To help you learn about the southern night sky, Sydney Observatory provides an audio guide/podcast, transcript of that audio, and a sky map or chart each month. This month’s guide is presented by Geoffrey Wyatt, Sydney Observatory’s Astronomy Programs Producer.
See the Sky Chart
We provide a December 2018 night sky chart (PDF) which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.
Read the Guide
‘For some, who are travelers, the stars are guides. For others they are no more than little lights in the sky’ as said by Antoine de Saint-Exupery from The Little Prince. That you are here listening to this would seem to indicate that you are a traveller and I will help you on your journey through the night sky. Hello there, this is Geoffrey Wyatt and I’m one of the Education team here at the Museum of Applied Arts Sciences’ Sydney Observatory, I’m going to talk to you about what’s visible in the sky for the month of December.
This audio guide, transcript and printable sky map are all available free from our website at www.maas.museum where you find a link to Sydney Observatory and the monthly sky guides.
To get the most from this podcast, you’re going to need some resources including a map of the December night sky, either from our webpage or from, ‘The Australasian Sky Guide’ by Dr Nick Lomb.
At this time of year it should be quite nice outside, so a nice comfortable blanket to sit on and perhaps a drink of your choice as well.
Most importantly I think you need patience, a sense of adventure and imagination.
Most of us can find the four cardinal directions. North, east, south, and west. Depending on the time of year the Sun generally sets in the west and rises in the east. With a little thought we can then find north and south.
If we consider this in a little more systematic way we can find our direction around the horizon starting from the north and moving in a clockwise direction as seen from above. East would be 90 degrees azimuth, that is, 90 degrees east of north. 180 degrees azimuth is therefore south. 270 degrees is west, and so on. That part is relatively easy.
Now consider how high from the horizon something might be?
What I want you to do therefore is to hold out your hand at arm’s length. Clench your fist, but then hold up your pinkie. For most people, regardless of age and size, because the proportions are all pretty much the same, a pinkie at arm’s length will cover roughly one degree of the sky or twice the size of the Full Moon.
Close in the finger in so you’ve got a clenched fist, and you’ve got a marker for roughly 10 degrees. Outstretched fingers and thumb from pinkie-tip to thumb-tip and you have 20 degrees. With a little practice you’ll be able to do it with ease.
I’m not going to point out all the stars in the sky now but just a few of the more interesting and important ones used to find your way. Let’s have a go.
Wait for about an hour after sunset and then look to an azimuth of 270 degrees, so that’s west, I want you to look about 50 degrees up from the horizon. That’s about two outstretched hand spans and one clenched fist.
When you look into the sky everything appears to be the same unknown distance. In the past there some quaint ideas including that the stars were holes in a celestial sphere wrapped around the Earth. After the Copernican revolution that idea lost favour but it wasn’t until 1838 that the first distance to a star other than the Sun was calculated.
Now, as we understand the enormity of space we use the term ‘light year’, which is the distance that light travels in one year in the vacuum of space. Just how far is a light year? We know that light travels roughly 300,000 kilometres per second in the vacuum of space. Multiply that by 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 365.25 days per year, on average, and you’ll end up with something like 9,500 billion kilometres which is such a silly number we just don’t use it. It’s too big and too complicated even for relatively close stars.
The star that we’re trying to find is 25 light years and 1.8 times the diameter of the Sun. Think about that. You see it now as it was 25 years ago. Every time you look at stars you are looking back in time. This star is a young white star and one of the first stars to have had planets directly imaged orbiting it in 2008. It is the brightest star in the constellation of Piscis Austrinus, the Southern Fish and is called Fomalhaut.
To the ancient Mesopotamians perhaps as long as 5,000 years ago, this star along with three others, Aldebaran in Taurus, Regulus in Leo, Antares in Scorpius were used to signpost the solstices and equinoxes but not anymore.
Fomalhaut was, but no longer, the brightest star near the point in the sky that marked the Winter Solstice as seen from the Northern Hemisphere.
When you look at Fomalhaut, there are not many bright stars nearby. What I want you to do is try and see is an image of a fish, let your imagination go and you may just be able to see a simple fish if you play dot-to-dot. If not, how about one of those fabulous paisley swirls that were so popular in the 1960s. If you can see anything that looks like a paisley swirl with one bright star Fomalhaut at the chunky end of the swirl, then you are looking at the group of stars or constellation of Piscis Austrinus, the Southern Fish.
