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, Astronomy Educator at Sydney Observatory (pictured at right).
In the December sky guide, Geoff tells us how the ancients of Mesopotamia used the stars to help them as a form of calendar markers, and how Indigenous Australians incorporated the stars into their Dreamtime stories. As well as guiding you to find the two brightest stars in the night sky, Sirius and Canopus, Geoff tells us our best chance in December to see the Geminid meteor shower is on the mornings of 14 and 15 December.
For this and more, listen to the December 2013 night sky guide audio, or read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a starmapDec2013 (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.
BUY THE BOOK
Our annual book, ‘The 2014 Australasian sky guide’ by Dr Nick Lomb has more information and star maps for months from December 2013 until December 2014 inclusive, plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information. You can purchase it ($16.95) at Sydney Observatory and Powerhouse Museum shops or other good bookshops, or online through Powerhouse Publishing (additional packing/postage costs apply).
READ THE TRANSCRIPT (after the jump)
Transcript of the December 2013 monthly sky guide audio
Hello, this is Geoffrey Wyatt, Senior Astronomy Educator here at Sydney Observatory. I’m going to talk to you about what’s in the sky for the tenth month of the old Roman calendar, before the reform of Julius Caesar in 46 BC. Tenth month, December? Yes, that’s right. Of course, things were changed around a little bit and December became the twelfth month. So we’re on target, but of course you’ve probably wondered like I have, why December is twelfth. But anyway, let’s move along.
To have a look at the night sky, you’re going to need some resources. One of those will be a monthly sky guide map or a copy of the Australasian sky guide by Dr Nick Lomb. You’ll also need a very clear view of the sky. To be honest, you can only get to what you can get to, but the higher you are, the clearer the view you have of the four cardinal directions north, east, south, west, away from lights, away from trees and buildings the better the view.
Of course, at this time of the year it should be quite nice outside. So, a nice comfortable blanket to sit on as well and perhaps a drop of Chardonnay for those of us old enough to enjoy it. That will assist, to some extent, your imagination when coming to looking at the stars.
What we want you to do is wait until just after sunset, get a clear view, and I want you to look to a part of the sky that is 23 degrees right ascension and 30 degree declination. Have you got it yet? Hmm?
Of course, that raises a problem. Most people don’t know what right ascension and declination are. That’s, if you like, the astronomer’s version of longitude and latitude. It’s a pretty hard way of finding your way around as well, so we need some other way to find our direction.
Most of us know our cardinal directions. North, east, south and west with the Sun roughly setting over in the west depending on the time of year, roughly rising in the east and we can figure out north and south. So we can find our direction around from the north in something we call azimuth by looking in that direction, so 90 degrees azimuth would be east, 180 would be south, 270 is west and so on. That part is easy.
If I were to say to you, ‘Something is directly overhead’, I think most people could figure out that that’s 90 degrees up or halfway, 45 degrees. But when it comes to other angles, it’s intriguing how poorly we do at estimating angles.
What I want you to do, therefore, is to hold out your hand at arm’s length, clench your fist and hold up your pinkie. Now, for most people, regardless of your age and size because the proportions are all pretty much the same, your pinkie at arm’s length will cover roughly one degree of the sky or if you like, twice the size of the full Moon. Close the finger in and make a clenched fist and you’ve got a marker for roughly ten degrees. Now stretch out your fingers to your thumb and you’ve got roughly 20 degrees.
Now that we have a way of finding objects in the sky by measuring angles east of north and degrees above the horizon, I want you to go to an azimuth of 270 degrees. That’s west. I want you to look about 60 degrees up from the western horizon, so 60 degrees will be three outstretched hand spans from pinkie to thumb.
What you’re going to look for is the fourth of the four Royal Stars. People have been looking at the stars for many, many thousands of years. Of course later on, I’ll talk about some indigenous stories and indigenous people of this land have been looking at the stars, we think, longer than any other community on the planet which is really something we should all be proud of.
But for the time being, we’re going to look at one of the four Royal Stars as was determined by the people living in Mesopotamia, the region between the Tigris and the Euphrates as many as 5,000 years ago. You’re going to look for a star that’s only 25 light years away. A light year is simply the distance that light travels in one year which is a long way.
Light travels, for example, in a vacuum of space at roughly 300,000 kilometers per second. You multiply that by 60 seconds per minute, 60 minutes per hour, 24 hours per day and 365 and a quarter days on average per year and you end up with something like 9,500 billion kilometers which is such a silly number, we just don’t use it. It’s too complicated. So a light‑year is the distance that travels in one year.
