And so we come to the month that contains the shortest day of the year, the winter solstice. More exciting, you might think, is the fact that this month contains Christmas!!
There are many exciting things to see in the night sky before and even during that great event though, so buckle up while we go on a tour of the night sky in December.
The first event that takes place this Month in the celestial sphere is all about the planet Mercury. Usually, Mercury is a hard planet to spot, especially in the Northern Hemisphere. It doesn’t venture far from the sun in the sky at all (which you can imagine, given our relative positions in the Solar system). Mercury is either outshone by the sun, or barely rises above the horizon during sunset. So you have to be committed and punctual to spot the smallest planet!
Image Credit: NASA
The big event that takes place on the 4th of December is Mercury being at its greatest eastern elongation. Now what that actually means is that it is at its furthest point away from the sun in our skies, so it is the easiest time to view the planet. If you’re interested in the maths of it, it will reach 21 degrees from the sun, with its maximum ever being 28 degrees.
In the next week of December look towards the moon. The moon is a familiar sight to humans as it goes through its phases over the course of the month (on average, 29.5 days to be precise). Its darkest phase, the new moon, where the moon lies between the sun and the earth (but not aligned in the right way to be a rare solar eclipse) will take place this month on the 12th, and this is the best time to look at the night sky, unaffected by the bright light of the moon. December is also a particularly good month to do some stargazing, as we have a good selection of constellations visible in the night sky, so take this chance to head out.
The Geminids Meteor Shower. Image Credit: NASA
The cherry on the cake of this good timing is the meteor shower that will peak on the 13th and 14th of December, made even more spectacular by the moon being new. This shower is the Geminids, the best meteor shower of the year. The meteors from this shower (as you might guess) radiate from the constellation of Gemini, and this is one of only two major showers in the year that originate from an asteroid, as opposed to a comet.
Usually, meteor showers are each associated with a comet, which on its long oval path around the sun, leaves a long trail of debris behind it. Every year at roughly the same time, the Earth then passes through this debris trail on its orbit around the sun. This shower, unlike most of the others, is associated with not a comet, but an asteroid. The asteroid in question is called 3200 Phaethon, an unusual asteroid whose orbit is a little more comet-like than other asteroids. So much so in fact, that it is sometimes called a rock comet. The parent body of the Geminids meteor shower was a mystery until 1983, when Phaethon was discovered, as it had been assumed that only comets could generate meteor showers.
Look out for the Geminids radiating from the constellation of Gemini in the East of the night sky all night, but especially after midnight.
We also have a more minor meteor shower, caused by comet Tuttle, a few days later – on the 21st and 22nd of December the Ursids meteor shower will peak. This is a much more sedate shower though, with around 5-10 meteors per hour at its peak. And of course the moon has carried on further through its phases by this time, meaning some of the meteors might be drowned out by the light of the waxing gibbous moon.
Also on the 22nd December we of course have the winter solstice, the shortest day of the year and the first official day of winter in the northern hemisphere. Of course, if you are in the southern hemisphere, it is the first day of summer, and the longest day of the year. Anyone wishing they were in the southern Hemisphere?
Image Credit: Wikimedia
However, if you want to celebrate the solstice, we can look back to the past. It has been marked since the neolithic times, as a sign of when to plant crops, and how best to monitor food reserves. Original celebrations marked the life, death and rebirth cycle, as the old year died and the new year was reborn. Estimation of time was incredibly important during the ‘famine months’ where food was scarce. Cows were often slaughtered at the winter solstice to avoid having to feed them through the winter, so why not make a celebration on one of the few times of year that meat is plentiful!
One of the constellations that you can see in the night sky this December is Orion, who is spectacular to look out for in the winter sky, but you do have to wait for winter to see it at its best! Orion is a really famous constellation recognizable by his belt. The belt is made up of three stars, below which is Orion’s sword, which can point us towards the amazing Orion Nebula. Now you do need a telescope to see this in all its glory, but it is definitely worth looking just with the naked eye. You’ll see a diffuse blue cloud expanding out from a central point, which represents the clouds of gas and dust that new stars materialise from. The Orion Nebula is the closest large star-forming region to Earth.
Image Credit: Stellarium/Anna Taylor
Also in the constellation of Orion are two stars that demonstrate the life cycle of large stars beautifully. These stars are Betelgeuse and Rigel and they are at opposite ends of their life cycles. The star Rigel is a blue supergiant star, roughly 20 times the mass of our sun, and thousands of times as luminous. Blue stars are usually hot stars, in the early stages of their life cycle, and this is true of Rigel. It is a star only a few million years old – this is still a star early in its life cycle. Betelgeuse on the other hand is an older star, a red supergiant. Due to the fact that large stars live shorter, more dramatic lives than stars the size of our sun, Betelgeuse is younger than our sun (10 million years old compared to our sun’s 5 billion years) but in a later stage in its life cycle. It is reaching the point where it may soon go supernova (our sun is too small to ever go supernova – it will take an alternative path). In fact, a few years ago Betelgeuse dimmed dramatically, and we thought it was about to explode! However it turned out that it was just obscured by some dust – a very mundane reason for what we thought was going to be an exciting phenomenon.
Image Credit: freeimages.com
So take a chance this winter on clear nights to look out at our universe – you won’t regret doing so. Make sure you wear thick socks, though!
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