It is, incidentally, drinking the water flowing from the jug of Aquarius the Water Carrier but goodness me, that’s so hard to see.
Now that you’ve seen, though with some difficulty, Piscis Austrinus, look ever so slightly to your left, or the southwest. You will probably need a star map but try to look for a dot-to-dot long necked bird with trailing legs in flight.
Have I mentioned that you need a vivid imagination? Not easy is it but again with practice it does get a little easier. This particular group of stars is called Grus the Crane. It was created by Petrus Plancius, I don’t know if I’ve pronounced his name correctly, in the late 1500s. He was a famous Dutch astronomer.
I’ve challenged you with these two groups of stars because I want you to see straight away, they look nothing like the images we see in star atlases or on many star maps. You’ve got to use lots of imagination to change crude stick figures into more elaborate creatures that we see in our period drawings but don’t give up, it’s well worth a try and when you eventually do see some of these constellations, it’s one of those, “Ah ha, I can see it,” moments.
Roughly forty degrees, or two hand spans to the left of where we are, and about 60 degrees above the horizon, so that’s three hand spans up, you should be able to see the ninth brightest star in the night sky and the brightest star in the sixth largest constellation of Eridanus the River.
It is known as the end of the river or Achernar and it’s rather intriguing, because it’s about seven times the diameter of the Sun but spins 15 times faster at around 250km/s.
The effect of the rapid rotation is that the star flattens at the top and the bottom but bulges in the middle. Its equatorial diameter is about 50 percent greater than its polar diameter making it one of the flattest stars ever seen.
At a distance of 140 light years ago you see this star as it was 140 light years ago. You see everything in the sky as it was, not as it is.
From Achernar continue to your left and drop down to about 35 degrees altitude looking for another bright star. It’s actually the second brightest star in the night sky but its low altitude at the moment will dim it by about 50%. It is Canopus at about 310 light years, it’s 8.5 times the mass of the Sun and 70 times its diameter which makes it a pretty big star. At about 1,300 times the brightness of the Sun it is the brightest star within 700 light years of us. Yet as we look at it, it’s only the second brightest star in the night sky. I wonder why?
Canopus is a fairly famous. It was listed by the incredible astronomer Claudius Ptolemy in his Almagest around 150 AD. This whole region used to be part of a big constellation called Argo the ship that carried Jason and the Argonauts in search of the Golden Fleece. Over the years, astronomers thought it was too big, so they broke it up into four smaller constellations that we have now: Carina the Keel, Vela the Sails, Pyxis the Compass and Puppis the Deck.
Canopus is now regarded as the brightest star in Carina the Keel. The name itself probably dates back to the time of the Trojan Wars, and according to the poems and the stories of the time, it was the name of the ship’s captain. Fair enough, we have the ship in the sky, why not have the captain as well?
Continue to the east and look about 20 degrees above the horizon. What you should see is a twinkling display of the brightest star in the night sky. It won’t appear to be as bright as Canopus, which is higher up at this point in time, because being lower your looking through so much more of our protective and beautiful atmosphere.
It’s a lot closer, at only 8.6 light years away, making it the fifth closest visible star to us. It’s quite young at roughly 200 to 300 million years. Its size? Nearly twice as big and 25 times brighter than the Sun. While I’ve just mentioned a few numbers the main thing to note is, it’s close.
It’s nowhere near as big or bright as Canopus, but because it’s relatively bright and very close, it becomes the brightest star in the night sky as seen from anywhere on the Earth, and it is Sirius the Dog Star. It’s a beautiful star and historically incredibly important. Thousands of years ago, the Egyptians watched it very very carefully.
They’d see it disappear into the glare of the setting Sun and then for about 70 days it would not be visible. They’d then turn to the east and keep watch for it in the eastern sky in the early morning. When it first pops just ahead of the glare of the Sun, in something called heliacal rise, they were able to work out, on average, the length of the year, over many years of observation, to be 365 and a quarter days. Their error was just 11 minutes compared to the Tropical year that we use now and they did this thousands of years ago which is truly an amazing achievement.
Let’s continue around toward your left or toward the east north east and just 20 degrees above the horizon. Oh by the way, you may have noticed that we seem to be hugging close to the horizon. I’ll explain a bit more about that later.
Look for a red super giant. To most people, it’s not traffic light red or laser red, it’s orangish. Anything that you see in this part of the sky that is not white or blue you’re probably looking at it. It’s the tenth brightest star in the night sky, 1,100 times the diameter of the Sun. Goodness gracious me, that’s a huge object.
