To help you learn about the southern night sky, Sydney Observatory provides an audio guide, transcript of that audio, and a sky map or chart each month. This month’s guide is presented by Geoffrey Wyatt, Sydney Observatory’s Education Program Producer.
Wrapped in a blanket and clutching a warm beverage, Geoffrey takes you on a tour of the southern sky at night, recounting stories of modern and ancient times from Gaia, Goddess of the Earth to ‘Forbidden Planet’ that describe the constellations above our heads.
See the Sky Chart
We provide an September 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
Hello there. I’m Geoffrey Wyatt, one of the team here at Sydney Observatory, part of the Museum of Applied Arts and Sciences. I’m going to talk to you about what’s visible in the sky for the month of September.
What we’re going to do is a tour the night sky so of course you’ll need some provisions. Somewhere warm and comfortable to sit, a blanket, a cup of coffee or Milo, or if you’re old enough perhaps a glass of red wine to assist your imagination. One of the most important things that you can have with you is your printable map, the September 2017 night sky chart (PDF).
If possible I want you to find a high position so that 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 just can’t help that. So make do with what you’ve got, but if you can, a clear view in all directions will make all the difference.
Wait for Sun to set and then a little more until it’s nice and dark perhaps up to an hour or so after sunset. Look up and what do you see? Clouds? Possibly. Stars? Hopefully. ‘For some, who are travelers, the stars are guides. For others they are no more than little lights in the sky.’ As said in The Little Prince by Antoine de Saint-Exupéry. I would like us all to be travelers together and we shall begin by looking toward the western horizon.
From there, go straight up to about 60 degrees or three outstretched hand spans from pinkie to thumb tip.
What you’ll see is 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 and 600 light years away. It is, Antares. It’s the brightest star in the group of stars, or constellation, that we call Scorpius.
A light year 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 about 9.5 x 10 to the power of 15 metres. For those of you that like kilometers, 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 ‘light year’. You’re seeing this star is as it was about 600 years ago. You are looking back in time.
Antares, its name came about because every now and then, roughly every 800 days or thereabouts, the planet Mars wanders fairly close by. The Greek name for Mars is 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.
When you look into the night sky, you might be able to see around 2-3000 objects depending on your age and eyesight. It’s very hard to remember which one is which unless you have a memory aid, something to help you. A dot-to-dot picture with a good story behind it is a fairly handy way of doing it.
To the ancients, the area of sky that we’re looking at now appeared like a small but nasty animal. Antares marks its heart. There’s a star on either side which should make up the body. If you go down just a little bit toward the Western horizon, there’s a perpendicular line of stars, which will be the head and claws on either side.
Claws, head in the middle, go up through a line of three stars with Antares in the middle then curling up around will be the long and dangerous tail of the scorpion. Scorpius is a constellation and a constellation is simply a region of the sky. Many of the figures in constellations are hard to identify until you see them on a map or someone points them out but once you’ve seen them they are easy…with a little practice. And constellations are a bit like a 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 and 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 and Scorpius is one of the more famous. It has many good stories about it but as you can imagine the stories that we have now may not be the same as they were thousands of years ago.
One that I particularly like revolves around another very famous constellation, the mighty hunter Orion. He boasted that he could kill any animal on the planet. This displeased Gaia, the Goddess of the Earth and protector of animals, so she created the giant scorpion ‘Scorpius’ to kill him.
So epic was the battle that even Zeus himself, king of the gods, stopped what he was doing and watched the fight. Ultimately Orion was killed by the scorpion and Zeus placed the scorpion in the sky for us all to see. But Artemis, goddess of the hunt who was a good friend took pity on Orion and placed his body in the sky as well but on directly the opposite side of the sky so that the two would never fight again. This very simple stick figure of a scorpion therefore 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 are some nice objects there including some lovely clusters of baby stars called M6, the Butterfly cluster and M7. They’re simply the sixth and seventh objects in the catalog developed by a man whose name began with M, Charles Messier. It was done quite some time ago but we still use it and these are rather pretty groups of young stars.
