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Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,


This month ushers in Midwinter for those in the northern hemisphere - and Midsummer for those readers in the Earth's southern climes. The Sun reaches the most southerly part of the ecliptic in the sky on 21st December 2017.  At this point of the year for readers around the 51 degree N latitude, the Sun will be just 15 degrees above the horizon at the highest point of transit in the south.  The more northerly you are, the less the Sun's altitude at transit point will be.  For those at the Arctic Circle the Sun won't rise at all.  Those above the Arctic Circle will be already experiencing total darkness for days or even weeks surrounding the Winter Solstice. No matter where you are in the northern hemisphere, this day will be the shortest of the year and the night the longest.  This is caused by the Earth's 23.5 degree polar inclination from its orbital plane - the major cause of the seasonal nature of our planet's weather.


The Earth at the Winter Solstice.  Image Credit: Kerin Smith

Conversely, those in the southern hemisphere will experience the longest day of the year, the shortest night and the very height of Summer on the 21st December.  Wherever you find yourself at this time of the year, we wish all you the very best, whatever season you're experiencing.  As usual, if you turn your eyes and telescopes skyward, there's lots to see…


The Solar System

The Moon

The Moon begins December at Waxing Gibbous phase, around 84% illuminated, in the zodiacal constellation of Pisces, the Whale. It reaches Full on December 3rd, high in sky (from a Northern Hemisphere perspective) in Taurus, rising around 4.20 in the evening (from latitude 51 degrees N), and setting a little before seven the following morning. This means inevitably, the first few days of December are not so great for deep sky observations or imaging with anything less than very narrowband filtration. 


While the Moon is Full it makes one of its regular jaunts through the Hyades star cluster, the head of the Bull, which Taurus represents. This area of sky sets for those in Europe and Africa while the event is taking place, making it impossible to witness Aldebaran, Alpha Tauri, being occulted by the Full Moon. Sadly, geometry doesn't even allow those further west in the Americas to easily observe the event, as the Sun will have risen before it occurs. It’s certainly not impossible to observe a daylight occultation with a bright star like Aldebaran telescopically, though.  However, it’s always worth wounding a note of solar caution when doing so - happily in this case for any daytime occultation-watchers out there, the Sun is very well separated from the Moon is the sky at this time.


The Moon reaches Last Quarter on the 10th, on the Leo/Virgo borders. 


On the morning of the 14th, before dawn, the thin old crescent Moon, some 13% illuminated, can be found between Mars and Jupiter, low in the SE, before the Sun rises.


Moon, Mars, Jupiter - predawn, December 14th. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

The Moon becomes New on December 18th, when it joins the Sun on the Ophiuchus/Sagittarius borders. After this point in the month, the Moon becomes an evening object, low in the southerly part of the ecliptic from the northern hemisphere. 


The Moon continues its evening journey through the ecliptic, providing a useful signpost for the planet Neptune in Aquarius on Christmas Eve - sitting about 2 1/2 degrees south of the planet. 


The Moon reaches First Quarter phase in Cetus on the 26th, sitting a little of 5 degrees to the south of Uranus the following evening, again, providing a useful guide to the location of the fainter planet in the sky. 


The Moon ends the year in spectacular fashion in Taurus - at 93% illuminated Waxing Gibbous phase - as it occults both the Hyades and Aldebaran, Alpha Tauri, a little after midnight on December 31st. This event will be well-placed for European observers , with the Moon still fairly high in the sky as it occurs. If the sky is clear, don't miss it. 


 Aldebaran emerging from Lunar Occultation, December 31st. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

The Planets




The Innermost planet begins the month as a relatively bright +0.1 mag, 37% illuminated evening target in Sagittarius. Although very well separated from the Sun (by just under 29 1/2 degrees), having recently reached maximum eastern elongation in late November, Mercury is still very low in the sky to sunset from the temperate northern hemisphere, so it's going to be a reasonably difficult spot in the dusk, sitting just under 5 3/4 degrees high as the sun goes down (from 51 degrees N).