Think about that for a moment. This little twinkling point of light that you’re looking at in the east north east, roughly 20 degrees up, is 1,100 times the diameter of the Sun. Don’t forget, the Sun is 114 times the diameter of the Earth. You’re looking at something which is simply enormous! Its distance? In the order of about 640 light years. It’s more than 100,000 times brighter than the Sun… and it’s a dying star.
When you see a reddish looking star it can be one of two things. It’s either an incredibly long lived, in fact, you could almost say, immortal star, or it’s a short lived star at the end of its life as we see it. The thing is that the very small, almost immortal stars, well, none of those are visible to the naked eye. When you look around the night sky, every single star that you see that is orangish, reddish, is coming to the end of its life. They’re all dying.
We’re not exactly sure of the mass of this star but we know it’s fairly big. As a result, when it does die, it’s going to explode as a Type II supernova, pop!
When? Next Tuesday at two o’clock. No, we can’t predict it accurately but sometime within 100,000 to one million years or so. Who really knows? It would be really cool if it did explode during our lifetime because it’s relatively close and would be so spectacular to watch. However, let me assure you, it cannot possibly hurt us.
I haven’t told you its name yet, have I? This is one of the most unusual names in the sky. A long, long time ago, its Arabic name was something like ‘Ibt al Jauzah’ which means something like the Hand of the Big Man.
As a result of hundreds of years of mispronunciation the star Ibt al Jauzah is now commonly called…Betelgeuse. Yes, I’m sure you’ve heard of it before. Some people call it ‘Betelgeeze’, ‘Betelguzz’, or even just ‘Betelgeeurse’. They’re all wrong but they’ve become so common they’re all acceptable.
Betelgeuse is a dying star. Despite being the second brightest star in the constellation or group of stars known of Orion the Hunter it’s named quite often as the brightest, Alpha Orionis. Additionally, Australians tend to get the name of the constellation Orion wrong by calling it the saucepan.
You should have a lovely clear view of it now, looking toward the east north east. Find the orange glow of Betelgeuse, then go a little bit higher and you’ll see three stars in a row, close together of equal brightness, they make up the base of the saucepan.
If you can find it, you’ve done well. I should point out that it’s not Australians, in fact, our friends across the ditch in New Zealand often get it wrong as well, and so do many people in Southern Africa.
If you can, point some binoculars or a small telescope at the handle of the saucepan and narrow in on the middle star-like object of the handle. What you will see is a stellar maternity ward, the birthplace of stars and what you’re looking at is the beautiful object named M42. Oh, great, what a fabulous name. Astronomers like many other scientists love to catalogue objects. M42 means that it is the 42nd object in the catalog developed by a man whose name began with M, Charles Messier.
He made up a list of red herrings, things not to look at if you were trying to find a comet. This object was simply the 42nd object of his list. It is a nebula which is the Latin word for cloud. It’s a star forming cloud that’s roughly 1,300 light years away and its huge at 24 light years across. M42 is being lit up from within by at least 8 baby stars that we call the Trapezium.
Leaving Orion, our next stop is a little bit further around toward the northeast and just a little higher to 25 degrees above the horizon. We’re looking for the star Aldebaran in the constellation of Taurus the Bull. Here you’re going to see pretty much just another of these golden reddish stars. Again the colour tells us the star is coming to the end of its life.
It’s the 14th brightest star in the night sky at about 65 light, it’s exhausted most of its hydrogen fuel in its core and has expanded to about 44 times the size of the Sun, but only a little under twice its mass. It will continue to expand and die within a few million years at most.
Go a little bit further toward the north, your left and we’re still only 25 degrees above the horizon. You’re going to see a small group of young stars, an open cluster and most agree is the most spectacular of all. It’s called M45 or the Pleiades.
At 445 light years they’re not exactly close, but they’re very young, less than 150 million years old. They’re so cute. They’re baby stars that have just formed. When you look at pictures of M45 or the Pleiades online, you’ll actually notice that quite often it’s surrounded by a lovely bluish glow. That bluish dust cloud as it turns out is not part of the Pleiades itself. It’s between us and the stars. The two-dimensional view that we have is a little confusing at times.
