The Moon visits multiple planets, Mars continues its trek through the summer constellations, and one of the most spectacular meteor showers of 2021 lights up the heavens. The December sky will be extra festive this year.
A sloping alignment of planets at sunset
While Jupiter and Saturn have been gracing our evenings and nights for several months now, they are currently in the area of sky that disappears in the west before 10 p.m. And as the Sun gradually heads their way, they set earlier and earlier. They are now quite close to the very brilliant Venus, unmistakable as the Evening Star once the Sun dips beneath the horizon.
The Shepherd’s Star was at its greatest elongation in October and is now continuing its relentless descent toward the Sun at twilight. Venus is still easy to spot in the first half of December, reaching maximum brightness on the 9th. By the end of the month, it becomes increasingly difficult to see in the twilight glow. Any small telescope will allow you to observe what Galileo discovered more than 400 years ago: Venus has phases, and it currently appears as a progressively thinner crescent as the days go by.
In the early evening, Jupiter, Saturn and Venus form an almost perfect line, stretching diagonally from the south to the southwest. Shortly after sunset, they start appearing one by one, in order of decreasing brightness. Venus is first, low and close to the southwestern horizon. Then comes Jupiter, about 30 degrees above the southern horizon, followed by the far more timid Saturn, located right between the two. Although it’s fairly inconspicuous, the Ringed Planet is unmistakably bright against the faint background stars of Capricornus.
In early December, the Moon visits each planet in turn. On December 6, you can try catching a glimpse of the first crescent Moon about 3 degrees below Venus; it will be very difficult to observe as this razor-slim crescent is easily lost in the twilight glow and disappears early below the horizon. The chances of seeing this celestial quartet (Moon, Jupiter, Saturn and Venus) are better on December 7, when the Moon will be 5½ degrees below Saturn, higher up in the sky. Although still quite slim, the lunar crescent will be much easier to spot than the previous night. On the 8th, the Moon hangs between Jupiter and Saturn, and on the 9th, it forms the fourth and final signpost of the Venus-Saturn-Jupiter-Moon lineup. The scene is still visible on the 10th, with the Moon completing the sloping alignment of planets.
An abundance of shooting stars
Mid-December is marked by the usual Geminid meteor shower. This is the most consistent and reliable shower year after year and one of the most prolific, second only to the Quadrantids. A peak of up to 120 meteors per hour is what we would see in a beautiful clear sky with the radiant at the zenith. But even though the constellation Gemini (from which the Geminids appear to originate) cannot reach the zenith at our latitude in southern Quebec, it does climb high enough in the middle of the night for a very good view.
The best time to observe the Geminids is during the night of December 13 to 14. In fact, although the Moon is in a waxing gibbous phase—and therefore quite high in the sky in the first half of the night—the shower is only expected to peak at around 2 a.m. That’s when the Moon is just about to disappear below the horizon and the constellation Gemini is still close to the meridian—excellent conditions that will continue until dawn.
Mars dons a summer look
Early risers will get a chance to put their skills to the test and relive summer memories. That’s because Mars is still trekking through constellations that are typically visible during the warm evenings of June and July. On December 2, shortly after 5 a.m., experienced observers will be on the lookout for the very thin crescent Moon next to the star Zubenelgenubi. As the clock ticks forward, all of Libra rises, followed by the glorious Mars, 7½ degrees below the Moon. Although this scene presents a viewing challenge, your best bet to catch a glimpse is about 45 minutes before sunrise. But the next morning, on December 3, 30 minutes before sunrise, it will only be visible to observers who have a perfectly clear view of the southeastern horizon. With the Moon only one day away from being new, spotting the crescent, located 7½ degrees below the equally elusive Mars, will be a major challenge.
The Red Planet quickly exits Libra and wanders close to the head of Scorpius as of December 17. With each passing day, its rapid trek leads it to Antares, and by the end of the month the two are a mere 5 degrees apart. This is a great opportunity to compare Mars and Antares, its reddish rival. Mars, the Roman god of war, personified as the planet of the same name, was also known as Ares in the Greek pantheon of deities. The red heart of Scorpius, similar to Mars in magnitude and colour, was named “Anti-Ares” or Antares—literally, the “rival of Mars”—to distinguish the wandering celestial body from the fixed star, while also highlighting their obvious similarity. The last days of December are a great time to observe the two red spots competing with each other above the southeastern horizon just before the Sun comes up. Those who like a challenge can cap off 2021 by trying to spot the whisker-thin crescent Moon as it forms a very compact triangle with Mars and Antares; they can meet this challenge one hour before the final sunrise of the year.