Our Night Sky: December 2023

You don’t have to be out late to go stargazing this month because December is the month of the Winter Solstice and when we have our shortest day with under 7 hours of daylight.  Although most of the bright stars are now missing from our sky, it is a good time to spot the Andromeda Galaxy, the closest spiral galaxy to our own galaxy, the Milky Way. All the planets, except for Mars will be visible during the hours of darkness this month and can be spotted with a pair of binoculars or a telescope. Finally, we have the Geminids meteor shower peaking on the morning of 14 December and with no Moon in the sky to spoil the show, it may be possible to see up to 120 meteors an hour, so do look out for them then.

Magical Mushroom I - Sailean nan Cuileag, Sunart
A carved wooden mushrooms in the woods around Sailean nan Cuileag, sits capped with snow under a clear night sky

​The Constellations

This month the sun sets around 4:00 pm and the stars and the constellations start to become visible from about 6:00 pm. As with November, there is a great signpost in the form of the Square of Pegasus to help you find your way around the sky. It is a huge square made up of four stars of nearly equal brightness: Scheat, Alpheratz, Markab and Algenib and you should be able to see it high up in the south, above Jupiter in the early evening sky.
 
The top left star of the Square is Alpheratz. It is the brightest star in the constellation of Andromeda, which is marked by a line of three more stars running up and to the left of it. You can use this line to find the Andromeda Galaxy, one of the most famous features of the night sky and the nearest spiral galaxy to our own, the Milky Way. The best way to find it is to start Alpheratz and go a further two stars along the line, turn right and count another two faint stars along, and the Andromeda Galaxy (M31) will be close to the second faint star. If you are in a town, you’ll probably need a pair of binoculars to spot it, but if you’re in a dark place out in the country, you should be able to pick it out without using binoculars. 

Below Andromeda and to the right of the Square is the Constellation of Aries (the Ram), whose three main stars form an easily recognised triangle. Above this, you will find another triangular shaped constellation, called Triangulum (the Triangle), which contains the Triangulum Galaxy (M33), our next closest galaxy after the Andromeda Galaxy. This will be visible with binoculars if you are under a good dark sky.
 
Over to the left of Andromeda, you will find the Constellation of Taurus (the Bull), which can be readily found by spotting Aldebaran, the bright orange giant star that marks the eye of the Bull whose face is depicted by a V-shape of stars to the right. Look below and slightly to the left and you will find Orion (the Hunter). It is most easily spotted by picking out the line of 3 stars that makes up Orion’s Belt. 

The Constellation of Andromeda
Image Credit: Till Credner [CC Share Alike 3]

There will be more about Taurus and Orion next month, but for the moment, draw a line using the three stars in Orion's belt and follow it through Aldebaran and you’ll find the Pleiades star cluster (M45) a bit beyond it. This cluster is the brightest open constellation we can see in the night sky and is a grouping of more than 1,400 stars, seven of which are visible to the naked eye. The name comes from the early Greeks who referred to the constellation as the Pleiades, or the Seven Sisters who were daughters of Atlas and Pleione. These stars are mentioned three times in the Bible and are linked to origin stories for many American Indian tribes.

Southern Night Sky - December
Created using SkyPortal Mobile App

Northern Night Sky - December
Created using SkyPortal Mobile App

If you look north, you’ll see the same stars as you would in any other month, but their orientation varies from month to month. In December the familiar Plough asterism, which many people recognise, is moving from the north to the north-east. If you follow its two right-hand stars upward and veer a little bit to the right, you’ll find Polaris, the Pole Star. If you look high up over to the north-east, you can see Castor and Pollux, the two brightest stars in the Constellation of Gemini (the Twins), which represent the heads of The Twins. Meanwhile, low down in the North-West, you will find Vega, the brightest star in the Constellation of Lyra (the Lyre). It is the fifth-brightest star in the night sky, and the second-brightest star in the northern celestial hemisphere after Arcturus.

​The Moon

There was a full Moon on 27 November, so we start the month with an 82% waning gibbous Moon that becomes a last quarter Moon on 5 December. 

The new Moon (no moon) is on 12 December and a few days before that, on 8 December, you can see a crescent Moon sitting above and to the right of Venus over in the southeast from 3:00 am and until the sun rises at around 8:45 am. You should also be able to see a crescent Moon at daybreak on 9 December, when it will be at its closest to Venus and again on 10 December when it will be below and to the left of the Morning Star. Alternatively, a few days later, on 15 and 16 December, you should be able to pick out the thinnest of crescent Moons sitting low in the southern sky as the Sun sets, while on 17 December the Moon will be very close to Saturn.