There are many different cultural stories that relate to these stars as being seven sisters. If you look at them, however, you’ll probably be able to see six. If you’ve got really good eyesight, you might see nine. Rarely do you ever meet anyone who can say, “Well, do you know what? I can see seven.” Yet strangely, they’re often referred to as seven sisters.
By the way, if you drive a Japanese car and it has an emblem on the bonnet of a group of stars joined by lines, you’re looking at a Subaru. Yes, that’s the Japanese name for this group of stars.
To the ancient Greek, they represent the daughters of Atlas who carried the world upon his shoulders, his wife, Pleione, and their seven daughters. It’s well worth having a good look at. The Pleiades used to be their own constellation but for some time now, we consider them to be part of the larger Taurus the Bull.
Continue now towards the north and look for another zodiac constellation with an enormous number of stars. Let’s count them together. In terms of bright stars, we have one, two, three… and that’s it. It’s devoid of stars. So what can you make out of three stars? Apparently, Aries the goat that produced the Golden Fleece in the story of ‘Jason and Argonauts’. There’s not a whole lot to see here unfortunately, but it is a very famous constellation in terms of sky lore and astronomy.
The astronomical version of longitude used to start in this part of the sky in what we call it the First point in Aries. Sadly, it gets rather complicated here because the Earth does a 26,000 year wobble on its axis and everything changes position ever so slowly.
This first point of Aries is no longer in Aries but has moved on into the next constellation, Pisces, the Fish, and heading toward the constellation of Aquarius hence the 1960s song “The Dawning of the Age of Aquarius” though that’s a few hundred years away.
In my opinion, don’t waste too much time looking into Aries with only three bright stars. Continue past it and now head toward the northwest for a group of stars that’s fairly obvious and makes up a big square. What you’re looking for is the flying horse, Pegasus.
If you’re away from the city lights and there’s no Moon and you have a good view toward the northwest, because it is quite low, you should be able to see the body of the horse which of course is the big square. Look carefully at one of our star maps and you should be able to pick out the long neck and the face of the horse. It’s got two cute little front legs but sadly for a flying horse, what’s missing? The wings
The main reason in spending time trying to find Pegasus is that wrapped around it is a fairly faint dot-to-dot V-shape with a little bit of a loop at either end. Oh, goodness me that sounds a bit complicated and you will need your star map to be able to see this. The V-shape with the loop at either end represents Aphrodite and her son Eros, or if you like, Venus and Cupid. It is the constellation of Pisces, the Fish.
Continue past Pisces and we’re going to finish off as we look toward the west for the constellation of Capricornus, the Sea goat. It’s below Fomalhaut or the starting point but being the second faintest of the constellations it’s probably a bit too late for that.
I mentioned earlier that all we’ve done is a bit of a loop around the horizon, between no more than 30 and 60 degrees up. We haven’t looked directly overhead. Why not? At this time of year and this time of night the brightest part of our galaxy the Milky Way is sitting on the horizon.
The stuff that’s directly overhead now, such as Phoenix the Bird, which is one of the 12 constellations invented by Petrus Plancius in the 16th century, or Cetus the Sea Monster or some of the newer ones like Sculptor were introduced by Nicolas Louis de Lacaille in the 18th century. I’ve probably made a mess of his name but that’s the best I can do I’m sorry.
These constellations are in effect astronomical fillers. There’s not a whole lot up there to have a look at with the naked eye. So they’re there as a way of breaking the sky up into more manageable regions, a bit like outer suburbs of a big city. They are just some of the other constellations in the sky.
If you can get away from the bright glow of the city or towns and there’s no Moon in the sky, head back toward the south and you should be able to see the Large Cloud of Magellan and the Small Cloud of Magellan. These look like two fluffy bits of the Milky Way that have drifted off and broken away, a faint, wispy glow of light.
The Large Magellanic Cloud is an irregular galaxy with a central bar. It’s the third closest galaxy to us and at about a hundredth of the size of the Milky Way. There’s enough material in this galaxy to form about 10 billion stars the same as the Sun. At 160,000 light years, astronomically, it’s very, very close. It’s so close, that the Milky Way is stripping stars away from it in something called the Magellanic Stream.
Long, long ago, in the last millennium, 1987 in fact – goodness me, such a long time ago – this area of the sky was home to the first supernova, an exploding star, visible to the naked eye since 1604.
We’re desperate to see a star blow up in our galaxy the Milky Way but not too close of course. We haven’t seen one since the invention of the telescope more than 400 years ago and that’s just a little annoying.
