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 Senior Astronomy Educator.
Geoff fascinates us with his guide to the stars and constellations to look out for in September and also with insight into how astronomy was important to the ancient people of Mesopotamia, Greece and Rome.
Geoff tells us where and when to look out at night for the planets Mercury, Mars, Saturn in September. And he points out his highlight for the month, on 1st September when, shortly after sunset, Saturn, the Moon and Mars will all be in the constellation of Libra, with the Moon and Saturn just five degrees (or five pinkie widths) apart.
Listen to the September 2014 night sky guide audio, or read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a September 2014 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.
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 2015 inclusive (or wait till November when you can purchase the 2015 book), 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 September 2014 monthly sky guide audio
Hello there. I’m Geoffrey Wyatt, education officer here at Sydney Observatory. I’m going to talk to you about what’s visible in the seventh month of the old Roman calendar before the reform of Julius Caesar in 46 BC, and that is, of course, the month of September.
Hold on a second. September? Seventh month? Yes, that’s right. Things got shuffled quite a long time ago, and now September is the ninth month. We all knew that anyway, but I think some of us have probably wondered why ‘sept’, meaning ‘seven’, is for the ninth month of September. Now you know.
Anyway, what we’re going to do is tour the night sky. Of course, you’ll need some provisions. The most important one is the printable map that you can download from our website. What we’re going to do is wait until about an hour or so after sunset until it’s nice and dark.
I want you to find a high position so you can see as much of the horizon as you possibly can in all four cardinal directions. That’s right: north, east, south, and west. If you’re up against your neighbour’s tree or house, then of course you’re going to lose some of the view, but some of us can’t help that. Just make do with what you’ve got, but if you can, a clear view in all directions will make all the difference.
We’ve waited for sunset. It’s about an hour later. It’s got nice and dark. What I want you do to, is to look towards the western horizon. From there, go straight up to about 60 degrees. Yes, I’m sure you’ve heard me talk about this before. 60 degrees – how can you measure that? Most of us can estimate 90 degrees, straight up, or half way, 45 degrees, but 60?
You have, built in, a handy (interesting pun) way of measuring what you can see in the sky. Hold your hand at arm’s length. If you clench your fist, that will measure about 10 degrees. If you hold out your pinky, that will be about one degree, or twice the size of the full Moon. If you spread your fingers, from pinky tip to thumb tip is about 20 degrees.
Our first point, due west, where the Sun has gone down, is about 60 degrees up, so that’s three handspans.
What you should be able to see is the first of – we don’t so much call it these days – four royal stars. It is a bright star that used to measure one of the four important points in the sky – the solstice and the equinoxes. This was done thousands of years ago from Mesopotamia, a wonderful cradle of civilization between the Euphrates and the Tigris rivers.
What we’re looking at is a star that’s 60 degrees up from the western horizon. It’s the 15th brightest star in the night sky. It’s a red supergiant, which means, of course, it’s a pretty big star. It’s about 15 times the mass of the Sun, 800 times the diameter of the Sun, 600 light years away. Aha, I think we’ve narrowed it down. It is Antares. Some people call it ‘AnTAReez’. It is the brightest star in the group of stars, or constellation, that we call Scorpius.
A light year, by the way, is the distance that light travels in a year in the vacuum of space. It’s a long way. For those of you who like mathematics, it’s 10 to the power of 16 metres. For those of you that like kilometres, it’s roughly 9,500 billion kilometres. It’s not a convenient way of thinking about it, to be honest, so we tend to use just a light year. What you’re seeing when you look at this star is as it was 600 years ago.
This is pretty high. We’ve actually gone up past another very famous group of stars called Libra. I’m sure you’ve heard of that. But look, it’s not perfectly positioned at this time of year, so we’ve gone past Libra straight up into the constellation of Scorpius. Not Scorpio – that’s the astrological name. Its astronomical name that, hopefully, we will all use, is Scorpius.
