To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map or chart each month. This month’s guide is presented by Geoffrey Wyatt, Sydney Observatory’s Education Program Producer.
With the help of a clenched fist and a nice glass of wine, Geoffrey tours us through the December night sky and reveals just how many planets are visible this month. The answer may surprise you.
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See The Sky Chart
We provide a December 2017 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 traveler and I will help you on your journey through the night sky. 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 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 drop of Chardonnay for those old enough to enjoy it.
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 roughly 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 your 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. Outstretch fingers and thumb from pinkie-tip to thumb-tip you have 20 degrees. With a little practice you’ll be able to do it with ease.
Let’s have a go. Wait for 30 to 40 minutes after sunset and 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.
You’re looking for a star that’s only 25 light years away. 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 it’s too complicated.
We simply say that a light year is the distance that light travels in one year in the vacuum of space.
The star that we’re trying to find is 1.8 times the diameter of the sun. It’s a young white star and one of the first stars to have had planets directly imaged orbiting it. This was only done in 2008. This star is the brightest star in the constellation of Piscis Austrinus, the Southern Fish, and it’s 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 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 a bright star, Fomalhaut, at the chunky end of the swirl, then you are looking at the group 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.
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 many star maps. You’ve got to use your 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.
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 constellation of Eridanus the River.
The star is called Achernar and it’s rather intriguing, because it’s about seven times the diameter of the sun but spins 15 times faster.
The effect of the rapid rotation is that the star flattens at the top and the bottom but bulges in the middle. In fact, its equatorial diameter is about 50 percent greater than its polar diameter.
You’re also looking at this star as it really was 140 years ago. You’re looking back into time. That means that this star is at a distance of about 140 light years.
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 star. 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 considered 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?
What I like about this star is that the Boorong Indigenous community, a clan of the Wergaia language group in what is now known as Northwestern Victoria, see this star as a male crow by the name of Wah. Wah was the first entity to bring fire to the people and he is an Elder of the Nurrumbunguttia, the old spirits in the sky.
If you have a telescope or a pair of binoculars, this part of the sky, although it’s a bit low at the moment, is actually a beautiful region to scan. Not far away from the star Canopus or Wah, we have the intriguing object called Eta Carinae which contains a cataclysmic variable star a type of violent binary star system which last flared in the 1840s when it went from a fairly inconspicuous third or fourth magnitude background star to being the second brightest star in the night sky and then slowly fade from visibility.
The Boorong incorporated this star’s variability into their Dreamtime or oral traditions, which is really quite amazing. As a result, this star became known as Collowgullouric Wah, which means the wife of the star Wah or Canopus.
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 object, 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.
I’d like to point out that to the Boorong clan, it is Warepil a male eagle, and again, an elder of the Nurrumbunguttia, the old spirits. Every community around this beautiful land has incredible stories and knowledge about the night sky and I encourage you to learn from them where possible but remember to treat the stories with respect as they are quite probably the oldest on the planet!
Let’s continue around toward your left or towards 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 fairly close to the horizon. I’ll explain a bit more about that later on.
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, 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, actually, 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 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 is actually named quite often as the brightest, Alpha Orionis. Additionally, Australians tend to get the name of Orion wrong by calling it the saucepan.
You should have a lovely clear view of it at the moment, 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. You can go up one side, up the other side, and then off at an angle for the handle, and there you have it.
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 onto 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 simply 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 particular 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. It’s absolutely huge at 24 light years across. It’s part of a much larger cloud that you can’t see all of unless you do incredibly difficult astrophotography. The whole cloud is called the Orion Molecular Cloud. This portion of the cloud of gas and dust that we can see is being lit up from within by at least 8 baby stars and we call them the Trapezium. If you have a look, you might just be able to see a few of them in there. We believe that there’s enough material to form around 700 stars at the moment. Six of them, however you can see relatively easily.
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.
Thousands of years ago from Mesopotamia, Aldebaran in the constellation of Taurus was the brightest star near the Vernal Equinox. The Vernal equinox is the point in the sky where the Sun moves, as we see it, from the Southern Hemisphere into the Northern Hemisphere marking the beginning of the northern spring. This was also used to signal the start of the New Year in March. The idea of starting the year on the first of January, was trialed a few thousand years ago but fell out of fashion especially during the Middle Ages. It’s only been since the Gregorian reform that it once again reverted to the first of January. England and its colonies only changed back to the first of January in 1752.