Mercury is heading back towards the Sun, which it reaches as an inferior conjunction on December 12th. Before then, the planet appears to rise slightly in the sky, forming a reasonably close conjunction with Saturn on the 6th and 7th, before rapidly diving towards the Sun, losing brightness significantly as this occurs. This is due to Mercury drawing between us and the Sun, shortening its phase as it does so. While Mercury is getting closer to us, it certainly isn't getting brighter. Mercury passes to the north of the Sun in Ophiuchus on the 12th/13th and re-emerges as a morning object after this, though will be far too faint and close to the Sun for observation until the latter part of December. 


By the 22nd, we find Mercury a +0.5 mag, 28% illuminated target, sitting at just below 11 degrees in altitude at sunrise (from 51 degrees N) a resident of the western half of Ophiuchus. As the month progresses, the planet gets higher in the sky and brighter as it does. Mercury ends December at mag -0.3, still in Ophiuchus, at 60% illuminated Gibbous phase as the year ends. If you can brace yourself against the winter chill of an early northern hemisphere December morning, this is a great time to catch this illusive world. 


Mercury at Sunrise, 3st December. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,



Venus, at -3.9 on the 1st, is bright enough to be still an easy object to catch in the morning sky, though it is becoming painfully low in the dawn sky for those in the temperate northern hemisphere. At 98.7% illumination, our neighbouring planet sits just under 6 degrees high at sunrise (from 51 degrees N).  Venus and the Sun are separated by about 9 1/2 degrees on the 1st. 


By mid-month, Venus has dipped to under 3 degrees in altitude at sunrise (from 51 degrees N), but hasn't decreased in brightness, remaining much the same as it was at the beginning of the month. 


However, the trend as far as Venus is concerned continues to be downward, as the planet slips towards the Sun and superior conjunction in early January. By the time December is at its end, Venus hasn't changed in brightness, but is now pretty much unobservable as it swings around to the opposite side of the Sun to us here on Earth.  By December 31st, Venus and the Sun are separated by just over 2 degrees and the planet's time as a morning object is at an end - for now, at least. 


Inner Solar System, 31st December. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,



Mars starts December as a morning target in Virgo. At +1.7 mag and 4.2 arc seconds diameter. It is not a particularly inspiring object to observe at the present time. Mars' proximity to the Sun, just over 44 degrees on the 1st, doesn't make it especially hard to find, especially with the brighter star Spica, Alpha Virginis, to the SW nearby, but once located, the planet's small disk and comparatively low magnitude make for a rather disappointing experience at the telescope. 


We on Earth are slowly catching up with Mars on our faster interior orbit, but this is a rather drawn-out process. Opposition with Mars - our next closest approach to the planet - won't be until the end of July 2018. We still have some way to go before the Red Planet starts being a truly rewarding experience to observe. 


By the middle of the month, nothing has changed much as far as Mars is concerned. The planet's brightness has increased to +1.6 mag and its angular diameter is now 4.5 arc seconds across. 


By December's end, Mars stands just over 23 degrees high at sunrise (from 51 degrees N), a reasonably significant drop in altitude from the 28 degrees high it stood at the month's beginning. This is an inevitable factor of the Sun dropping into the extreme south of the ecliptic at this time of year. 


Mars is now at +1.5 mag and presents a 4.8 arc second diameter disk as the year ends.  Mars ends 2017 in reasonably close proximity to its planetary neighbour, Jupiter, in the sky, the two worlds separated by about 3 degrees. They will get significantly closer in conjunction in early January 2018. 


Mars and Jupiter, near transit point, dawn, December 31st. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,




Jupiter begins December as a -1.7 mag, 30.4 arc second diameter target in Libra. Standing about 18 1/2 degrees high at sunrise (from 51 degrees N), the planet will be easy to spot in the dawn sky. 