The brightest star in Scorpius is Antares. That name comes about because every now and then, roughly every 800 days or thereabouts, the planet Mars wanders fairly close by. The Greek name for Mars was Ares. As Ares, god of war, would go past this fairly bright, reddish star, they looked similar. This star was called the rival of Mars, anti-Ares, Antares.
As I’ve mentioned, this star was one of what we called four royal stars – a marker in the sky. There are certain crossover points, I suppose you could call them, the equinox and the solstice. Thousands of years ago, Antares marked the position of the autumnal equinox for the Northern Hemisphere, but I’ve got to remind everybody, that’s not the case now.
You don’t notice it, but the Earth does a rather spectacular and slow 26,000-year wobble on its axis called the precession of the equinoxes. Antares used to mark a position in the sky, the autumnal equinox, but no longer. It will again, however, I should say, in perhaps another 20,000 years, but who cares? We’re not going to be around for that.
Antares marks the heart of a small but nasty animal. When you look into the night sky, there are thousands of objects up there. Most of them are stars, of course. It’s very hard to remember which one is which unless you have a memory aid, something to help you. With two to three thousand stars up there, depending on your age and your eyesight, that you can see, a dot-to-dot picture is a fairly handy way of doing it.
To the ancients, the area of stars we’re looking at now appeared like a small but nasty animal. Antares, the heart. There’s a star on either side which at this time of year should make up the body. If you go down just a little bit towards the west, there’s a perpendicular line of stars, which will be the head, and on either side of the head, the claws.
Claws, head in the middle. Go up through a line of three stars with Antares in the middle the heart, and then curling up around will be the long, deadly tail of the scorpion. Scorpius is a constellation. A constellation is simply a region of the sky. Think of it as being the suburb. There are many suburbs in a city. As soon as someone mentions a particular one it gives you a rough idea of where it is. It’s the same with the sky.
Over thousands of years the sky has been mapped and broken up into, now, 88 different sky suburbs or constellations. This is one of the more famous ones, Scorpius. It has a good story going to it too. But as you can imagine being thousands upon thousands of years old, the story that we have now may not be the same as it was thousands of years ago.
One that I particularly like revolves around another very famous constellation, Orion the hunter. He was a mighty hunter that used to hang out with the goddess of the hunt, Artemis. He was half-god half-mortal. He made the rather silly claim that he could kill any animal on the planet.
This displeased Gaia and Artemis. So they created the giant scorpion Scorpius to go after him. So epic was the battle that even Zeus himself, the king of the gods, stopped what he was doing and watched the battle. Ultimately Orion was killed. Zeus placed the scorpion in the sky for us all to see.
But Artemis took pity on Orion and placed his body in the sky as well but on directly the opposite side of the sky as Scorpius so the two could never fight again. This very simple stick figure of a scorpion has a wonderful story behind it.
When you’ve been able to see the full constellation of Scorpius, if you have a pair of binoculars or a small telescope, scan around the tail region. There’s some nice objects there including some lovely clusters of baby stars called M6 and M7. There’re simply the sixth and seventh objects in the catalog developed by a man whose name began with M. It was done quite some time ago but we still use it. They are rather pretty groups of young stars.
Once you’ve done that go a little bit higher but you will need to have the printable map because the next group of stars is rather hard to see. What you are looking for is a half-man half-horse with a bow and arrow. Can you see it? I’ll give you five seconds.
Found it yet? I don’t think so. It’s nearly impossible. If you can see a half-man half-horse with a bow and arrow you’re doing very well or you’ve been shown. Because looking higher ahead right now you should be able to see what looks much more like an old-fashioned teapot.
Yes, that’s right. Those of you out there with the birthday star sign of Sagittarius – you’re now a teapot, unofficially of course. This group of stars is fairly important to look at because it marks the centre of the Milky Way galaxy.
If you’re away from the bright city lights right now looking up and there’s no Moon, you should have a glorious view of Via Lactea, “By Milk”, our galaxy, the Milky Way. It is breathtaking. It’s beautiful.