We have a first quarter Moon (a half-moon) on 19 December. You will see it in the south-eastern sky as darkness falls and it will remain visible until it sets just after midnight. Then, on 21 and 22 December, you will find over in the southeast sitting very close to Jupiter.

The Moon becomes 100% full at precisely 0:33 am on 27 December. This means that it will appear full on the nights of 25-26 December, 26-27 December and 27-28 December. It will rise in the northeast at around 2:00 pm on 25 December, at about 2:30 pm on 26 December and at about 3:30 pm on 27 December.
 
This month’s full Moon is called the Cold Moon because December is the first month of winter. Its Old English/Anglo-Saxon name is the Moon Before Yule, while another name for it is the Wolf Moon, however, this is more commonly used for January’s Full Moon.

​The Planets

Soon after sunset at the beginning of the month, use binoculars or a telescope to look out for Mercury low down on the southwestern horizon. The innermost planet will be at its greatest separation from the Sun on 4 December, meaning that it will be shining at its brightest. After that, it will fade each night before disappearing in the twilight glow during the second week of the month.
 
As darkness falls, you will also see Saturn sitting above the southern horizon.  It will be visible until it sets at around 10:00 pm and if your binoculars or telescope magnify by about 40 or 50 times, you be able to see its famous rings and its biggest moons when you look at it. The largest, Titan, is enormous. In fact, it’s 40% more massive than the planet Mercury and 80% more massive than our own Moon.
 
To the left of Saturn, you will find Neptune. In contrast to Saturn, it will be quite faint, so you will need a telescope to pick this outermost planet in the boundary between Aquarius and Pisces in the southeastern sky. This is because its distance from Earth means that its brightness is half of that of the faintest star you can see with the naked eye. It sets at just after midnight.
 
Next is Jupiter, which you will find it over in the east as darkness falls and it will remain visible until it sets at around 4:30 am. If you look at it through binoculars, you will see some tiny starry objects on either side of it. These are its brightest and largest moons. They are Io, Europa, Ganymede, and Callisto and are known as the Galilean moons and will change position each night as they circle this mighty gas giant planet. If you use a telescope, you will be able to see its roiling clouds and the huge storm known as the Great Red Spot.
 
Uranus lies to the left of Jupiter and does not set until around 6:00 am. You may be able to spot it with the naked eye, but you’ll stand a much better chance of seeing it if you use binoculars or a telescope. In fact, a telescope should reveal its disc and its largest moons.
 
Next up is Venus, rising in the southeastern sky at around 5:00 am and continuing to spend this time of the year as the glorious “Morning Star”. It will be easy to spot because it will be shining much brighter than anything else in the sky except for the Moon.
 
Mars is too close to the Sun to be seen this month.

Meteor Showers

December is the month for viewing the shooting stars of the Geminids Meteor Shower. Unusually, they are not debris from a comet, but rather debris from an asteroid called Phaethon. The Geminids have become more plentiful in recent years and are considered by many to be the best meteor shower of the year. They are active from 4-17 December and during their peak, which this year is on 14 December, it can be possible to see around 120 meteors per hour.
 
Their radiant point is in the north-east sky, in the Constellation of Gemini (The Twins) and close to Castor, one of its two bright stars. Although this is where they originate from, you’ll be able to see them at any point across the sky as they burn up in the upper atmosphere, some 60 miles (100 km) above Earth’s surface.
 
The best time to look for them is normally when the radiant point is at its highest in the sky, which will be at around 2:00 am. This year, there will be a waxing crescent Moon on 14 December, which sets at 4:30 pm, meaning that it will not illuminate the sky and spoil the show.

Winter Solstice

This year, the Winter Solstice will occur on 22 December at 3:27 am and is the exact moment when the northern hemisphere is tilted furthest away from the Sun. However, many people refer to the Winter Solstice as the Shortest Day of the year, when the number of hours of daylight are at their minimum and the number of hours of night are at their maximum. On 22 December this year, our sunrise will be 8:55:40 am and our sunset will be 3:47:34 pm, giving us only 6 hours, 51 minutes and 54 seconds of daytime.