With the winter solstice leading the way towards the season that sees the constellation of Orion in the northern skies as the protagonist, the sky of December 2019 will be propped up with “shooting stars”, conjunctions, and the planets that until now have made it by master, Jupiter and Saturn, come close to unobservability.
They then leave space for the luminous Venus. It will shine in the heavens until many hours after sunset, leaving no doubt about the proverbial vanity attributed to the planet and to the goddess of Love Venus, who so loved to be admired.
The month of December opens with interesting conjunctions. First of all that of the day 11 between Venus and Saturn, in the constellation of Sagittarius, towards the South-West horizon.
In Libra we can instead observe, on the 23rd, the astral encounter between the Moon and Mars.
On the 27th a Saturn at the limits of observability will duet in the sky with a sickle of Moon, barely perceptible too.
On the evening of December 29, the Moon and Venus will offer us the last conjunction of the year. They will find themselves towards the southwest horizon, in Capricorn.
As already announced, the beautiful constellation of Orion will dominate, recognizable in the sky thanks to the three stars that form its belt (Alnitak, Alnilam and Mintaka). These remind us that we have now arrived in the astronomical winter: winter solstice will be the 22nd at 03.58am. The Sun will therefore reach its maximum distance below the celestial equator; the day will be the shortest of the year.
The stars Sirio, Betelgeuse and Procione form the asterism of the winter triangle, which contrasts with the summer triangle. To the north of asterism, we find the constellation of Gemini, while to the north-west of Orion we find Auriga and Toro. The summer constellations, including the Swan, set.
Mercury rises about an hour and a half before the Sun, on the East horizon, becoming then unobservable towards the end of the month.
Venus increasingly visible, the planet of Love will be observed up to three hours after sunset, offering two conjunctions during the month (with Saturn on 11 December; with the Moon on 29).
Mars rises just before Mercury towards the East horizon. In conjunction with the Moon 23 in the constellation of Libra.
Jupiter. Day 27 will be in conjunction with the Sun. It is therefore impossible to observe it throughout the month of December.
Saturn. Very low on the West horizon, it will become undetectable towards the end of the month, moving towards its conjunction with the Sun of 2020.
Uranus moves with retrograde motion in the constellation of Aries, at the limits of visibility with the naked eye. You will then need an optical instrument to observe it.
Neptune will be observable in the first hours of the night in a southerly direction. Also in this case it will be necessary to use a telescope to admire it, in the constellation of Aquarius.
The Geminids are the most anticipated meteor shower of the month. Thanks to their very high ZHR (Zenithal rate), about 120 meteors are expected per hour. Visible from 7 December and up to 17, they seem to radiate from the constellation Gemini (hence their name).
On the 17th the Geminids pass the baton to the lesser known Ursidi, “falling stars” peaking on December 22, but with a smaller ZHR. Therefore, fewer “shooting stars” will be visible but equally spectacular; vision also favored by the absence of the Full Moon. Ursids radiate from the Ursa Minor.