Night sky notes for December 2018 Geoff Mitchell
The December night sky now sees the late autumn constellations prominent early evening and now heralds some familiar winter constellations. The late autumn / winter night sky contains many fine objects to view with both binocular and small telescopes. Also this month a short period comet, Comet 46P Wirtanen reaches its closest point to the Sun in its orbit (Perihelion) on December 12th at a distance of 1.055 AU. The Comet has an orbital period of 5.43 years and on this occasion perihelion coincides with a close approach with the Earth, closest distance occurs on December 17th at a safe distance of 0.077 AU (11.5 million Km.).
Look to the east mid evening to see the seven sisters’ (Pleiades, M45) star cluster and constellation Taurus which heralds the autumn skies. The Hyades star cluster makes the characteristic `V` shaped asterism in the constellation of Taurus and is noted for the bright, red foreground star Aldebaren in Arabic Al Dabaran is `The follower ` of the Pleiades across the skies `, in old English colloquially known as `the eye of the bull`.
Comet 46P Wirtanen will be binocular / naked eye visible from darker sites on moonless evenings in mid December , changing its position (night to night) , passing within a binocular field of view of the Seven Sisters (M45) star cluster in Taurus around December 12th (See notes for Map) . At close approach the coma `apparent diameter ` will look larger than a Full Moon diameter and so the coma will resemble a tenuous round `fuzzy` cloud due to the low surface brightness. It is a good opportunity to take a photograph using a tripod mounted DSLR camera with remote trigger, 50mm lens, B setting exposure 10 sec to 20 sec, ISO (ASA) 1600 and capture the constellation of Taurus, the Hyades, Pleiades (M45) star clusters and the Comet.
The constellations of Cygnus and Lyra can be seen slipping into the west early evening; these are noted for the bright stars of Deneb and Vega. The Milky Way stretches from the constellation of Auriga , marked by the bright star Capella in the east up into Perseus and through the `W` shaped constellation of Cassiopeia high overhead and down along the cross shaped constellation of Cygnus low in the west . This faint band of stars best seen on dark moonless evenings
Auriga has the bright star Capella, which is circumpolar from UK latitudes and so is always visible. The constellation of Auriga contains some nice star fields and open star clusters visible in binoculars, notably M36, M37 and M38
High In the south the constellation of Pegasus, noted for its `Square ` shape and the adjacent constellation of Andromeda noted for The Andromeda Galaxy (M31) , visible to the unaided eye as a faint fuzzy patch on moonless evening can now be seen mid evening . The Square of Pegasus is a useful sign post constellation and also is a good test for sky conditions, (how many faint stars you see within the square is indicates just how good your seeing conditions are). Follow the two end stars (Scheat and Markab) down to find the star Fomalhaut in the constellation of Pisces Australis (The Southern Fishes), visible very low on the southern horizon early evening mid month. Another fine globular cluster is M15 in the constellation, best seen telescopically.
In the north Ursa Major or The Great Bear, known for The Plough asterism is seen low with its handle parallel to the horizon mid evening. Use the right hand pair of stars Dubhe and Merak (The pointers) to find the faint pole star Polaris currently marking a position close to the north celestial pole.( useful when polar aligning your equatorial telescope mount )
Uranus in the constellation of Pisces is visible early evening and can be located using binoculars and a suitable finder chart. A good starting point is to locate the Square of Pegasus and the ring of stars below the Square known as the `Circlet` in the constellation of Pisces (The Fishes), then star hop using the finder chart. Uranus is notable due to the blue colour, telescopes show a tiny disc rather than the sharp pinpoints of stars in the field of view.
By late evening the familiar winter constellations of Orion (The Hunter) with bright red star Betelgeuse (top left) , white star Rigel (bottom right ) and the three stars of Orion’s belt Mintaka , Alnilam and Alnitak . Below Orion’s belt can be seen the misty patch that is M42 / M43, visible to the unaided eye, it is one of the gem’s of the winter skies when seen with a telescope. This nebula some 30 light years across is illuminated by a group of four hot young stars that is known as the `Trapezium `asterism, visible under moderate magnification.