Taurus with its bright star Aldebaran is perhaps the oldest of all the 88 constellations that we now officially recognise. It’s a very important creature. A bull is not only a food source for many of us, it’s a beast of burden and many people depended on them. It’s therefore not surprising that this animal worked its way into sky lore.
In one story it’s actually the king of the gods, Zeus or Jupiter, carrying his lover, the beautiful young woman Europa off to the island of Crete. This was such a famous story from long ago, that the entire continent of Europe took her name.
Aldebaran, brightest star in Taurus is what we call a K5 orange giant. It’s the 14th brightest star in the night sky at a distance of about 65 light years and it’s coming to the end of its life. At the moment, 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 have a 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 it of a group of stars joined by lines you’re probably looking at a Subaru. Yes, that’s the Japanese name for this group of stars, Subaru.
These stars to the ancient Greek represent Atlas who carried the world upon his shoulders, his wife, Pleione, and their seven daughters. It’s well worth a look. 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 fairly devoid of stars. What can you make out of a group of just three stars?
Aries, the goat that produced the Golden Fleece that’s so famous 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 starts 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 over 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 makes up a 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 definitely 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 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.
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 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.
The Large Magellanic Cloud is actually a rather spectacular object to have a look at. With a small telescope you’ll be able to see one of the largest nebulae that we’ve seen, called the Tarantula Nebula. Once again, “nebula” is just Latin for cloud. It’s a very rich star forming region and well worth a look.
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, 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 2017
Full Moon is on Monday the 4th at 2:47am
Last quarter Moon is on Sunday the 10th at 6:51pm
New Moon is on Monday the 18th at 5:30pm
The first quarter Moon is on Tuesday the 26th at 8:20pm Australian Eastern Daylight Time or AEDT.
The Summer solstice, the point at which the Sun reaches its most southerly point in the sky, is at 3:28am on Friday the 22nd of December.
This is also the longest day with the Sun above the horizon for 14 hours and 25 minutes in Sydney.
Many people assume that the longest day is the day on which we have the earliest sunrise and the latest sunset for the year. Some even get upset and write letters to the newspapers when they discover that that is not the case. The earliest sunrise is in early December while the latest sunset doesn’t actually occur until early January and that is the result of our non-circular orbit around the Sun and the tilt of 23.5 degrees caused by an impact perhaps as long as 4 billion years ago, cool huh?
The best meteor shower of the year for us in the South is the Geminids, which peaks on the 14th and 15th. The waning crescent Moon should have little effect so make the effort to find a dark location looking north, sit down and 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.
The evening sky in December is in effect: planetless. Saturn and Mercury in Sagittarius set shortly after the Sun within the first few days of the month. By the middle of the month Mercury sets before the Sun and Saturn 20 minutes later. Oh dear no planets in the December night sky.
The morning sky is a little better. The fleet footed Mercury will appear in the 13th Zodiac Ophiuchus just below Scorpius low in the east by the end of the month.
Mars is low in the east in Virgo at the start of the month before drifting back to Libra and a close approach to Jupiter late in December and early January. It’s well worth looking at Mars and noting how bright it is throughout December, why? Well, next year in July, Mars will be the brightest it has been since 2003 and for about another 15 years but you’ll have to wait until next year for more information about the 2018 Opposition of Mars and an incredibly rare event. Whatever your plans for next July make sure you’re ready for a super early morning of viewing on 28 July 2018 as it will be a once in a lifetime opportunity! Make sure you follow us for more details.
On the 14th of December the waning crescent Moon will be below Mars and to the left of Jupiter. By the 15th the Moon will be closer to Jupiter just below it in Libra.
If you want more detailed sky maps – sunrise, sunset, Moon, and tidal times and a whole lot more astronomical information I recommend you purchase the book ‘The Australasian Sky Guide’ by Dr Nick Lomb available from Sydney Observatory and Powerhouse Museum shops. 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 look through our wonderful telescopes and see a program in the digital planetarium.
This is Geoffrey Wyatt. I’m one of the team from the MAAS’ Sydney Observatory and I hope you’ve enjoyed this tour of the December night sky.