Northern Hemisphere

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during December 2013.

Pegasus and Andromeda are setting towards the west after nightfall, and you can find the galaxies M31 and, given a dark sky, M33, in this part of the heavens. Aries and Taurus are over to the east, the latter containing the Pleiades and Hyades star clusters. The red star Aldebaran appears to be within the Hyades, but is actually closer to us. Orion rises a little later, and you can follow the three stars of his Belt down to the brightest night-time star, Sirius, in Canis Major. Beneath the Belt is the fuzzy glow of the Orion Nebula, a stellar nursery which is a rewarding sight in binoculars. Gemini, the constellation of the Twins, is nearby. High overhead are Cassiopeia and Perseus, with the picturesque Double Cluster between them.

The Planets

• Jupiter rises around 19:30 UT (Universal Time) at the beginning of the month, reaching its highest elevation of 62 degrees when due south at about 03:00. It shines at magnitude -2.6 and has a disc spanning 42", making this a great time to observe it. It lies in Gemini and, in the 10th, passes just 15' from the star Wasat, which has a magnitude of +3.5. It is at its nightly highest point around midnight by the end of December, and you can see its equatorial bands and larger moons, as well as the Great Red Spot at certain times.
• Saturn is a pre-dawn object, rising around 05:00 UT as the month begins, and 03:30 at its end. With a magnitude of +0.6 and a disc 15.5" across, it now shows its rings at 20 degrees to our line of sight, allowing them to be easily observed through a telescope. It reaches only about 20 degrees above the horizon, however.
• Mars has moved from Leo into Virgo and rises soon after midnight early in the month, with a magnitude of +1.2 and an angular size of 5.6". During December, it brightens to magnitude +0.9 and grows to 6.8" in size, allowing surface features such as the polar caps and Syrtis Major to be seen. Towards the end of the month, it approaches the star Porrima.
• Mercury shines at magnitude +0.6 in the pre-dawn sky as December begins, appearing below Saturn. It brightens to magnitude -0.8 by mid-month, but gets progressively lower at dawn and becomes lost in the Sun's glare around the same time. It reaches superior conjunction (behind the Sun in the sky) on the 29th.
• Venus is spectacular, starting December at magnitude -4.9. Although only 15 degrees above the horizon at sunset, it can be observed at a higher elevation for at least an hour before that. It changes significantly during the first three weeks of December, its illuminated fraction decreasing from 30 to 11 percent even as its angular diameter grows from 38 to 53". It is just 4 percent illuminated by month's end, but the slender crescent is almost 60" across. By making these observations, you can follow in the footsteps of Galileo, to whom the changing phase of Venus revealed that it must be in orbit around the Sun and not the Earth. The planet will pass in front of the Sun (inferior conjunction) on the 11th of January.

Highlights

• Comet ISON passed close to the Sun on the 28th of November, before recording of the current Jodcast episode. The progress of its brightness this month remains unpredictable. Despite initial reports of its demise, parts of the comet survived and the tail may yet become visible to the naked eye during early December, below a thin crescent Moon and the planets Saturn and Mercury. It will reach higher in the sky at daybreak as the month goes on, becoming visible before twilight in mid-December. Although its brightness is then expected to decline, it may be seen 5 degrees to the west of the globular cluster M13, in Hercules, on the 22nd. It becomes circumpolar towards the end of the month, lying in the vicinity of Ursa Major.
• The Moon occults the star Epsilon Piscium at about 22:05 UT on the 11th (commencing at 22:07 from Edinburgh and 22:16 from London, for example). The star, shining at magnitude +4.3 in the constellation of Pisces, is at 30 degrees' elevation in the south when the waxing gibbous Moon passes in front of it. It will be seen to vanish as the dark limb of the Moon obscures it, emerging less dramatically from the bright side about 13 minutes later.
• The Geminid meteor shower can be observed after midnight around the 14th and 15th, with the radiant (from where the meteors appear to come) near the bright star Castor in Gemini. The gibbous Moon in Aries hinders the view, but after it sets, around 05:00 UT, there should be an hour of darkness in which to spot the meteors. These shooting stars are produced by dust shed from the asteroid 3200 Phaethon, whereas most showers are cometary in origin.
• The Ursid meteor shower is visible after midnight on the 22nd and 23rd, with its radiant not far from the bright star Kochab in Ursa Minor. A gibbous Moon is again present, but poses less of a problem as it is far from the radiant in the sky.

Southern Hemisphere

John Field from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during December 2013.

The evening sky is dominated in the north by the constellations of Taurus, Orion, Canis Major and Canis Minor. The Milky Way stretches through them and along the southern horizon, its pattern of light and dark regions dimmer than in the winter, but still impressive. It comprises many distant stars in our galaxy, combined with patches of obscuring dust. M42, the Orion Nebula, appears as a bright cloud within Orion the Hunter. Upside-down in the southern hemisphere, Orion is sometimes called the Cooking Pot, his Belt of three blue giant stars marking its base. Orion's Sword, containing M42, is one of the Pot's sides. The nebula is part of a large cloud of interstellar material, and a telescope reveals patterns, while photographs show different colours. Beneath the Pot is Betelgeuse, a red giant star which forms one of Orion's shoulders, while above is the blue-white giant Rigel, one of his feet. Rigel has a companion star that can be seen in medium-sized telescopes. The upside-down V-shape of Taurus is to the west of Orion, forming the head of Taurus the Bull. The bright star Aldebaran marks the Bull's eye, while the more distant Hyades Cluster is part of the head. The Bull's back is marked, a little further west, by the Pleiades Cluster, which to Maori are known as Matariki, or the Little Eyes. At least seven stars of the Pleiades can be seen by eye on a dark night, and binoculars reveal many more.

Crux is low in the south-east in the evening, with the dark Coalsack Nebula beside it. The darkness is caused by clouds of material which may one day collapse under gravity and form stars. The Large and Small Magellanic Clouds (LMC and SMC) appear as bright clouds in the southern hemisphere sky, and are satellite galaxies of the Milky Way. The LMC is near to the bright star Canopus in the south-east, and binoculars or a small telescope can be used to find many star clusters and nebulae within it. The SMC is not far away and is close to the globular cluster 47 Tucanae, which looks like a hazy star to the unaided eye but can be seen to be a round group of stars through binoculars. NGC 362 is another nearby globular cluster, but a telescope is needed to observe it well.

Highlights

• The annual Phoenicid meteor shower reaches its peak on the 6th. The meteors seem to come from a point called the radiant, which is in the constellation of Phoenix for this shower, near to the bright star Achernar. It is high overhead, well placed for observing.
• The Geminid meteor shower peaks on the 14th. The radiant, near to the star Castor in Gemini, rises at about 03:00 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time), and its low elevation means that only half the meteors are visible. The Moon, becoming full on the 17th, hampers viewing, but the shower is worth seeing a week either side of the peak, and so the beginning of the month may be a good time to observe without the Moon's glare.
• The planet Jupiter also sits in Gemini this month, its larger moons visible through binoculars. It appears as a brilliant white star to the naked eye.
• The summer solstice occurs in the southern hemisphere this month, with the longest day coming on the 21st. The Sun is currently at a peak of activity, with many sunspots visible - but only look at them via a projection or through a dedicated solar telescope, as other methods may damage your eyesight.
• Comet ISON has now left southern hemisphere skies, but brightened to naked eye visibility last month before doing so. It is still visible to those at low southern latitudes early this month.