The night sky in December sees the late summer/autumn constellations stand out soon after sunset. It also welcomes some familiar winter constellations as well as the bright planet Jupiter – which rises by late evening around the last two weeks of the year, with Venus and Mars in the vicinity. These planets are located in and around the constellation Leo, the lion, and will feature more in the spring skies next year.
Using a pair of binoculars one can see Jupiter’s four largest moons, discovered by Galileo in 1610. Through a telescope one can also see the shadows cast by these moons on Jupiter’s atmosphere.
The summer triangle is still visible, with bright star Vega in the west-northwest, Deneb higher up and Altair in the west-southwest.
The centre of the Milky Way galaxy is not visible; however as it is now below the horizon, but there is still a good portion of the galaxy that can be seen streaking high across the sky if viewed from locations with no light pollution.
The W-shaped constellation Cassiopeia is easy to find towards the northeast. Use it to find the north star Polaris, as the W shape faces north. Polaris is as bright as the stars in Cassiopeia and is located in a region of space quite devoid of stars. Close by one can also see the Great Square of Pegasus, nearly in the middle of the sky. This is followed by Andromeda in the northeast with Perseus just below.
Our galactic neighbour, the Andromeda galaxy (M31) is now very high in the middle of the sky and is visible with the naked eye on dark nights.
Astronomers estimate there are around 200 billion galaxies in the observable universe. The ‘observable’ universe is only a part of the entire universe, which as far as we know is infinite. The largest galaxies are hundreds of thousands of light years across, each containing many billions of stars. The smallest dwarf galaxies, by comparison, are a few hundred light years across with a few thousand stars. Most galaxies, including ours, are spiral in shape, due to their rotation.
Up along the eastern horizon one can see the winter stars beginning to rise. The stars of Taurus the bull are now up in the east with the bright yellowish star Aldebaran and the Pleiades (also known as the Seven Sisters) star cluster. There are over 200 stars in this region of space. Use binoculars to see many more stars than you can see with the naked eye.
Another constellation easy to spot is Auriga (the charioteer) with its bright star Capella. Orion the hunter also can be seen due south, later in the night. The distant planet Uranus, notable due to its bluish colour, is also visible; however one needs a good pair of binoculars and a finder chart to see it. This is available on the Astronomical Society’s website. A telescope will show a tiny disc rather than a sharp pinpoint of light, as with all the stars.
The second week of December onwards may be a good time to see a new comet in the sky – C/2013 US10 (Catalina). This may become a binocular or even a faint naked eye comet in Virgo. It will get closest to the Earth in January 2016. No one knows for sure how bright it will become or whether its tail may grow or not in the coming weeks. Comets are unpredictable, and that is one of their most intriguing characteristics.
The comet’s trek around the sun will give it enough energy, like a slingshot, to allow it to escape the solar system, never to return, as it wanders forever the depths of the Milky Way galaxy.
www.maltastro.org
Alexei Pace is president of the Astronomical Society of Malta.
Astronomical events in December
Thursday: Last quarter moon
December 11: New moon
December 14: Peak of Geminid meteor shower; favourable conditions – no moonlight
December 18: First quarter moon
December 21: Earth at its southern solstice; winter begins in the northern hemisphere
December 25: Full moon
December 28: Mercury at its greatest elongation (east); visible in the evening sky after sunset.