If you can get away from the city this is the wonderful time to look up and enjoy the Milky Way galaxy. Try and find that teapot. Because if you find that teapot and look at the spout of the teapot, looking in that direction roughly 26,000 light years away there is something rather special there. Lurking at the heart of our galaxy is an object called Sagittarius A*.
This is a massive black hole roughly four million times the mass of the Sun. It’s pretty big. NASA’s Swift space telescope has recently been observing it and been able to work out that it’s roughly 44 million kilometres in diameter.
That’s not a single object. Black holes are rather bizarre objects. At the centre of the black hole there is something called a singularity, a point, a mathematical point with infinite density. Oh dear, that makes my head hurt. But around that there is a sphere, a sphere of influence called the event horizon. That event horizon has the diameter of 44 million kilometres.
Go over that event horizon, uh-oh, it’s not good times ahead. In fact, we call it “spaghettification”, ripped apart atom-by-atom. But we don’t know for sure what happens once you go over that because you leave the observable Universe.
Clearly there’s nothing to worry about. Clearly nobody can go there. It’s simply too far away. But we think about these things and we think about the mathematics and the physics behind them. What we have done is with that Swift telescope observed that there is a very large gas cloud called G2. Yeah, not a very exciting name.
It’s about three times the mass of the Earth. This cloud is orbiting very, very close to this relatively quiet black hole. Mid this year…by the time you’ve heard this podcast it would have already happened…we think this gas cloud may get very, very close and in fact may interact with the black hole.
If it does the black hole will flare up in the X-ray part of the spectrum. We’re really looking forward to this and we should have some results shortly thereafter. At the centre of the galaxy is a black hole, Sagittarius A*, but do not go there.
Back to the story of Sagittarius, half-man half-horse with a bow and arrow. It’s pretty hard to see. It’s a lovely story. Again, as we said with lots of these constellations there are always ancient stories that go along with them of mythical creatures, battles and so on.
This particular centaur I must say is a fairly hot-tempered lad. There’s another centaur I’ll talk to you about fairly shortly who is much nicer. Let’s move along from Sagittarius and head down. You might have to actually turn around a little bit so you’re now facing the east. The next constellation down is the first of the water signs.
It’s a fairly faint group of stars. What I want you to look for is a group that looks a bit like a triangle that’s being bent. Technically now I suppose it’s a quadrilateral. If there’s any science fiction nerds out there you might like to try and see something that looks a bit like the Star Trek logo.
What you’re looking at is Capricornus. Capricornus is half-goat half-fish. When was the last time you bumped into an animal that was half-goat half-fish? No. Not likely, is it? Again, it relates to having an interesting story to use to memorise the positions of the stars and use them. People have been doing this for thousands of years, dot-to-dot pictures. It’s a very useful way of doing it.
I should point out of course that not all cultures do dot-to-dot pictures. The Indigenous peoples of Australia have often used just a single point, a single star, to tell a story. I’ll tell you one of those quite shortly. At the moment we’re still looking at Capricornus, half-goat half-fish.
The story goes that the gods were having a picnic when suddenly the Earth cracked open and the demon Typhon came out. Typhon attacked Zeus, king of the gods.
The goat Pan did the only obvious thing that he could do at seeing such a fight, he panicked, which is where we get the word from, and thought, “I’m out of here”. He started to change from his goat form into a fish to swim to safety. He got halfway through the transformation and thought, “Zeus is the boss. I’d better go back and help.”
He played a shrill note on his pan pipes which distracted Typhon long enough for Zeus to gain the upper hand and get rid of him with a thunderbolt. As a reward for his assistance Zeus placed Pan as he was in the sky as a half-goat half-fish. Amazing imagination. I just love it. Imagination and mathematics: the two of those combined will take us anywhere.
An interesting thing to note about this particular constellation as well is that it was in this part of the sky on September 23rd in 1846 that the planet Neptune was discovered by the German astronomer Johann Galle.