So this star, 1.8 times the diameter of the Sun, is a young white star and is in fact one of the first stars to have had planets directly imaged in orbit around it and that was only done in 2008. So this star is the brightest star in the constellation of Piscis Austrinus, the southern fish. It is Fomalhaut.
The ancients that I mentioned a moment ago from Mesopotamia used stars, as have most people throughout the ages, as a form of calendar marker, and they plotted the position of four key events in the sky and they are the equinoxes and the solstice. They used the stars Aldebaran in Taurus, Regulus in Leo, Antares in Scorpius and Fomalhaut as we see it in Piscis Austrinus to mark these key points.
So Fomalhaut, thousands of years ago, but very importantly, no longer, was the nearest bright star, next to the winter solstice.
When you look at Fomalhaut, as I mentioned, there’s not many bright stars nearby. Try and see a fish, maybe you can, maybe you can’t, but let your imagination go wild and if you’ve had some of that chardonnay or red wine that I mentioned earlier, this may, in fact, assist just a little.
I want you to look for a paisley swirl of stars. Whoever thought that paisley would be of such significance to be related to something in the sky. But that wonderful fashion from the ’60s that occasionally comes back, you want to look for that paisley swirl right around the bright star of Fomalhaut and you just may be on the right part of the sky. This should be relatively easy, because as I mentioned, Fomalhaut is a bright star and there’s not much else in that region.
Once you’ve found Fomalhaut, which is incidentally drinking the water, flowing from the jug of Aquarius the Water Carrier – boy, is that hard to see – but what I want you to do now is move ever so slightly to your left or the southwest, as we’re looking at it. You’ve got to use your map that you’ve hopefully printed off as well, and you’re going to look for a long‑necked bird with trailing legs.
This particular constellation or group of stars is simply Grus the Crane, who was created by Petrus Plancius in the late 1500s. He was, of course, a fairly famous Dutch Astronomer. When you look at the paisley swirl which is supposed to be the fish, Piscis Austrinus, and Grus the Crane, you’ll see straight away that ‑‑ ooh, these pictures look nothing like what you see in star atlases and some of the wonderful pictures we see in books and on the web.
But they don’t, you’ve got to use your imagination and you can make out some simple stick figures if you’re good at it. Don’t give up, it’s well worth a try and when you do eventually see one, it’s one of those, ‘Ah, I can see it!’ moments.
Fourty 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 called Achernar.
Achernar is rather intriguing, you see, because it’s about eight times the diameter of the Sun, but it spins 15 times faster than the Sun. The effect of that rapid rotation is the star flattens at the top and bulges in the middle.
In fact, its equatorial diameter is about 50 percent greater than its polar diameter. So it is, if you like, somewhat squashed. But by the way, if you look at the distances, you’re looking at this star tonight as it really was about 144 years ago. You’re looking back into time, and of course, that means that the star has a distance of 144 light years.
Some Indigenous cultures of Australia use Achernar and consider the nearby second brightest star in the night sky, Canopus, to represent the cooking fires of two celestial brothers. The brothers, themselves, are represented by the Large and Small Magellanic Clouds at a distance of 160,000 light years and 201,000 light years away, respectively. They are, of course, two of our closest but not the closest galaxies to us.
Achernar is also quite intriguing because it’s on the opposite side of the south celestial pole. From the smallest of all 88 constellations and some of us here in the south would argue the most important of all 88 constellations, and that is the Southern Cross. Unfortunately the Southern Cross is not easy to see at the moment and you’d have to wait to about 3:00 AM to see it that low in the south-east.
And you can use the Southern Cross, drawing a line through the long axis, going all the way across the sky towards Achernar, then going back along that same line midway, and that’s pretty close to the south celestial pole. It’s not dead accurate, but it’s close enough.
As we drop down from Achernar, and head toward that second brightest star in the night sky, Canopus, we’re going to pass a couple of fairly important constellations. Well, really, they’re only important because this time of year when you can’t see the real Southern Cross, people often get confused by what we call asterisms.
Patterns of stars that look like pictures that aren’t actually part of a constellation, or not their own constellation, if you’d like. The asterisms that we’re going to mention are the False Cross and the Diamond Cross. They’re actually made up of stars from the two constellations of Carina the Keel and Vela the Sails.
You see, people look for the Southern Cross at this time of the year. It’s a nice time to be outside. The temperature is just right, in fact, we’ve got some lovely warm evenings. You look up for the Southern Cross and oops, not there.