Jupiter - with Io and Great Red Spot Transit, early evening, December 5th. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

By mid-December, nothing much has changed as far as Jupiter's concerned: it is still -1.7 mag, has increased its diameter marginally to 32 arc seconds and now sits 21 3/4 degrees high in the east at dawn. 


Jupiter ends December 2017 having brightened fractionally to -1.8 mag and is now 33 arc seconds diameter. The planet stands 22 3/4 degrees high (from 51 degrees N) at sunrise, just next to Mars and a few degrees east of the meridian. 





While Saturn is observable for a brief window in early December, the Ringed Planet is rapidly dipping Sunward and reaches superior conjunction (the opposite side of the Sun from Earth) on December 21st. 


After this point, Saturn will slowly start to rise in the morning sky, but it will be a while before it is back to its best.   Saturn ends 2017 in Sagittarius, separated from the Sun by just under 9 1/2 degrees. It stands about 4 1/2 degrees high at sunrise (from 51 degrees N) on the 31st, having risen around an hour and a half before the Sun. 


Saturn at Superior Conjunction, December 21st. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,


Uranus and Neptune 


During December, both Uranus and Neptune are favourably positioned for evening observations in Pisces and Aquarius respectively. 


Uranus, ever the brighter and easier of the two at +5.7 mag and 3.7 arc seconds across, lies in the central "V" of the stars of Pisces, mankind the planet reasonably easy to find from a dark location. The Moon provides a handy guide to Uranus' position on the evening of the 27th, when both objects transit together at almost the same time from a European and African observational perspective. The Moon will sit around 5 1/4 degrees to the south of Uranus as this occurs. 


Uranus and Neptune, early evening, December 15th. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

On the evening of the 24th December, the Moon can also be used as a useful signpost to the location of Neptune. On this evening, the Moon sits to the south of Neptune by 2 1/2 degrees, with both objects transiting at just after sunset from a European perspective. As long as there isn't too much light scattered from the Moon, Neptune’s location should be fairly easy to identify using this method. 


With Neptune at +7.9 mag and 2.3 arc seconds in diameter, it is a great deal fainter than Uranus and will need a reasonable pair of binoculars in order to make a positive identification. Higher power telescopic views will show the planet as a noticeably blue colour disk, resembling a planetary nebula. Although a challenge to find without the use of a telescope with a goto mount, and accurate star charts, once found, Neptune is unmistakable. 





Comet C/2017 O1 (ASASSN)  continues to be well placed for observation during December. We begin the month with the comet hanging a few degrees from the pole star, Polaris, within the constellation of Cepheus.  The comet may have approached the limits of naked eye visibility (from a very good location), during the latter part of October - but is likely to have faded by a reasonably large amount from its peak by this point in time. However, most recent observations (at time of writing), put the comet towards the upper range of brightness estimates, so who knows what will occur? At worst, C/2017 O1 should still be a binocular object and worth looking out for. 


By the end of 2017, C/2017 O1 still sits in northern Cepheus but begins somewhat of a reversal in apparent direction, when compared to the stellar background stars. The comet continues back in the rough direction of its initial track through Cepheus as the first few weeks of the new year progress. 


Path of Comet ASASSN, December 2017. Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,



Arguably the best meteor shower of the year, the Geminids, peaks around the 14th December this year, with a ZHR of around 120 meteors, many (though not all) of which can be easily observed from a suitable given location.  This is a reliable shower, fed by the ancient "rock comet" Phaeton - a mysterious object with a 1.4 year orbital period, which is rather elliptical in nature. Is Phaeton a dead comet, or just a very dusty and rocky one? At the present time we are unsure, but this curious hybrid body's stream

of debris produces a reliably spectacular show. Equally curiously, unlike other major showers, such as the Perseids and Leonids, which have been recorded back in antiquity, the first records of the Geminids occurs in the early part of the 19th Century. 