The other small patch of light that you can see is the Small Magellanic Cloud. It has a mass of about seven billion times that of the Sun and is about 201,000 light years away.
Key events for December 2018.
New Moon is on Friday the 7th at 6:20pm Australian Eastern Daylight Time or AEDT.
The first quarter Moon is on Saturday the 15th at 10:49pm
Full Moon is on Sunday the 23rd at 4:49am
Last quarter Moon is on Saturday the 29th at 8:34pm
The Summer solstice, the point at which the Sun reaches its most southerly point in the sky, is at 9:23am on Saturday the 22nd of December.
This is also the longest day with the Sun above the horizon for 14 hours and 25 minutes in Sydney.
The best meteor shower of the year for us in the South is the Geminids, which peaks in the early mornings of the 14th and 15th and this year there may be a bonus but I’ll get to that shortly.
The First Quarter Moon will have no effect setting around midnight. So, if you are keen to make the effort to find a dark location away from the larger cities and towns, look north, sit down, make yourself comfortable and…wait. If you are patient I can almost guarantee you’ll see these tiny visitors burn up as they collide with our protective atmosphere at stunning speeds between 80 to 120km above us.
Our brilliant year of planets in the evening sky is coming to an end. Saturn is only visible for the first part of the month and on the 9th it will be close thin crescent Moon.
Mars, the Roman god of war that was so good earlier in the year is by now a small red dot wandering from the constellation of Aquarius to Pisces. On the 15th the First Quarter Moon is nearby in the north.
The morning sky is a little better. The fleet footed Mercury will run through three constellations, Libra, Scorpius and the 13th Zodiac Ophiuchus. On the 14th it will be very close to the planet Jupiter as we see it but you will need a very clear view to the east just ahead of sunrise.
Venus will dominate the eastern morning sky starting the month in Virgo before moving into Libra. On the 4th the crescent Moon will be to the north.
Now for the wildcard for the month and possibly the year. Many an astronomer has been scarred by talking up evil stars before they arrive. Evil stars I say? Yes, also known as hairy stars or universally now as comets. This month we may, and I do emphasise may, see a good comet in the north after sunset.
Comet 46P/Wirtanen was discovered in 1948 and this year in the first two and half weeks of December it might be visible to the naked eye from a dark location.
It does come past every 5.4 years but this year it comes closer than before or apparently well into the future.
On the 17th of December it will be just 11 million km from us but the waxing Moon will interfere to some degree until after the 23rd.
I think the viewing trick will be to balance the potential rapid brightening due to its close pass to the Sun on the 12th known as perihelion and the waxing moon. Up to the 15th the Moon will set before midnight and the comet will be reasonably high in the north to north west. Considering the Geminid meteor shower is around at the same time I would recommend an excursion to a dark safe northerly viewing vantage point.
As for the comet itself the nucleus is only 1200m across the coma or fuzzy bit around it may be hundreds of thousands of kilometers across. It will start the month in Cetus, then briefly move through Eridanus into Taurus around the 11th. At this point it should be easy to see above the group of stars called the Pleiades or M45 that I mentioned earlier. As the month proceeds check our Facebook page for up to date details. If you take any pictures please share them if you can, along with technical details on how you did it as many other people will love to try to do so as well. A DSLR mounted on a tripod at high ISO and between 10-30 seconds should show something.
The caveat of course is that trying to predict what a comet will do is a little like herding cats. It may therefore be a dud or it may be a beautiful ghostly apparition that changes position each night before heading over our northern horizon. Give it a go and let me know what you see.
If you would like more detailed sky maps – sunrise, sunset, Moon, and tidal times and a whole lot more astronomical information I recommend you buy the book ‘The Australasian Sky Guide’ by Dr Nick Lomb available from Sydney Observatory and Powerhouse Museum shop.
It’s only $16.95 if you come into our shops. There are additional postage charges if you order online. Our website at maas.museum has lots of up to date information on our astronomy blog and details about visiting Sydney Observatory to use our telescopes, see a program in our space theatre or visit the digital planetarium.
We have programs for all ages and you can also engage with us on Facebook by searching for Sydney Observatory or via Twitter @SydneyObs.
If you have any questions or feedback please don’t be shy, do share them with us and we’ll get back to you as soon as we can. My name is Geoffrey Wyatt. I’m one of the team from the Museum of Applied Arts and Sciences’ Sydney Observatory and I hope you’ve enjoyed this tour of the December night sky.