Once you’ve done that go a little bit higher but you will need to have our 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 a few seconds. [hums] 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 perhaps you’ve been shown because it 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 points to the centre of the Milky Way galaxy.
If you can get away from the bright city lights and there’s no Moon and you look up at this time of year you should be able to see a glorious view of Via Lactea, ‘By Milk’, our galaxy, the Milky Way. It is breathtaking.
Try and find the teapot because if you do find it and in particular the spout, in that direction roughly 26,000 light years in that direction is the heart of our galaxy and an object called Sagittarius A Star. (Written as Sagittarius A *)
It is a massive black hole roughly four million times the mass of the Sun. NASA’s Swift space telescope has been observing it and in 2014 it gave astronomers enough data to work out that it’s roughly 44 million kilometres in diameter. 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 and no size. Oh dear, that makes my head hurt.
Around that singularity there is a sphere, a sphere of influence called the event horizon and that event horizon is the part with a diameter of 44 million kilometres. Travel over the event horizon and…uh-oh, it’s not good times ahead. In fact, we call it ‘spaghettification’, being 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.
Let’s move along from Sagittarius and start to head down toward the East. 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 do is look for is a group that looks a bit like a triangle that’s been bent. Technically I suppose that makes it a quadrilateral and what you’re looking for is Capricornus, the half-goat half-fish.
As we leave Capricornus I want you to just go down a little bit more. This constellation is also very hard to see but once it’s been shown to you I think you’ll find 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, he was the most handsome youth ever and was carried from the Earth up to Mount Olympus by Aquila the eagle where he became the water carrier.
I take it back, it’s actually pretty hard to see but from Aquarius there is a line of stars that seems to meander across the sky to a bright star that you can see about 30 degrees, so that’s one hand span for 20 degrees and one clenched fist for about 10 degrees above the eastern horizon. It’s a relatively bright star called Fomalhaut, the mouth of the southern fish or Piscis Austrinus. Long long ago Fomalhaut used to mark the position of the winter solstice as seen from the northern hemisphere but no longer. That point has moved on because of the Earths precession of the equinoxes.
Fomalhaut is a fairly young star. It’s only about 400 million years old 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 toward the North.
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. As we go a little bit further toward the North past another group of stars that looks like a large faint cross. You’d need a perfectly clear view toward the North to see this one. It is the constellation of Cygnus the swan and the home of the first suspected black hole ever found and it’s 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’ve said before that’s roughly one outstretched hand, pinky tip to thumb tip, above the horizon. What you’re looking for is the star 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 12,000 years ago it was the North Polar Star. It seems that many people think that the stars never move but they do and the patterns change over very, very long periods of time. The Earth also wobbles over a 26,000 year period know as the precession of the equinoxes. So 12,000 years ago Vega 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 the fifth brightest star called Vega. By the way, again, for the science fiction buffs, it was the destination star in the fabulous 1956 movie ‘Forbidden Planet’.
If you go from Vega at roughly 18 degrees above the northern horizon up to about 35 degrees, so that’s one hand span with the fingers wide open, one clenched fist and then half a fist. Got that? Good.
If you can do that you will see another fairly bright star. This is Altair ‘eye of the eagle’. That was the eagle that carried Aquarius up to become the water bearer.
Vega and Altair, the two bright stars separated by the Milky Way, the river in the sky. Throughout Asia on the 7th of July legend says that birds come together and build a bridge over the Milky Way so the two can be together for just one day.
Oddly, nothing actually happens in the sky but I love this story and in Japan the girl, Vega is known Orihime, meaning the princess and the boy is Hikoboshi. In China it’s Zhi nu and Niulang. My pronunciation however may be off somewhat so please forgive me. This story is also quite famous in Vietnam and Korea. The sky really is a multicultural delight.