A Geminid zips through Auriga and Taurus.  Image Credit: Kerin Smith

This year, the perennial menace of all meteor showers, the Moon, is around New as the shower peaks, so it's potentially negative influence won't be felt - or seen. If the weather is kind, conditions for watching or photographing the Geminids will be ideal. Naturally, as this shower peaks in mid-December, those in the northern hemisphere are encouraged to wrap up warmly before sitting or standing out in the cold for too long. A DSLR camera with a widefield lens or USB imager with an "All Sky" super wide C-mount lens will be ideal to record the event. 


Deep Sky Delights in Auriga and Taurus


Taurus and Auriga - Image created with SkySafari for Mac OS X, ©2010-2012 by Southern Stars,

The zodiacal constellation of Taurus, The Bull, is home to some of the most outstanding deep sky objects in the sky, the most notable of these is perhaps M45, the Pleiades, or the Seven Sisters.  At collective magnitude of +1.5, M45 is easily seen with the naked eye and has been recorded by numerous cultures throughout the world.  The ancients knew the Pleiades by different names: Subaru in Japanese, Krittika in Hindi, Soraya in Persian amongst many others.  The Pleiades are mentioned in Homer's Odyssey and Iliad, the Bible and the Quran.  It is known that cultures as far apart as the Maori and Aborigines and the Native Plains Tribes of North America had knowledge of this star cluster - which makes it pretty well-known worldwide!


M45 presents its nine major members, (named after siblings from classical Greek mythology), the "sister" stars of Merope, Sterope, Electra, Maia, Tygeta, Celaeno and Alcyone - along with the "parent" stars Altas and Pleione - to the naked eye from a very dark location, but most people with reasonable eyesight can split six under average skies.  Telescopes and binoculars reveal many more of the 1000-or so members of the cluster and larger instruments and photography can pick up blue-hued reflection nebulosity surrounding the cluster - particularly around Maia and Merope.  This nebulosity is caused by illumination of left-over material from the cluster's formation.  The view of M45 with a widefield, low power eyepiece is one of the most glorious sights in any telescope, though at 2 degrees in diameter, one has to be careful about eyepiece choice in order to get the outlying members in a useable field of view.


M45, The Pleiades Cluster.  Image Credit: Kerin Smith

The Pleiades are thought to be around 100 million years old and lie between 430 and 440 light years away.

Next door - though not cosmically speaking - to the Pleiades is the older and more spread-out Hyades cluster.  Its major naked eye members are arranged in a V-shape which marks the head of Taurus.  Again, similarly to M45, the Hyades have been known since antiquity and were traditionally seen by the Ancient Greeks as being the sisters of the Pleiades - via their shared father Atlas.


The Pleiades and the distinct "V" of the Hyades below (with Geminid Meteor).  Image Credit: Kerin Smith

The Hyades lie 152 light years away, and as such are nearest star cluster to us on Earth (though arguably the stars in the Plough or Big Dipper in Ursa Major can actually be thought of as a cluster and are closer).  The Hyades consist of over 300 individual stars and modern estimates put its age at around the 600+ million year mark - making it markedly older than the Pleiades.  The Hyades share a galactic trajectory with M44, the Beehive in nearby Cancer, again suggesting a common origin point in space.  However, the Beehive appears to be slightly older at 600-730 million years.


Line of sight puts Taurus' principle Alpha star Aldebaran - the eye of the Bull - within the boundaries of the Hyades, though this Red Giant is unrelated and distinctly closer to us at 65 light years.   


Reaching East down the Southerly "horn" of the Bull, we come to the +3 mag star Zeta Tauri.  This star is a convenient location point for another jewel of the night sky - the Crab Nebula, M1 on Messier's List.


