and exact positions of all solar system objects
https://in-the-sky.org  (this is my favourite, most of the information here derives from this site)

www.cometwatch.co.uk  (often not updated for months.  The current observable comets page was done on Nov 11th, the rest not for quite some time)

Meteor Showers

This month we have what is generally regarded as the best, most reliable shower of the year.  It's definitely worth piling on all the thermals and venturing outside if the sky is clear.

Geminids:  active 4th to 20th with a broad peak centred on the early hours of 14th. ZHR under ideal conditions is 150, much fewer from Manchester, of course, but could reach 100 from the darkest parts of the region. The best displays should be around 2am, when the radiant is highest, however it rises soon after sunset so there could be reasonable activity earlier in the evening.  They are slow moving meteors, often very bright especially round the peak time, and sometimes colourful, so are ideal photographic subjects.  Parent body is asteroid 3200 Phaeton.  The good news is that there won't be any Moon interference arond the peak time. Fingers crossed that the same is true for clouds.

Minor showers

December (phi) Cassiopeiids: active 1st to 8th,  peak 5th, ZHR variable.  The radiant of these is circumpolar, highest at 21.00, peak time given as 23.00.  This shower is not included in the IMO list, which probably means that there hasn't been much, if any, activity in recent years.

Monocerotids:  active 5th to 20th, peak activity predicted to be 22.00 on 8th but best seen around 2am, when the radiant is highest.  ZHR 2 or 3. These metors are often confused with Geminids as they have a similar velocity and appear to emanate from roughly the same part of the sky.

Sigma Hydrids:  active 3rd to 20th.  The IMO gives the peak as 9th, but says it could be several days later on 14th.  Other sources say 11th or 12th.  ZHR 7.  The shower is best seen around 3am, when the radiant is highest - but on which day is anyone's guess!  It often includes several very bright meteors, much faster moving than the Geminids and Monocerotids which are active at the same time.

Coma Berenecids: active 12th to 23rd, peak 16th, ZHR 3.  Once thought to be part of the Geminids but now considered to be a separate shower.  These are much faster moving, best seen just before dawn when the radiant is highest.

December Leonis Minorids:  active Dec 5th to Feb 4th, peak Dec 19th, ZHR 5.  This is a weak but long lasting shower.  A few meteors may be seen at any time during the peak night.
 
Ursids:  active 17th to 26th, paek 22nd, ZHR 10 (but occasionally up to 50). This shower of medium slow meteors had major outbursts in 1945 and 1986 and lesser ones in 2014 and 2015.  There could be enhanced activity this year on 22nd, between 03.00 and 22.00, especially at 05.27 and 06.10.  Rates for these outbursts are given as 420 and 490 but, as they are predicted to last for a very short time, this means only 7 or 8 in a minute.

There are a couple of showers only visible from the southern hemisphere.

Phoenicids:  active Nov 28th to Dec 4th,  peak 2nd, ZHR variable.  Very slow moving meteors.

Puppis Velids:  active Dec 1st to 15th, ZHR 10.  Medium speed.

And there is the possibility of a few meteors on Dec 4th at 05.55 - the 66 Daconids, very slow moving meteors originating from debris left by asteroid 2001 XQ.






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