Starwatch: The December night sky

Graphic: Finbarr Sheehy

Orion stands clear of Britain’s ESE horizon at our map times as the glorious starscapes of winter invade from the east. Above Orion lies Taurus with the Pleiades and the bright star Aldebaran which is occulted by the almost-full Moon on the 23rd. Times vary a little across Britain, but for London the star is hidden from 18:10 to 19:12.

Above and to the left of Orion is Gemini with its two leading stars, Castor above Pollux. Meteors of the Geminids shower fly in all parts of the sky between the 8th and 17th, their paths diverging from a radiant point that lies close to Castor and crosses high in the south at 02:00. Now giving our best annual meteor display, the Geminids have plenty of medium-slow bright meteors and peak on the 14th with more than 100 per hour visible to an observer under an ideal sky. With no moonlight to interfere, the nights of 13/14th and 14th/15th could be memorable.

It is not until almost four hours after our map times, as Orion reaches the meridian, that the first bright planet of the night rises in the E. Jupiter, conspicuous at mag –2.0 to –2.2, lies in SE Leo and climbs well up into the S by dawn. A telescope shows it as 36 arcsec wide when it is close to the Moon on the 4th.

Venus, mag –4.2 to –4.1, trails almost 35° behind Jupiter on the 1st. However, their separation doubles as Venus speeds ESE-wards during December, dipping lower into our SE predawn sky while its dazzling gibbous disc shrinks from 17 to 14 arcsec across. Venus stands 4° NE of Spica in Virgo on the 1st, moving to lie 2° NE of the famous double star Zubenelgenubi in Libra on the 18th and a similar distance NW of the tighter double Graffias in Scorpius on the 31st. As it is overtaken by the waning Moon on the 7th, it is occulted as seen from much of North America.

Mars, much fainter at mag 1.5 to 1.3, lies roughly halfway between Venus and Jupiter in our sky and passes N of Spica on the 21st. Saturn, mag 0.5, hovers low in our predawn SE sky after mid-month while Mercury may be glimpsed during the final week of 2015 as it shines at mag –0.4 and stands only 5° above our SW horizon 30 minutes after sunset.