The planets, the “wanderers” as we used to call them, stick to a line across the sky called the ecliptic. You’ll never find the planets, the Sun or the Moon down near the Southern Cross or in the Big Bear, Ursa Major in the northern sky. They will always stick very close to this ecliptic. No wonder the planet Neptune was found in this part of the sky.
As we leave Capricornus I want you to just go down a little bit more. This constellation is also very hard to see. Once it’s been shown to you I think it’s not that hard. All you’re looking for are the shoulders, the jug and the line of water flowing from the zodiac constellation of Aquarius.
Aquarius was the water carrier. He represents the most handsome youth ever on the Earth that was taken from the Earth up to Mount Olympus by Aquila, the eagle, where he became the water bearer, Aquarius, that we now call him.
It’s pretty hard to see. But from this group of stars is a line of stars that seems to meander across the sky to a star that you can see now it’s about 30 degrees above the eastern horizon. It’s a relatively bright star. Guess what? It’s another one of our royal stars. It is Fomalhaut, the mouth of the southern fish.
Thousands of years ago, as I’ve already mentioned, this star marked the position of the winter solstice, the most northerly point of the Sun. That was in the past, no longer now.
Fomalhaut, the brightest star in the constellation of Piscis Austrinus, the southern fish, a long time ago used to mark the position of the winter solstice, the Sun’s most northerly movement as seen from the Northern Hemisphere. But again, thousands of ago, and it’s not the case any longer. Fomalhaut is a fairly young star. It’s only about 400 million years old, thereabouts, little bit give or take, and about 25 light years away. At twice the size of the Sun it’s pretty big.
After you’ve been able to see Fomalhaut…. By the way, the rest of the constellation to me looks a little bit like a paisley swirl with the brightest star at the bottom of it as we’re looking at it right now. What I want you to do is turn to your left, that means we’re going towards the north. We go around, we go around.
It’s pretty hard to see but we’re going to go past the constellation of Pegasus, which will look a bit like a big square, though it’s very low at this point in time. We go a little bit further towards the north. We go past another group of stars that looks like a very large faint cross. But you’d need a perfectly clear view towards the north to see that. That is the constellation of Cygnus the swan, the home of the first suspected black hole called Cygnus X1.
Go a little bit past that and what you’re looking for is the fifth brightest star in the night sky. It’s only about 18 to 20 degrees above the horizon. Remember as we said before that’s roughly one outstretched hand, pinky to thumb tip, above the northern horizon. You’re looking for the fifth brightest star in the night sky – Vega.
Again, like Fomalhaut, it’s only about 25 light years away and about twice the mass of the Sun. It’s less than 500 million years old so it’s a young star. But the cool part is about 12,000 years ago it was indeed the North Polar Star.
People seem to think that the stars never move. The stars are indeed moving. They move and the patterns will change over very, very long periods of time. The Earth also wobbles as I’ve mentioned. 12,000 years ago it was the Polar Star and roughly in another 14,000 years it will be the Polar Star again. But don’t worry about waiting for that one.
I love looking at this star, this fifth brightest star called Vega. Not only is it incredibly bright…. By the way, again, for the science fiction buffs, it was the destination star in the fabulous 1956 movie ‘Forbidden Planet’.
Apart from that I mentioned a moment or two ago that Indigenous cultures often used just a single star rather than a dot-to-dot picture. To the Boorong people of the Wergaia language group from north-western Victoria this actually represented Neilloan, the mallee fowl. When they’d see this star, Vega, as we call it today, setting in the north-west with the Sun that was the time to go looking for mallee fowl eggs.
There you have another fabulous use of the stars. Just about every culture around the world uses the stars to work out the time of year, so a form of calendrical marker, and a way of navigating. Pretty cool I think.
If you go from Vega at roughly 18 degrees above the northern horizon up to about 35 degrees. That’s one handspan with the fingers wide open, one clenched fist and then half a fist. Got that? Good. I want you to go about 40 degrees east of north.