What is there, of course, amongst the two to three thousand stars that you can see with the naked eye are four stars that make up a cross. Unfortunately, in this part of the sky, we see two false crosses. One of them actually called the False Cross, the other, the Diamond Cross. Both are larger and fainter than the real Southern Cross, and nor do they have the two bright pointers that point toward it.
As we go past the false crosses, we’re going to look for the second brightest star in the night sky, and that’s Canopus. Canopus is the southeast. It’s about 50 degrees above the horizons, so that’s two hand spans and one clenched fist in the southeast.
Here we have a star that’s 310 light years away, it’s 8.5 times the mass of the Sun. That’s a pretty big star. That means that it’s actually about 1,300 times brighter than the Sun and that actually makes it the brightest star within 700 light years of the Sun. Yet, as we look at it, it appears to be only the second brightest star in the night sky. I wonder why. I don’t know. Not only is the star’s intrinsic brightness important, it must be its distance as well.
There’s another star we’ll come to shortly which is not as bright, but because it’s close, looks brighter. But I’ll come back to that in just a moment. Canopus is a very famous star. It was listed by the incredible astronomer, Claudius Ptolemy, in his Almagest of around about 150 AD.
Not only is it the second brightest star in the night sky, it’s famous because it’s been around for a long time. Now this whole region of the sky used to be part of a really, really big constellation called Argo, the ship that carried Jason and the Argonauts in search of the Golden Fleece.
But over the years, astronomers actually thought it was too big, so they broke it up into four smaller constellations. We now have Carina the Keel, Vela the Sails, Pyxis the Compass, and Puppis the Deck.
Well, the brightest star in Carina the Keel is Canopus. The name, itself, probably dates back to the time of the Trojan Wars and, according to the story, it was the name of ship’s captain, so Argo the ship, its captain’s name was Canopus. Fair enough, he gets his own star, I suppose.
What’s intriguing about this star, too, is that the Boorong Indigenous Community, a Clan of the Wergaia Language Group in Victoria, see this star as a male crow by the name of Wah. Wah was the first entity to bring fire to the people.
If you’ve got a telescope or a small pair of binoculars, this part of the sky, although it’s a bit low, is actually quite a beautiful region to scan. Not too far from the star Canopis or Wah, we have a very intriguing object called Eta Carinae which is a cataclysmic variable star. It’s a really bizarre object.
The historian, Stanbridge, has recorded that the Indigenous people I have mentioned, the Boorong, actually recorded, if you like, the outburst of this star in 1843. You see, in the 1800s it went from being a fairly inconspicuous third and fourth magnitude star which means it’s just one of the background mob, to suddenly become the second brightest star by 1843 and then slowly fade away from visibility.
Now, it seems the Boorong actually incorporated this star’s variability into their Dreamtime stories or their oral traditions which is really quite amazing. As a result, this star has a name and that is Collowgullouric Wah, which simply means the wife of the star, Wah.
What we do after we’ve had a look at this region in the sky around Canopus is go toward the east and we’re going to look about 20 degrees above the eastern horizon. What you should see is a twinkling dazzling display of the brightest star in the night sky.
It may not appear to be as bright as Canopus which is higher up at this point in time, because this star is a little bit lower. It’s a lot closer at only 8.6 light years away making it the fifth closest star to us. It’s quite young, too, at only 200 to 300 million years. Its size, well, a little bigger than the Sun’s. So nearly twice as big and nearly 25 times brighter.
There’s a few numbers there, but the important thing is that this star is close, it’s 8.6 light years away. It’s nowhere near as bright as Canopus that we’ve just had a look at, but it’s so much closer, and as a result, this star, Sirius the Dog Star, is the brightest star in the night sky seen anywhere on the Earth.
It is a beautiful object and historically incredibly important. You see, thousands of years ago, the ancient Egyptians used to watch this star disappear into the glare of the Sun for about 70 days. Then, they would keep watch for it in the morning eastern sky.
When they saw it just pop up out of the glare of the Sun, in the morning, they were able to use that to work out over a long period of time the length of the year was 365 and a quarter days. Their error was just 11 minutes and they did this many thousands of years ago. A really quite incredible thing to have done.
So Sirius is beautiful, it’s also useful to work out, for example, the time of the year. I should point out too that again to the Boorong Clan, it actually represents the star, Warepil, and that was a male eagle and he was one of the chiefs of the Nurrumbunguttias or the old spirits.
To other Indigenous communities, the appearance of Sirius marked the time of the year when it was the right time to go looking for tasty young dingo pups. Oh, well.
