December night sky

By CLIVE JACKSON [email protected]

Clive Jackson is an amateur astronomer and an imagineer who does his best to understand the universe. He is also the director of the Astronomical Observatory of Tavira (Sitio do Malhão, Tavira) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.

Welcome to the December night sky. This is the month of the longest nights and shortest days of the year. The Sun is at its lowest point in the sky on the 21st at 5.47pm.

This is called the winter Solstice and officially it marks the start of winter in the northern hemisphere, although it makes more sense to think of it as midwinter because after this date, the Sun starts to climb higher in the sky and the days grow longer (but not much warmer).

By 9.30pm, over in the eastern horizon, the red planet Mars is visible in the constellation of Leo but it will move into the constellation of Cancer the Crab in January when it will be at its brightest. The last quarter Moon will be below Mars on the night of the sixth.

The giant planet Jupiter is still visible in the constellation of Capricorn but sets in the west by 10pm.

If you can stay up until after 2am on a cold clear winter’s night, you will see the ringed planet Saturn rising in the east in the constellation of Virgo.

On the night of the 13th to 14th, it is the peak of the Geminid meteor shower. This is the best regular shower in December but, as always, you would have to be patient.

This month has two full Moons – the first on the 2nd and the other on the 31st. The second full Moon is sometimes known as a Blue Moon.

On average, there’s a Blue Moon every two-and-a-half years. If a full Moon occurs on the night of October 31 (Halloween), then it would be also a Blue Moon. Even though the average period is quite short, the fact is the next Blue Moon visible from Europe will not be until the year 2020.

In religious festivals that depend on the phase of the Moon, for example Easter, the exact dates are very important. In fact, in the Middle Ages, when the full Moon did not fit in with the calendars they had at that time, they blamed the Moon for being wrong and called it a liars Moon.  The full Moon at the Autumn Equinox is called the Harvest Moon and the full Moon at the spring Equinox is called the Hunters Moon.

The Moon is Full on the 2nd, Last Quarter on the 9th, new on the 16th and First Quarter on the 24th and full Moon on December 31.

Clive Jackson is the Director of the Tower of Tavira – Camera Obscura (next to the Castle in Tavira), Tel 281 321 754, Fax 281 324 688 or email: [email protected]. Visit