Starwatch: the December night sky

The Summer Triangle of Vega, Deneb and Altair is dominating the high SW sky as our long December nights begin, while the smaller and less impressive Square of Pegasus is just as high in the SE. By our map times, the Square has shifted to the SW and the striking form of Orion is climbing in the ESE.

Orion’s Belt slants up to Aldebaran in Taurus, which stands to the right of the Moon on the night of the 3rd-4th and is occulted again early on the 31st, the star being hidden between 01:14 and 01:59 GMT for watchers in London and from 01:01 to 01:57 for Edinburgh.

Saturn is now lost from view in our evening twilight, while Venus, though brilliant at mag –3.9, rises less than one hour before the Sun on the 1st and soon disappears into the dawn twilight. It leaves Jupiter as the most conspicuous object (mag –1.7 to –1.8) in our morning sky. The giant planet rises in the ESE at about 05:20 on the 1st and 03:55 on the 31st and stands up to 20° high in the SE to SSE before dawn. Tracking ESE-wards in Libra, it passes 0.7° N of the double star Zubenelgenubi on the 21st.

Mars, much fainter at mag 1.7 to 1.5, stands above-right of Jupiter and moves from 3° above-left of Spica in Virgo to stand 3° to the right of Jupiter on the 31st.

Catch the waning Moon to the left of Mars and above Jupiter on the 14th. That morning also sees the maximum of the sparkling Geminids meteor shower, which lasts from the 8th to the 17th and brings meteors whose paths diverge from a radiant point above the star Castor in Gemini (star 6 on our chart).

If you found October’s Orionids and November’s Leonids to be disappointing, prepare to be impressed by the much more prolific Geminid meteors with their long tracks and medium-speed. Castor and the radiant climb from low in the NE at nightfall to pass high in the S at about 02:15 when, weather permitting, we may count a few dozen meteors per hour under a reasonably dark sky near maximum.

Mercury is a morning star low in the SE as the year ends. Between the 22nd and 31st it brightens from mag 0.5 to –0.3, rises more than 100 minutes before the Sun and stands around 8° high 30 minutes before sunrise.

December diary