That highlights something quite important. The stars have been used for thousands of years in Australia and around the rest of the word as a form of calendar marker and as a way of navigation.
Let’s continue around towards our left, or towards the north-east, and just 20 degrees above the horizon. By the way, have you noticed that we seem to be hugging the horizon a fair bit here? I’ll explain why later.
Just 20 degrees above the horizon is a fairly bright orange‑looking star. We call it a red supergiant, but to most people it’s not traffic‑light red or laser red. It’s orange‑ish. Anything you see over in this part of the sky that’s not white or blue, you’re probably looking at it. It’s the eighth brightest star in the night sky. It’s 1,100 times the diameter of the Sun. Goodness gracious me.
Think about that for a moment. This little twinkling point of light that you’re looking at in the northeast, 20 degrees up, is 1,100 times the diameter of the Sun. The Sun is 114 times the diameter of the Earth. You are looking at something that is enormously big. Its distance? In the order of 430 light years. It’s 100,000 times brighter than the Sun. Goodness gracious me. What is it?
It’s a dying star. Whenever you see a reddish‑looking star, it’s one of two things. It’s either an incredibly long‑lived…in fact, you’d almost say immortal star. Or it’s a very short‑lived, dying star as we look at it. The thing is, these very small, almost immortal stars, none of those are visible to the naked eye. When you look around the night sky, every single star that you see that is golden orange reddish is actually dying, and coming quite close to the end of its life. Obviously, if it’s dying.
This particular one, its mass we’re not sure of. As a result, we’re not exactly sure what’s going to happen. But quite probably, [makes popping sound] it’s going to explode as a type II supernova. When? Well, next Tuesday at 2 o’clock. No. Actually, we have no idea. It could be within the next 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.
I haven’t told you its name. This star has one of the most intriguing names in the night sky. A long, long, long time ago, its Arabic name was Ibt al Jauzah, or something along that pronunciation, meaning the hand of the big man’. Hand of the big man? Yeah. It’s an unusual name. It’s so difficult to pronounce.
What’s happened is, over the years, as this name has come to us from different Arabic communities in the Middle East, it’s gone to the ancient Egyptians and then to the Greeks. Then, of course, there was this rather unfortunate period called the Dark Ages, when so much wonderful heritage from the past was lost.
Then, of course, there was the awakening, the Renaissance. People suddenly started to discover translations of a copy of a translation of a copy. We had all these strange star names. As a result, many of them over the years have been mispronounced. They’ve devolved, I suppose you could say. As a result, Ibt al Jauzah is now commonly called Betelgeuse.
Yes, I’m sure you’ve heard of it before. Some people call it ‘Beetle-goose’ or ‘Beetle-geez’, but ‘Beetle-juice’ is just as wrong and therefore just as acceptable as all the other names we have for it. It is an enormous, dying star in one of the more famous constellations, that is, Orion the hunter.
Australians are quite unique at getting the name of Orion wrong. We should be looking towards the east. We should have a lovely clear view of it at the moment. What you’re going to look for is a group of stars that looks like a saucepan. Look for three stars not far from the orange glow of Betelgeuse. In fact, it will be a little bit higher. Three stars that make up the base of the saucepan. You can go up one side and, of course, you can go back up the other side. Three more star-like objects that form a handle.
If you can find that, you’ve done well. It is typically only Australians and our friends across in New Zealand and in Southern Africa that refer to this group of stars as looking like a saucepan. You see, it’s been named from the northern hemisphere long ago. As a result it, it didn’t look anything like a saucepan but, in fact, the mighty hunter, Orion.
There are different stories about Orion. You can just imagine. If you were to pass on a secret to your friend and then a relative, and then have them pass it on and pass it on and pass it on, within a few hours you’d probably get a different story, so you can imagine what’s happened over thousands of years. There are many conflicting, odd stories about some of the patterns we have in the sky.
One of the ones I like is that Orion was a mighty hunter, one of the mightiest hunters ever to have lived. As a result, he used to hang around with the goddess of the hunt. Her name was Artemis. Straightaway, we’re talking about a story from ancient Greece.
Orion made a very foolish mistake. He boasted that he could kill any animal on the planet. After all, he was a hunter. To teach him a lesson, Artemis created the giant scorpion, Scorpius, to go into battle with him. The battle that followed was so incredible that it even caught the attention of Zeus himself, king of the gods. Ultimately, Orion was stung and killed by the scorpion. Zeus took the scorpion and placed him in the sky.
