Age: 27 days old
Phase: Waning Crescent
Distance: 386,711 km
Ian Morison tells us what we can see in the northern hemisphere night sky during December 2014.
During the later evening, the Great Square of Pegasus is setting towards the west, with the constellation of Andromeda above and to its left. The W-shape of Cassiopeia is higher still, with Perseus just below and the Perseus Double Cluster between them. Below Perseus is Auriga, containing the bright star Capella, while Orion the Hunter is rising in the south-east. The three stars of Orion's Belt point down to Sirius, the brightest night-time star. Taurus the Bull is between Orion and Perseus, hosting the open clusters of the Pleiades and Hyades, as well as the red star Aldebaran, which appears to be part of the Hyades but is actually just lying along the same line of sight from Earth. Gemini is to the left of Orion, with the stars of Castor and Pollux representing the Twins. Rising later are Cancer, home to the Beehive Cluster, and Leo, the current residence of the planet Jupiter.
- Jupiter rises around 22:00 UT (Universal Time) at the beginning of the month, shining at magnitude -2.2 and positioned some 10 degrees up and right of the star Regulus in Leo. It closes to 7 degrees from Regulus on the 9th, and then begins retrograde (westward) motion across the sky. Jupiter rises around 20:00 by month's end, and has a magnitude of -2.4. It reaches a maximum elevation of 53 degrees when due south, which is at about 05:00 at the start of December and two hours earlier at the end. Its disc grows from 40 to 43" during the month, making surface features visible in a telescope.
- Saturn passed behind the Sun last month, and rises an hour before the Sun at the beginning of December and three hours before it at the end. It is in Libra, above the star Antares in Scorpius, with a magnitude of +0.5. As it rises in the south-east, its ring system is visible through a telescope as it is now angled at 24 degrees to our line of sight.
- Mercury passes in front of the Sun on the 8th, rendering it invisible until the very end of the month, when it may just be spotted low in the south-west after sunset. It is then 3.5 degrees to the lower right of Venus, and binoculars may be needed to see it at magnitude -0.8.
- Mars moves from Sagittarius into Capricornus on the 4th. It dims from magnitude +1 to +1.1 during the month, and shrinks from 5.1 to 4.8". It is low in the south-west for around three hours after sunset, its elevation and apparent size making surface details very difficult to see.
- Venus is now an evening object, setting shortly after the Sun at the start of the month and just over an hour afterwards at the end. Shining at magnitude -3.9, it should be easily visible in the south-west in late December, but low elevation and small angular size of around 10" will make its disc appear fuzzy through the Earth's atmosphere - a spectrum of colours may even be seen as it twinkles.
- Jupiter is impressive this month, as it will be for the next few.
- Mars lies just 0.3 degrees from the globular cluster M75 on the evening of the 3rd, and is still less than a degree away the following night.
- The Geminid meteor shower is best seen after midnight UT on the 14th and 15th. The radiant, from which the meteors appear to originate, is in the constellation of Gemini, but a third-quarter Moon will wash out fainter meteors. Unusually, the dust that produces the Geminids comes from an asteroid rather than a comet.
- The Ursid meteor shower peaks around midnight UT on the night of the 22nd-23rd, with its radiant near to the star Kochab in the constellation of Ursa Minor. There may be around 10 meteors per hour, but, by coinciding with new Moon, the shower is easier to spot than in other years.
- The Alpine Valley is a nice lunar feature to observe on the 13th and 29th this month, when it is close to the shadow-line (terminator) separating the Moon's day and night sides. A cleft in the Apennine Mountain chain, it is 7 miles wide and 79 miles long and has a thin rill running along it. The craters Plato and Copernicus become visible over the two nights following the Alpine Valley's appearance.
- Ian highlights two pieces of freely available software that are good for making star trail images during the long nights this month: the image-stacking programme StarStaX and the photo-editing software Adobe Photoshop CS2.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2014.
The nights are at their shortest on the 22nd and the night sky is dominated by the constellations of Taurus, Orion, Canis Major and Canis Minor. In Greek mythology, Orion the Hunter is the enemy of Scorpius the Scorpion, and so the two appear on opposite sides of the sky. The figure of Orion appears upside-down to southern hemisphere observers. The line of three stars forming his Belt are historically known in Aotearoa (New Zealand) as Tautoru, and his Sword and Belt together are sometimes seen as a pot or saucepan. Prominent in the middle of the Sword is the Orion Nebula, M42, a star formation region that looks like a fuzzy star to the naked eye but a beautiful region of nebulosity and young stars in a telescope or binoculars. At its heart is the Trapezium Cluster, a tight group of stars whose ulraviolet radiation makes the surrounding gas glow. The reflection nebula M78 can also be found in Orion using a small telescope, and the Horsehead Nebula, a dark region in the bright nebula of IC 434, lies south of the star Alnitak in Orion's Belt. The blue-white supergiant Rigel, at the top-left, is the brightest star in Orion, while the aging red giant Betelgeuse, at the bottom-right, is the second-brightest.
Following Orion's Belt to the right leads to Sirius, known to Maori as Takurua, which is the brightest star in the night sky. It is in Canis Major, the larger of Orion's two Hunting Dogs, and Canis Minor, the Smaller Dog is lower down, near the eastern horizon in the later evening. The brightest star in Canis Minor is Procyon, which is actually a binary system consisting of a main-sequence star and a white dwarf companion. To the left of Orion's Belt is the V-shape of stars representing the head and horns of Taurus the Bull. The Hyades Cluster resides here, and is one of the closest open star clusters to the Earth. Continuing around the sky, the Pleiades Cluster is another open cluster full of young, blue stars. In New Zealand it is called Matariki, meaning Little Eyes or Eyes of God, and its first pre-dawn appearance in June marks the start of the Maori year. The Milky Way stretches through these constellations and along the southern horizon, and along this line is the constellation Crux, currently low in the south-east later in the night. Beside it is the dark Coalsack Nebula, an interstellar cloud of gas and dust that obscures the stars beyond. To Maori it is Te Patiki, the Flounder.
- Mars is fairly high in the west after sunset, and this month Venus joins it, setting in the west-south-west about an hour after the Sun.
- Mercury appears late in the month, just below and left of Venus. Bright, golden Jupiter rises just after 01:00 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time) at the beginning of the month, and is up before midnight by the end.
- Saturn becomes a morning object during December, rising some 2.5 hours before the Sun by the end of the month.
- The Phoenicid meteor shower peaks on the 6th, its radiant in Phoenix being quite close to the star Achernar in Eridanus and well placed all through the night for southern hemisphere observers. Unfortunately, a full Moon will hamper viewing this year.
- The Geminid meteor shower is best seen after midnight on the 14th. The constellation is low in the north, even at its highest point at around 03:00 NZDT, so only around half the visible meteors can be seen from New Zealand.