The Crab Nebula is the remnant of a star which went Supernova in the year 1054 (to us here on Earth).  This event was recorded throughout the world, from New Mexico to China.  It would have been a dazzling sight, peaking at -6 mag, brighter than the planet Venus and visible in daylight.  After it faded, the event receded from popular consciousness and it was nearly 700 years later, in 1731, that the object than would become known as the Crab was discovered by Astronomer John Bevis.  Messier rediscovered it when searching for the return of Halley's Comet 27 years later in 1758.  First thinking the object was a comet, it was the Crab that prompted Messier to compile his list, so other comet-hunters would not be confused by these static, cloud-like objects when searching the heavens.


Lord Rosse, observing the Crab with what was then the largest telescope in the world at his Birr Castle Observatory in Ireland, in 1844, made a sketch that showed claw-like protrusions - presumably the filament structure of the outer lying regions.  The object was nicknamed the Crab - and the moniker stuck.


Early both Century photographic observations of M1 showed that the object was expanding rapidly.  This expansion was extrapolated backwards and it was noted that the object should have started its expansion around 900 years previously.  A little bit of astronomical detective work ensued and the events of 1054 and the Crab were tied together.


Although a hardly dazzling +8.39 mag, the Crab's is quite well condensed and as such its surface brightness is fairly high.  It can be found as a misty patch with ordinary binoculars, though larger binoculars reveal it as a definite elongated, round-edged feature.  Telescopically, the texture of the Crab becomes evident in refractors of 4-inches aperture or reflectors of the 6-8-inch class.  Reflectors of 16+ inches in aperture and dark skies are needed to glimpse the filament structures of M1's outlying regions and real striation in its core.  Filtration will help with this object, especially in small instruments where it can sometimes be difficult to isolate the nebulosity of the object from the rich background of the Milky Way.


Photographically, the Crab Nebula is a rewarding target, with the "Hubble Palette" of H-Alpha, OIII and SII being particularly useful in bringing out the tangled, chaotic structure of the object's core.  Though it can be very effectively recorded with single shot colour cameras, as displayed by Mark Blundel's picture below, which was taken with a Canon 1100D via a Meade 6000 Series Triplet Refractor on a Skywatcher HEQ5 Pro mount, guided via the Orion Magnificent Mini Autoguider package.


The Crab Nebula.  Image Credit: Mark Blundell

No-one with any form of optical equipment should ignore the Crab Nebula. While not as spectacular is the neighbouring Orion Nebula, it is the only easily-observed remnant of a Supernova that humans have actually observed in relatively recent history.  Given the dearth of Supernovae in our galaxy in recent times, the Crab remains a special object to us.


Moving northwards into Auriga, the Charioteer, following straight line from Zeta Tauri, the more southerly tip of the Bull's two horns, through Elnath, one of the few stars in the sky that is shared between two constellations, giving it the classification of both Beta Tauri and Gamma Aurigae, we come to the Flaming Star Nebula, IC405.  Found 6 degrees north of Elnaith, this object is a partial emission, partial reflection nebula, meaning that one  part of its structure glows under excitement from radiation, whereas the other part merely reflects light from the stars imbedded in the object.  Measuring around 30 x 19 arc minutes, IC405 is centred around the star AE Aurigae, a star which was ejected from the nearby Orion Nebula under 3 million years ago.  At +10 mag, it is not an intrinsically bright object, but condensed enough to be seen in small telescopes from a decent location.  It is unsure if any of the material that makes up the Flaming Star Nebula was once a part of the Orion Molecular Cloud - it is more likely that it is material that the star is merely passing through.  As previously mentioned, this is an area rife with gas and other star forming material.  IC405 lies some 1500 light years from Earth.