Artemis, with a tinge of regret, took the body of Orion and placed him into the sky, as well. It’s also a bit a reminder for mere mortals to curb their ambitions. She placed him into the sky on the opposite side of the sky from Scorpius so that you don’t ever get to see the two close together. Coming up in the east right now we see Orion, which gives you a hint that Scorpius has just disappeared from view over in the west.
It’s a fabulous constellation. I think most people at some stage or another have been able to look at it. The problem is, as I’ve mentioned also, in the southern hemisphere it’s upside down, so we look at it and see a saucepan, not the mighty hunter Orion.
Before I go, some other stories have suggested that Orion was ‑‑ well, how can I put it? ‑‑ somewhat dim. He’s standing on a rabbit called Lepus the Hare. How good a hunter can he be if he’s standing on a rabbit and chasing a flock of doves in the form of the Pleiades nearby? Not exactly a big‑game hunter. Again, there are different stories.
Go back to that saucepan, as we’ve described it, and have a look at the handle of the saucepan. You may remember, just a moment ago I said, ‘Three star-like objects’. The middle star-like object of the handle is not a star at all. In fact, I suppose you could call it the maternity ward. What you are looking at is the birthplace of stars. This is truly an amazing sight, even through a small telescope. A pair of binoculars might be pushing it, but if you can get to a small telescope, please have a look.
You’re looking at an object which is absolutely beautiful. It’s name? M42. Right. Remember that astronomers don’t typically have wonderful imaginations these days. It’s simply a catalog name. It means it’s the 42nd object in a catalog developed by a man whose name began with M ‑‑ Charles Messier, a Frenchman. He made up a list of ‘red herrings’ ‑‑ things not to look at if you’re trying to find a comet. This particular object was the 42nd in his catalog.
What it is is a nebula. ‘Nebula’ is, of course, the Latin word for ‘cloud’. It’s a star cloud, a star‑forming cloud that’s roughly 1,300 light years away. It’s absolutely huge. It’s about 24 light years across. It’s a very, very large object In fact, it’s part of a much larger object called the Orion molecular gas cloud, but you can’t see all of that unless you do super-long astrophotography, which is ridiculously hard, in my opinion.
This cloud of gas and dust is being lit up from within by at least six baby stars. We call this group of stars the Trapezium. If you can have a look, look for this glowing cloud, which is the middle star-like object of the handle. If you’ve got a slightly more powerful telescope, you’ll be looking at six little stars clustered together. There’s actually enough mass there to form…at the moment, we think about 700 are being formed in there right now, but you can see six with a relatively small telescope.
Our next stop in the night sky is a little bit further around towards the northeast and, again, just 25 degrees above the horizon. We’re going to look for the star Aldebaran in the constellation of Taurus the Bull. From here, you’re going to see pretty much just another one of these golden reddish stars. That tells us…what did I mention before? Yes, that’s right. The star is dying. Also, this star is the first of the four Royal Stars.
The Royal Stars, quickly. They were simply calendar markers, the brightest stars next to particular events in the sky. Many thousands of years ago from Mesopotamia, Aldebaran in the constellation of Taurus the Bull was the brightest star next to the vernal equinox, that is, where the Sun crossed from the southern hemisphere into the northern hemisphere, crossing the celestial equator, and marked the beginning of spring. That’s actually when the year used to begin.
This idea of starting the year on the first of January. That’s only a Johnny-come-lately sort of idea. For a long, long time, the year used to begin with the vernal equinox in March.
Taurus, Aldebaran. What you’re looking at is, as I’ve mentioned, probably the oldest of all 88 constellations because that’s where the Zodiac, the circle of the animals began, as seen from Mesopotamia. Taurus is, of course, a very important creature. The Bull not only is a source of food for many of us. It’s also a beast of burden. So it’s not surprising that this animal worked its way into sky mythology.
Let me warn you, however. You should never actually approach Taurus the Bull because in one of the stories it’s actually the king of the gods, Jupiter or Zeus, carrying his lover, the beautiful young girl, Europa, off to the island of Crete. This was such a famous story of Jupiter and Europa that the continent of Europe took her name. Cool, huh?
Aldebaran is what we call a K5 orange giant. It’s the 13th brightest star in the night sky. It’s about 65 light years away. It’s coming to the end of its life, as I’ve mentioned. At the moment, it’s exhausted all the hydrogen fuel in its core. It’s expanded and expanded and expanded. At this point, it’s about 44 times the size of the Sun, but only a little under twice its mass.