Continue now to turn to your left past where we started. To the southwest we’re looking for a second centaur half-man half-horse and this ones’ name 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 looking for is a fairly bright star that makes up one of his front feet. Its altitude is about 40 degrees above the horizon. How do we do that? Aha of course, two hand spans, pinky to thumb tip, that’s about 40 degrees. 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 about this star Alpha Centauri is that it’s a visual binary which means that if you have a small telescope this one star looks like two snuggled up against each other.
In reality 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 the planet Uranus. At their most distant nearly double that from the Sun to Neptune. One of them is a little bit bigger than the Sun, one of them a little bit smaller, but it’s a little more complicated than just being a binary star because there is a third star in the system. The third star is a small red dwarf going around the other two going around one another. The third star comes closer to us than other star apart from the Sun and is called Proxima Centauri at 4.24 light years. Recently in the search for exoplanets, a small planet just a little bigger than the Earth has been detected in orbit around Proxima Centauri. It takes about 11 days to go around once so it’s very close to the parent star but because it’s not as big or as hot as the Sun that actually puts this planet called ‘Proxima B’ into what’s called the ‘Goldilocks’ zone.
Theoretically it means that liquid water may exist on this planet. Stay tuned because I am sure over the next few years there will be more studies and information released about this intriguing new and close exoplanet.
Just below Alpha Centauri is the second brightest star in the Centaur so it is called Beta Centauri. It represents another 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 and that is the Southern Cross. It’s getting a bit low in the southwest at this stage and too hard to see.
Keep going around to your left, past due South and into the southeast. You’ll see the 9th (Corrected 21 Sep from 10th) brightest star in the night sky. That is Achernar 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 but 3,000 times brighter. It’s very, very bright, but because of the distance it fades to being about the 9th brightest as we see it.
It’s also intriguing because it spins so quickly its equatorial diameter is about 56 percent more than its polar diameter. That makes it one of the flattest stars we’ve ever seen.
When we look up and see stars we see mostly single points of light scattered here and there but that is not the reality. The majority of stars come in groups of two or more and they are as close to immortal as we can imagine. Our galaxy, and indeed the universe in which we live, is a very unusual and beautiful place.
Special events for September 2017 and let’s start with the Moon.
Full Moon is on Wednesday the 6th at 5:03pm,
Last quarter Moon is on Wednesday the 13th at 4:25 pm.
New Moon is on Wednesday the 20th at 3:30 pm.
First quarter Moon will be on Thursday the 28th at 12:53 pm
The spring equinox will occur on Saturday the 23rd at 6:02 am. 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 however it’s the autumnal equinox. On the equinox the Sun will rise due East and set due West.
At the start of the month sunset is about 5:37pm by the end of the month its drifted 20 about minutes out to 5:57pm. At the start of the day sunrise at the start of the month is 6:14am and by the end of the month at 5:34am, a difference of 40 minutes.
Jupiter starts the month low in the west in Virgo getting more and more difficult to see by the end of the month the best view for the year has passed. On 22 Sep the thin crescent Moon will to the north or below and to the right.
Saturn is high in Ophiuchus the 13th zodiac. On the 26th the crescent Moon is below but by the next night it will be above and to the right or north of yellowish Saturn.
In the morning sky Venus draws nearer to the rising Sun and will get harder to see by the end of the month. So the best chance to see it is early September about an hour before sunrise but you will need a very clear view to the east.
Even lower are both Mercury and Mars but they are too close to the Sun for us to see at the moment.
You can find our monthly sky guide podcasts on iTunes. If you want more detailed sky maps, sunrise and sunset times, Moon and tidal times, and a whole lot more, 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 shops and of course online at www.maas.museum. If you come in to our venues it’s only $16.95 but a little bit more if you order online with postage and handling.
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 at our account, @sydneyobs.
My name’s Geoffrey Wyatt, I’m one of the team here at Sydney Observatory and the Museum of Applied Arts and Sciences. I hope you enjoyed this tour of what’s visible in the southern sky for the month of September 2017.