Look north. That’s two hand spans with the fingers outstretched to your right, then up, as I said, 35 degrees. There’s another fairly bright star there. This is Altair, ‘eye of the eagle’. That was the eagle that carried Aquarius, whilst he was Ganymede, up to become the water bearer.
Vega and Altair, two bright stars. They’re separated by the Milky Way, the river in the sky. Throughout Asia, but strangely I don’t know why, on the 7th of July…Yes, this has already happened…. The legend goes that on the 7th of July the stars Vega and Altair, that represent a young boy and his princess, they’re separated, they’re lonely, they’re on opposite sides of the river. But birds come together, build a bridge and the two can be together for just one day.
Nothing actually happens in the sky. The legend is the two come together on the 7th of July for just one day each year. I love that story. In Japan the girl, Vega, is Orihime, meaning the princess and the boy is Hikoboshi. In China it’s Zhi nu and Niulang. My pronunciation may be off there.
These stories are also quite famous in Vietnam and Korea. Again, we’ve got this incredible multicultural use of the stars for thousands and thousands of years.
Now that you’ve had a look at Vega and Altair high in the eagle I want you to continue around towards the west, pretty much where we first started. We go past Libra, which is already pretty low down I’d say by this stage. We’re heading around towards a fairly famous group of stars. That’s the second centaur that I mentioned earlier.
This centaur, half-man half-horse, he’s the nicer of the two. Pretty hard to see unfortunately at this time but you can see the two brightest stars of his feet. The centaur is of course Centaurus, obviously. The stars in his feet, the brightest stars, are Alpha Centauri and Beta Centauri.
The centaur’s name, by the way, is Chiron. He was a wonderful teacher. According to mythology from long, long ago he was the tutor to Achilles, Hercules and Jason.
What we’re going to look for is a fairly bright star. Its altitude is about 45 degrees above the horizon. How do we do that? Two handspans, pinky to thumb. That’s 40 degrees, then half a clenched fist up. If you can see one bright star there you’ve nailed it. That’s Alpha Centauri. It’s the closest star to us after the Sun and the third brightest star in the night sky.
The interesting thing is it’s a binary. That means if you had a small telescope or even a really good pair of binoculars the two stars look like they’re snuggled up against one another. But they’re not. The distance between them varies enormously. They’re in a dance. A dance that takes roughly 80 years for them to go around each other once. At their closest they’re roughly the distance from the Sun to Saturn. At their most distant nearly double that to the distance from the Sun to Neptune. One of them is a little bit bigger than the Sun, one of them a little bit smaller.
Just below Alpha Centauri is Beta Centauri. It represents another one of the front feet of the half-man half-horse. From there there’s a line of stars that, again, you’ll need the star map to see, that wraps around indeed the smallest of all 88 constellations. That is the Southern Cross. It’s getting a bit low in the south-west at this stage. We’ll probably leave that for a few more months.
Keep going around towards the west, past the south into the south-east and you’ll see the 10th brightest star in the night sky. That is Achernar. Achernar is the brightest star in the constellation of Eridanus, the River.
It’s an amazing constellation because it winds its way across so much of the night sky. It’s an interesting star too at about 140 light years away; it’s seven times the mass of the Sun and 3,000 times brighter. It’s very, very bright, but because of the distance it fades to be about the 10th brightest.
It’s also intriguing because it spins so quickly its equatorial diameter is about 56 percent wider than its polar. That makes it one of the flattest stars we’ve ever seen. Curiously, this star with many of the others that I’ve mentioned come in groups of two or more.
Our view of looking up and seeing single points of light scattered here and there is not really what the big picture is about. Our galaxy, and indeed the universe, is a very unusual place.
Special events for September 2014. Firstly, let’s start with the Moon. First quarter on Tuesday the 2nd at 9:11 PM. Full Moon on Tuesday the 9th at 11:38 AM. Last quarter Moon will be on Tuesday the 16th at 12:05 PM, and new Moon on Wednesday the 24th at 4:14 PM.