Think about that for a second. Something that’s only about twice the mass of the Sun, which remember is 114 times the size of the Earth, but 44 times the size of the Sun. The density of this star near the edges, near the outer areas, would be astoundingly low. Nonetheless it glows ‑‑ cool as far as stars are concerned ‑‑ an orange-reddish colour.
The star Aldebaran at 65 light years away is actually between us and a group of young stars in the background that make up that V‑shape I mentioned a little while ago. The V-shape group of stars is an example of something called an open cluster. This particular open cluster, called the Hyades is just 153 light years away, and that actually makes it the closest cluster to us. The stars are quite young at only about 625 million years.
Once you’ve found Aldebaran and the V-shape group of stars, we go a little bit further towards the north. We’re looking about 25 degrees up from the horizon. You’re going to see a group of young stars. In fact, this is another example of an open cluster. But this one, I think most people would agree, is the most spectacular of all.
It’s called M45. Here we go with that terrible M catalog again, but oh well. It works, so we keep using it. The 45th object in the catalog developed by Charles Messier is what we’re looking at, at the moment. But it also has other names. For example, the Pleiades.
To some Indigenous groups, for example the Maralinga area of South Australia, the story that relates to this is one of my favourites in the sky, and that’s the Woode Gooth-Tha Rra and the Minma-Birnee. The Pleiades or the the Woode Gooth-Tha Rra and the Minma-Birnee are about 445 light years away. So they’re not exactly close, but they’re less than 150 million years old. They’re so cute! They are baby stars that are just being formed. I suppose in human terms it’s like I’m going to visit them in the maternity ward at the hospital.
When you look at some pictures of this online if you do search for M45 or Pleiades, you’ll actually see a cluster of stars surrounded by a lovely bluish glow. That blue dust cloud as it turns out is not actually part of the higher Pleiades, it’s actually between us and those stars so you’re looking at two objects which can be a little confusing.
The other thing is the Pleiades are known as the Seven Sisters. What’s intriguing is this idea of seven sisters seems repeat itself right around the world. There are many different cultural stories that relate to these stars as being seven sisters including as I’ve mentioned the the Woode Gooth-Tha Rra and the Minma-Birnee. The thing is if you look at them however, you’ll probably only be able to see six. If you’ve got really good eyesight, you’ll might see nine. Rarely do you ever meet anyone who says, ‘I can see seven,’ but that’s what they’re called the Seven Sisters.
By the way, you also know their Japanese name especially those of you who drive a Subaru. If you’re a Subaru driver, have a look at that emblem on the front of your car. It’s a group of stars. Which stars? These, the Pleiades. Which also according to the ancient Greeks represent the daughters of Atlas who carried the world upon his shoulders and their mother Pleione. It’s a beautiful group of stars and well worth locating.
Once we’ve had a look at the Pleiades, which actually in its own right was its own constellation until relatively recently when it was demoted and simply became part of Taurus the Bull, we’re going to continue around to the north to look at a zodiac constellation with an enormous number of stars. Let’s count them ‑‑ one, two, three. Yes it’s fairly devoid of stars. What can you make out of three stars? In fact, the horns of Aries the Goat.
Aries the Goat is the goat who 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 fairly famous constellation because in astronomical terms we use our measurement position, our celestial equivalent of longitude, as having started in this part of the sky and we call it the first point of Aries.
Unfortunately it gets really complicated here because the Earth does a 26,000 wobble on its axis and that sort changes the position and orientation of objects in the sky. So the first point of Aries, if you like the zero starting point for our celestial longitude which we call right assentation, is actually no longer in Aries but is now over in Pieces and heading towards Aquarius.
If I could sing, I would burst into song and sing the song ‘The Dawning of the Age of Aquarius’. But trust me, you can listen to me on a podcast but you cannot listen to me sing. The point is that this celestial starting point for our measuring of positions is called the first point of Aries because thousands of years ago it was here, but it’s now drifted from Aries, to Pieces and in another couple of hundred years ‑‑ so not soon ‑‑ it will be in Aquarius.
In my opinion, don’t waste too much time looking at Aries with only three bright stars. Continue past it and look towards the northwest and look for a group of stars, four stars, that make 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’ve got a good view of it before it gets too low, you’ll actually be able to see the body of the horse which of course is the big square. Look carefully using 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 more importantly for a flying horse, what’s missing? Well, I can’t see any wings and it doesn’t appear to have any tail or rear legs either. But anyway, you’ve got the front half of a horse with a fairly chunky square body. It’s relatively easy to see as long as you’ve got a clear view.