The Flaming Star Nebula.  Image Credit: Mark Blundell 

Just under 3 degrees to the NE of the Flaming Star lies the first of Auriga's three great open star clusters, the lovely M38, otherwise known as the Starfish Cluster.  It's difficult to see exactly what resemblance this +6.4 mag, 20 arc minute diameter collection of stars has to the titular marine invertebrate, but it is certainly a pretty sight in any sort of optical instrument.  M38 was first recorded by the preeminent Sicilian astronomer Giavanni Batista Hordierna in 1654 and re-squired much later by French observer Le Gentil in 1749.  Le Gentil's observations alerted Charles Messier to M36's location and it was included in his original list in 1764.


At over a third of a degree angular diameter, M38 is ripe for observation in most telescopes and binoculars.  Observers will note long chains of stars, many of which are blue, but there are also some lovely contrasting yellow and gold-coloured members.  In total, M38 has around 100 stars as members and lies around 4200 light years from us.  It is thought to be around 200-225 million years old.


M38 (bottom left).  Image Credit: Christos Doudoulakis, Creative Commons.

2 and 1/3 degrees to the SE of M38 we come to the second of Auriga's great clusters, M36.  This cluster is a good deal more compact than its neighbour at 10 arc minutes diameter and slightly brighter as a resultant +6 mag.  Through a telescope, this collection of hot white stars can appear quite brilliant in comparison to M38 - indeed, it is said that if M36 were placed in the position of the Pleiades, it would outshine them by a factor of three.  M36 was again discovered by Hordierna, in 1654, rediscovered by Le Gentil and added to the Messier list in 1764.  


M36.  Image Credit: Ole Neilsen, Creative Commons.

This cluster is a good deal younger than its neighbour and contains many young hot blue main sequence stars, of spectral type B2 and B3.  There are no older population stars to speak of in M36, so it is thought to be just 25 million years old.  Lying at around 4300 light years hence, M36 is one of the many objects that share the moniker "The Pinwheel" - though apart from a circular collection of stars to the NE side of the cluster, it is difficult to see why it has picked up such a name - especially in the light of the other "Pinwheels" in the sky.  Perhaps we should come up with a new more original nickname for this great cluster - it deserves better.


The last of Auriga's fine open clusters is its best - the spectacular M37.  There are many great clusters in this area of sky: the much nearer Hyades, Pleiades, Beehive, the nearby M35 in Gemini and the Double Cluster in Perseus - but M37 is one the most beautiful of these and is a lovely sight is any telescope or binoculars.  At a quarter of a degree in diameter, M37 is about the same angular size as the Full Moon in the sky.  It is also the brightest of Auriga's "Trio" at +5.59 mag and the oldest at an estimated 300 million years of age.  Like its neighbours, M37 contains many hot blue stars, but also significantly many more mature yellow, orange and red giant stars.  This more evolved stellar population makes for some fine viewing for we astronomers here on Earth as the blues of the newer, hotter population contrast superbly with the warmer tones of the older stars.


M37. Image Credit: Ole Neilsen, Creative Commons.

M37 was again discovered by Hodierna, though almost inexplicably was missed by Le Gentil - Messier himself found it again at catalogued it in 1764.  M37's total stellar population is thought to number in the 500+ levels, of which maybe 150-or-so are observable in amateur telescopes.  It is the furthest lying of Auriga's clusters at 4500 light years distance and the largest at 25 light years across.


Sitting astride (from a northern hemispherical perspective) this rich are of sky is Auriga's principle star, Capella.  At +0.08 mag, Capella is the sixth brightest star in the night sky, being a shade fainter than Vega.  It is comprised of two large G-type stars - roughly the same temperature as our Sun - but these are much larger in mass and diameter and have already begun to exhaust their nuclear fuel.  Despite being a little over 42 light years away, this system is not split-able (as yet) with even the largest of Earth-bound telescopes, as the two main component stars orbit a common centre of gravity which keeps them around 60 million miles apart, roughly 2/3rds of the distance between the Earth and Sun.  There is a much fainter outlying star system which is gravitationally bound to the main Capella pairing, though this comprises itself of two faint M-class dwarf stars, making the whole system technically a Quadruple star.


Text: Kerin Smith