The spring equinox will occur on Tuesday the 23rd at 12:29 PM. This is simply when we see the Sun move from the Northern Hemisphere and cross the celestial equator into the Southern Hemisphere, which for us signals the start of spring. In the Northern Hemisphere, it’s the autumn equinox.
A bit confusing as you go from one hemisphere to the other, but for us in the south, good times are coming as the Sun comes back.
Shortly after sunset, there are three planets visible looking towards the west, Mercury, Mars, and Saturn. First of all, Mercury. Quite low in the constellation of Virgo. On the 20th and the 21st of this month, Mercury is just one degree away from the brightest star in Virgo, called Spica.
In fact, Mercury will be one order of magnitude brighter than the star. It should be quite easy to see but you probably need to get out shortly after sunset and look for Mercury. It disappears quite quickly. After all, it’s named for the fleet-footed messenger to the gods. It never strays all that far from the Sun, as we see it.
On the 20th and the 21st, probably the best time of the month to see it. If you miss that, however, on the 26th of September, the thin crescent Moon will be just four degrees below the planet Mercury.
Mars, Ares, the god of war, will be on the move, passing through three separate constellations of Libra, Scorpius, and Ophiuchus.
On the 28th, towards the end of the month, Mars will be just three degrees, that’s three pinkies held at arm’s length, away from the star Antares in the constellation of Scorpius. As I mentioned earlier, that’s how that star got its name, because the two look so similar, Mars and its rival.
Going back to the first of the month, however, the crescent Moon is just five degrees to the right of Mars and the Moon will swing by again on the 29th and the 30th, but it won’t be as close. The planet Saturn is in the constellation of Libra. On the 28th of September, a very young crescent Moon will be less than two degrees away. It will be a lovely view.
In my opinion, the highlight through the evenings in September will be on the 1st. That’s when Saturn, the Moon and Mars will all be in the constellation of Libra, the Scales. The Moon and Saturn are just five degrees apart, with Saturn about seven degrees below the crescent Moon.
They won’t be easy to spot shortly after sunset, but it’s well worth a look. What I want you to do is make sure you visit our Facebook page just before, and we’ll have a very accurate map showing you where to look for each of those objects.
If we’re going to look at objects in the early morning, you’ve got to get up quickly, because for the early morning it’s farewell to the planet Venus as the morning star by the end of the second week.
Very low in the constellation of Leo, on the 6th you’ll be able to see Venus just 0.7 degrees from the brightest star in Leo, called Regulus, the Little King. It’s well worth a look. After that, we’ll lose it and we won’t see it again until we see it as the evening star in December.
The planet Jupiter is also very low in the north-east, in the constellation of Cancer, the Crab. On the 20th, the waning crescent Moon will be above and to the left by about seven degrees, less than a clenched fist held at arm’s length. The next day, on the 21st, it will be toward the right.
You can find our monthly sky guide podcasts on iTunes. If you want more detailed sky maps, sunrise and sunset times, the Moon and tide times, and a whole lot more information, we recommend that you buy the book ‘The Australasian Sky Guide’, by Dr Nick Lomb.
It’s available from Sydney Observatory and the Powerhouse Museum websites and shops. It’s only $16.95 if you come to our venues, but a little bit more with postage and handling if you order online.
Our website at www.sydneyobservatory.com.au has a galaxy of information about astronomy and visiting us at the observatory, how to use telescopes, see a program in our 3D Space Theatre, and visit the new Sydney Planetarium.
For the very most up-to-date information, why not engage with us via Facebook? Go to facebook.com/sydneyobservatory, or you can follow us on our Twitter account, @sydneyobs.
My name’s Geoffrey Wyatt, the Education Officer here at Sydney Observatory. I hope you enjoyed this tour of what’s visible in the southern sky for the month of September 2014.