But the reason we spent a bit of time on this one is just above and if you like wrapped around that square is a large V-shaped group of stars that are quite faint. Of course they’re another one of these water signs, star signs if you like, constellations in the part of the sky called the Sea. You’re looking for a V-shaped group of stars. It’s much bigger than the V I mentioned towards the Bull.
But at the either end of the V there’s a little circular or knobby loop of stars. What’s your looking at there are the gods Aphrodite and Eros. If you like, Venus and Cupid, in the constellation of Pisces the Fish.
We’re going to finish off as we head off towards the west and look at the constellation of Capricornus. It’s the Sea Goat, just below Fomalhaut. Now look, to be honest, at this time of the year it’s pretty hard to see because it’s not very bright. It’s the second faintest of all the Zodiac constellations and it’s only about 30 degrees up.
Hmm, I mentioned earlier, we’ve sort of done a bit of a loop around the horizon, between 30 and 50 degrees up. We haven’t actually looked directly overhead. Well, why not? Because at this time of the year, all the interesting stuff hangs around the edge, if you like. The periphery of Via Lactea, the Milky Way, is around the horizon.
The stuff that’s directly overhead, 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 the Sculptor was introduced by Nicolas Louis de Lacaille in the 18th century. These constellations are in effect astronomical fillers. There’s not a whole lot to have a look at up there with the naked eye. They’re just ways, if you like, of breaking the sky up into more manageable areas.
So all the action that we’ve just been talking about is in that band about 40 to 60 degrees above the horizon.
However, what you can see, away from the city and with no Moon in the sky, back towards the south you should be able to see the Large Magellanic Cloud and the Small Magellanic Cloud. They look like two small fluffy bits of Milky Way that have drifted off and broken away, sort of a faint, wispy glowing light.
The Large Magellanic Cloud is an irregular galaxy with a central bar. That just tells us it’s a galaxy. It’s the third closest galaxy to us and about a hundredth of the size of the Milky Way. There’s enough material in this to form about 10 billion stars the same as the Sun. It’s about 160,000 light years away, so that’s a pretty big distance for you and I. Astronomically, it’s right on top of us.
In fact, astronomically, our galaxy, the Milky Way is the local bully on the block and is stripping this galaxy of its own stars. There is a stream of stars going from the Large Magellanic Cloud towards us called the Magellanic Stream. So we are in effect ripping it apart or absorbing it. It’s going to collide with us in the very distant future.
If you’ve got a pair of binoculars or a small telescope, the Large Magellanic Cloud is actually a really spectacular object to have a look at. You’ll be able to see one of the largest nebulae that we’ve ever seen, called the Tarantula Nebula. Once again, it’s just Latin for cloud. It’s a rich star forming region.
Also, long, long ago, last century, in 1987, this area of the sky was home to the first supernova visible to the naked eye since 1604. We’re desperate to see a star blow up in our galaxy. Well, not too close. But we haven’t been able to see one since 1604. This is the closest we’ve have, 160,000 light years away, as we’ve saw it in 1987.
The other of the smaller galaxies is a little dwarf galaxy called the Small Magellanic Cloud. It has a mass of about seven billion times that of the Sun and as I mentioned, both of these are heading toward us. To some Indigenous communities, these two galaxies represent brothers who lived in the sky.
I’m going to start for the month of December, instead of talking about the Moon like I normally do (I will come back to it), I’m going to talk to you first of all about something that was discovered by the International Scientific Optical Network in Russia.
International Scientific Optical Network? ISON. Yes, we don’t know in advance how good this comet is going to be…. But late November and early December may be the comet not just of the year – because there’s been two already – earlier in the year we had Lemon and Pan-STARRS – but this may be the comet of the…. century.
Am I excited about Comet Ison? Absolutely! Is it guaranteed however to put on a show of a lifetime? Absolutely not! Yes, unfortunately, comets have a long history of breaking our hearts. They can promise a lot and deliver little or they can promise a lot and deliver it. We just don’t know. So what you need to do is keep checking our blog, Facebook and Twitter accounts for the most up-to-date information.
Sadly, it’s going to be at its best from the Northern Hemisphere. I am indeed heading towards the Northern Hemisphere just to see it. You cannot risk not looking in the sky late November / early December for this comet.
Which one is it again? It’s Comet ISON.
Getting back to our more mundane but no less spectacular highlights for the month of December 2014, we have the phases of the Moon.
New Moon will occur on Tuesday 3rd at 11.22am. First quarter Moon will be on Tuesday 10th at 2.12am. Don’t forget, this is about the best time of the lunar month to look at the Moon – whether it be with binoculars, a small telescope with a good eyepiece or even a telephoto zoom camera.
