Eyes on the Night Sky – December 2021
Welcome to the December edition of Eyes on the Night Sky. As always, we will select the best night sky objects to study with the unaided eye, binocular and telescopes. This month, we were spoilt for choice; there is a lot going on, so let’s hope there are plenty of clear skies. Wrap up warmly, grab a hot drink and get outside!
A Comet for Christmas?
Astronomers have been keeping a close eye on a comet that was first discovered on 3rd January 2021. All going well, it may brighten to unaided-eye visibility this month, providing stargazers with a Christmas treat. Comet C/2021 A1 (Leonard) has been travelling through our Solar System towards the Sun, where it will reach perihelion (a point closest to the Sun) on 3rd January 2022. As a comet travels sunwards, the sun’s radiation reacts with the comet’s nucleus, producing sublimated tails of ionized gas and dust as illustrated by a recent visitor, Comet Neowise. Of course, comets can be wildly unpredictable, so keep an eye out on the internet for the most up-to-date information.
The chart shows the position of Comet Leonard as it travels in the sky throughout December. For convenience, it shows the position at 6am every five days.
A Meteor Shower
On the early morning 14th December, the Geminid Meteor Shower will peak, producing bright and fast ‘shooting stars’. Despite the Moon being in its waxing gibbous phase, it’s worth keeping an eye out for the brighter meteors.
The radiant of this meteor shower originates right by the star Castor in the constellation of Gemini and is known to be cometary debris from 3200 Phaethon. This debris travels at around 80,000 miles (130,000 km) per hour and burn up 60 miles (100 km) above Earth’s surface.
A Lineup of Planets (and the Moon)
There is a still a chance to study Jupiter or the rings of Saturn this month: Jupiter sets at 9.15 at the start of the month and 8.30pm at the end. Saturn sets at 8pm the beginning of the month and 6.30pm at the end.
Look out in the early evening towards the southern horizon to see a pretty lineup of three planets and the Moon. The waxing crescent Moon passes underneath Venus, Saturn and Jupiter over five days, from 6th December to 10th December.
The New Moon falls on 4th December and Full Moon on 19th December.
Star Cluster Extravaganza
There are so many great stargazing wonders to explore this month and December is a great time to use your binoculars or telescope to find some pretty star clusters not too late at night. The winter skies are studded with a dazzling array of stars around the constellations of Cassiopeia, Orion, Taurus, Perseus and Auriga. In a dark sky it can almost rival the Summer Milky Way. The photographs illustrating each open cluster in this article will not look as detailed through telescopes or binoculars due to the way our eyes perceive light. Cameras are able to accumulate light and therefore capture more detail but it is still amazing to see these objects with our own eyes when they are unimaginable distances away from Earth.
Facing the east, look for a small grouping of stars in the constellation of Taurus, above the bright star Aldebaran. The Pleiades cluster isn’t just a pretty sight with the eyes, it appears as a collection of sparkling stars though 10×50 binoculars. Scan your binoculars slowly eastwards, in the constellation of Auriga and you will find three, binocular-friendly, open star clusters, M36, M37 and M38.
Move your binoculars upwards, look for the brightest star in the centre of the constellation of Perseus called Alpha Persei. Just below and to the left is a cluster of a few dozen stars which lie around 600 light years away. They are also known as the Alpha Persei Moving Group because although they look like a cluster and were born from the same nebula (hydrogen-based dust clouds) they are too dispersed to be classed as one but all move roughly in the same direction through space.
As we started with a spectacular open star cluster, we will end with another. Just underneath the ‘W’-shaped constellation of Cassiopeia and above the constellation of Perseus lies Caldwell 14 which is more commonly known as the Double Cluster. Comprising open clusters NGC 869 and NGC884, they lie 7,500 away from us and look like two compact balls of stars through binoculars. Each cluster contains around 400 stars and really look stunning in a dark sky, away from man-made light pollution.