Planets in December 2018
Mercury is our morning twilight skies this month with greatest elongation on Dec 15th 2018.
Venus is well placed in dawn skies this month shining brightly at -4.5m, telescopes show 45% phase.
Mars is an evening object (+0.4m) due south at 7pm, close conjunction with Neptune Dec 6th /7th
Jupiter emerges into dawn skies during December, low in the east with Mercury and Venus
Saturn is lost to daylight in December reaching conjunction on Jan 2nd 2019
Uranus is an evening object in the constellation of Pisces; the planet shows a tiny blue disc telescopically.
Neptune is located due south with Mars in early December (Same telescope field of view as Mars Dec 6th/7th )
Moons phases in December 2018
New Moon Dec 7th Moonless, best time for deep sky and comet observing.
First Quarter Dec 15th Best days to see shadow details in lunar craters (early evening)
Full Moon Dec 22nd Best days to see bright ray craters like Copernicus / Tycho.
Last Quarter Dec 29th Moon visible in daytime skies. Do not look directly at the Sun.
Winter solstice Dec 21st (22:23 GMT) – Shortest day
Geminid range December 8th to 17th, maxima 14th December – ZHR 100 /hr slow, bright meteors favourable.
Ursid range December 17th to 25th maxima Dec 23rd – low rates ZHR just 10/ hour – unfavourable.
The highlights of the month.
Comet 46P Wirtanen early / mid December moves north in Taurus early evening Binocular /Naked eye
December skies, Milky Way visible high overhead on moonless evenings in darker skies.
M31 the Andromeda Galaxy is visible on moonless evenings, best seen in binoculars.
Double cluster, on the Perseus / Cassiopeia border, nice pair of star clusters.
Pleiades (Seven Sister’s) star cluster (M45) rising in the east best seen with binoculars.
Orion Nebula (M42) is a beautiful sight seen telescopically.
Crescent Moon visibility, a 1.9 % waxing crescent moon is visible in twilight in the south west from around 20 minutes after sunset (from 4.10 pm) with moonset by 5:03 pm on December 8th
More detailed sky notes and LAS Newsletters, Finder charts are available to LAS members via the Members` page on the LAS Website www.lutonastrolink.org.uk
Sky looking south 7pm in mid December
Follow the stars Scheat and Merkab in the square of Pegasus down to find the star Fomalhaut in the constellation of the `Southern Fishes ` Pisces Australis. Rare conjunction of Mars and Neptune puts the two planets in line of sight as seen from Earth, just 0.04° separation on the evenings of December 6th and 7th ie in the same telescopic field of view.
Position of Mars and Neptune early December (conjunction Dec 6th /7th 2018) Telescopic field of view (x95)
Sky looking east at 7pm mid December
The constellations of Taurus, Auriga, Gemini and Orion can be seen rising mid evening in December.
The path of Comet 46P Wirtanen is plotted the position shown for each date
The Seven Sister’s cluster (M45, Pleiades) is an easily identified star cluster. Some people with keen eyesight may see up to 13 stars, but a telescope will show over 200 faint stars in the cluster.
Sky looking north at 7pm mid December
Follow the pointer’s Dubhe and Merek to find the polestar Polaris
Sky looking west at 6pm mid December2017
The summer triangle asterism of Altair, Deneb and Vega slip westward
LAS general finder chart for Uranus for Nov / Dec 2018
Uranus now past opposition is around 5.7 magnitudes positioned in the south early evening, visible in binoculars or small telescope as a blue coloured star like point near Zeta Piscium. Use the Circlet or Square of Pegasus to star hop to the field of view. [Position RA 01h 32m, Dec +09° 57m.
General finder map Neptune RA 22h 53m , Dec -8° 2` , Mag 7.9 Neptune is close to Lambda Aquarii
Mars and Neptune are in close conjunction on the evening of Dec 6th / 7th 2018
Comet 46P Wirtanen
Binocular / Naked eye visible during moonless evenings in December 2018
- Comet moves steadily northward (night to night) passing close to the Seven Sisters cluster (M45) on the evening of December 16th. Positions shown for 20:00UT on the dates shown.