Full Moon will be on Tuesday 17th at 8.28pm. Last quarter, Thursday 26th December at 12.48am.
The summer solstice will occur at 4.11am on Sunday 22nd, and that means the Sun has reached its most southerly point from the celestial equator. And that’s at 23½ degrees away from it.
Don’t forget that the reason for the season is the axial tilt of the Earth. If the Earth wasn’t leaning to one side by 23½ degrees, we wouldn’t have these beautiful seasonal changes. But fortunately it does lean and we get to see the Sun appear to wander north and south of the equator in our yearly journey around the Sun.
Venus continues to set earlier throughout the month and will cease to be the evening star by the 11th of next month, so 11th January. So it is getting harder to see but it is still visible low in the west just after sunset.
On 5th December, the crescent Moon is just below Venus, and on the 6th it’s just above. So it’s a good marker to see just how much things change day by day.
At the start of the month, Jupiter is rising at around 10.30pm. So it’s only just a night object at the moment and not an early morning riser. But by the end of the month it’s rising by 8.30pm and spending the whole month in the constellation of Gemini.
It’s getting very bright because it’s approaching opposition on the 5th January – so still a little bit away. But it is going to be very bright throughout December.
From 9th to 12th, it will appear to go backwards in relation to the background stars in something that we call retrograde motion. So it’s well worth a look over these few days just to see that – hang on a second – it’s not moving quite how you would expect it to go normally. And this is something that has puzzled astronomers – not now, of course, as we know how the Solar System works – but for thousands of years, all sorts of bizarre models were introduced trying to explain this apparent backward or retrograde motion of the planets in relation to the background stars.
On 19th December, the Moon is also very close to Jupiter, the king of the gods.
Morning highlights for December. Well, pretty much, Mars, which is in the constellation of Virgo. On the 26th, the last quarter Moon will be nearby, just above and to the left.
It’s rising at around 2am (Mars, of course) at the start of the month, and closer to midnight by the end.
The planet Saturn will be in the constellation of Libra and close to the Moon on 2nd and 29th. This, by the way, is the best time to view Saturn for the entire year as the rings are tilted to us at 22 degrees. They’ll reach their maximum of 27 degrees in 2017 and then start to close up again until 2025 when they’ll be side-on.
Sadly, we won’t see that as it will be too close to the Sun at the time.
Also in the morning sky, the planet Jupiter around the 10th at 2am (boy, that’s an inconvenient time). If you have a small telescope but have a good eyepiece, please try to have a peek at Jupiter. If you do, and you’re very careful with the focus, you may just see the little volcanic moon, Io, drift in front of the planet and see its shadow transit the planet. It’s pretty hard to do but well worth a shot.
Another highlight for the early mornings of December are the Geminid Meteor Showers, which is one of the best for us in the Southern Hemisphere. You need to look north early in the morning on the 14th and 15th – but wait until the Moon has set.
These meteors, by the way, are caused by the Asteroid 32 Phaeton – what a spectacular name that is. According to Greek mythology, Phaeton was the son of the sun god, Helios. It’s about 5 kilometres in diameter and travels around the Sun every 524 days.
As it does this, for some bizarre reason as an asteroid, it does leave behind a little bit of dust. And as that dust collides with the atmosphere, at up to 35 kilometres per second, these things make the atmosphere heat up and glow, 40 kilometres and up. So, if you’re looking, short, sharp streaks of light on the mornings of the 14th and 15th, well worth the early morning rise.
If you’d like to know more about the happenings of the night sky, don’t forget to purchase your copy of the ‘Australasian sky guide’. And, being December, that means the 2014 version is out. It’s a spectacular little book written by Dr Nick Lomb from Sydney Observatory. You can purchase it at Sydney Observatory or the Powerhouse Museum shops or good bookstores for $16.95. And you can purchase it online at our website but an additional postage and handling charge applies.
For the most up-to-date information, don’t forget to check our blog at the Astronomy section of the Sydney Observatory website. That’s www.sydneyobservatory.com.au And you can follow us on Twitter @sydneyobs or look for sydneyobservatory (all one word) on Facebook.
This podcast is available monthly at www.sydneyobservatory.com.au/monthlyskyguides or you can subscribe through iTunes.
My name is Geoffrey Wyatt. I’m the Education Officer at Sydney Observatory, and I hope you’ve enjoyed your tour of the December 2013 night sky. And – happy new year!