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 audio sky guide is presented by Geoffrey Wyatt, senior astronomy educator at Sydney Observatory.
SEE THE SKY MAP
We provide an embedded sky map (below – it can take a moment or two to load) and this September 2011 night sky chart (PDF) which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view the PDF star chart, 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 2011 Australian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2010 until December 2011 inclusive (next year’s, covering December 2011 to December 2012 should be available from November), 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.
READ THE TRANSCRIPT (after the jump)
Hello. I’m Geoffrey Wyatt, Senior Astronomy Educator here at Sydney Observatory. We are talking to you about what is visible in the sky for the month of September. Don’t forget that September is the 7th month of the old Roman calendar but thanks to Julius Caesar and later the Gregorian reform, it is now the 9th month of the calendar.
You may need a few bits and pieces to help you with this tour of the sky. Of course, you’ll need a printed copy of our star chart which is available from www.sydneyobservatory.com.au [or downloadable from the link above if you’re reading this on our website]. Or of course, if you have your ‘Australian sky guide’ book, that’s always a bonus as well.
Now, you need to wait until it is nice and dark. You need to get yourself into a lovely position where you can see as much as the sky as possible. Obviously, if you are at the bottom of the hill or a valley that is going to restrict what you can see – so preferably up nice and high with a clear view of the cardinal directions that will allow you to see much more of the sky; make things easier to find.
We’re going to start off our tour for September by looking up quite high in the sky and then we are going to come back down towards the west. So, first of all, find your view towards the west where the Sun has just disappeared. You might have a slight reddish glow of twilight over there.
I want you to look up about 45 degrees above the horizon almost due west. This of course raises a slight problem. Forty-five degrees, well, that’s not too bad – halfway up of course, overhead being directly 90 degrees up, and horizontal – zero so, 45 degrees – halfway up.
There is a fairly easy way for us to navigate around the sky once we do have our cardinal directions of north, south, east and west and that is to use your fist held at arm’s length and your fingers spread from pinkie to thumb tip. And of course, even the pinkie held at arm’s length. Now, it varies from person to person but roughly speaking, your clenched fist held at arm’s length is about ten degrees. If you are a big chap like me, well, it’s a bit more, but I’ve learned to accommodate that.
So, if you hold your outstretched hand at arm’s length from pinkie to thumb tip is about 15 degrees for the average size person. So, we start it off looking due west after sunset, when it is dark. Stretch out your pinkie tip to thumb tip and then go three of those hand-spans, if you like, up and you should be able to see the 16th brightest star in the night sky. It has a slightly orange reddish tint to it and it is called Antares.
It is the brightest star in the constellation of Scorpius although some people call it Scorpius. Scorpius is a very interesting constellation and I’ll talk more about that in just a moment but we’re using Antares, if you like, as our starting point.
This is a fairly interesting star because it is so big and because of its colour. Quite often people don’t realise just how much colour is visible in the night sky. Most of the stars do appear whitish but there are a few bluish and there are a few orange-reddish stars and this is one of those. Antares means ‘rival to Mars’ because every now and then the planet Mars appears to pass quite close by and the two of them look fairly similar.
Antares is about 800 times the diameter if the Sun which means it is a very, very large star. In fact its colour and its size tells us it is a dying star. It’s like about 600 light years away from us which means we see it tonight in September as it was 600 years ago – rather intriguing.
Within the group of stars of Scorpius, Antares represents the heart of the Scorpion. It is one of the easiest pictures in the sky to see. So with a little bit of patience and a lot of imagination, supplemented, if you are old enough, by a glass or two of red wine and you might just be able to pick it up in the giant constellation of Scorpius.
A rather intriguing story goes with this group of stars. You see there was a mighty hunter called Orion and according to one of the more common myths in the sky, Orion boasted to the Goddess of the Hunt, Artemis, that he could kill any animal on earth.
Now, although Artemis was a hunter herself, she also offered protection to all creatures on the Earth. So, she created the giant scorpion to deal with Orion and the two went into battle. Apparently, it was a fierce and mighty battle, one of such interest that it even caught the attention of the King of the Gods, Zeus, himself. Eventually, Orion was killed by the Scorpion and Zeus placed the Scorpion into the sky.
Artemis also placed the body of Orion into the sky as a reminder for mortals to curb their excessive pride. But she placed the two of the constellations as far apart as they could possibly be. So it is very unusual to see the two in the sky at the same time. These stars however happen from time to time but not this time of year.
So, what you are going to look for from the heart of Scorpius, Antares, is head down towards the west ever so slightly and you come to a T intersection of stars. The middle star quite close by represents the head of the Scorpion and the claws go out towards either side, past back up through the heart and there is the star on the side. And then you follow the long hook-like line of stars that go around and form the tail with the sting.
Scorpius is a large constellation that’s relatively easy to see and there is a starting point for our tour in September. In fact we are going to go backwards at this stage and just drop down below Scorpius inside between Scorpius and horizon. We are going to look for the three bright stars of Libra, the scales, that make up, well, a triangle. They are fairly easy to see and they have fabulous Arabic names – Zuben Elgenubi, Zuben Eschemali, and Zuben Elakrab. Now my pronunciation may not be right but effectively they mean the head in the northern and southern claws of Scorpius.
You see these stars used to be part of the giant Scorpion but they’ve been broken off to make up the Scales of Justice that the Goddess Virgo carries. So, Libra, the Scales of Justice, is setting quite low in the west. Not so easy to see – but if you can make out a big triangle between Scorpius and the horizon, you’ve done well.
At this point, we’re going to go back up the sky, if you like, passing through Libra, passing through Scorpius, along an imaginary line known as the ecliptic. The ecliptic is the line along which the Sun, the Moon, and the planets follow through the background patterns of stars.
The background patterns of stars that we’re seeing at the moment, Libra, Scorpius, and the next one is Sagittarius, make up the path of the animals, the zodiac as we more commonly call them.
So at the moment, we’re almost looking directly overhead and we’re looking for the mighty half man, half horse archer of Sagittarius. Look, I have to tell you. It doesn’t matter how good your red wine imagination supplement is, if you’re trying to see a half man, half horse overhead, good luck. You’re far more likely to be able to see, well, a teapot.
So look overhead. Let your imagination go wild. Join the dots and if you can make out an old fashioned teapot, then you’ve found Sagittarius. Those of you born under the star sign of Sagittarius may not like being demoted from a mighty Centaur to a Teapot. Oh well: them’s the breaks.
Intriguingly, however, the Teapot is very close to the centre of our galaxy as we see it. So, looking directly overhead this time of year, we hit a beautiful view, still of Via Lactea. Via Lactea, by milk – the Milky Way. And it will branch off to the left and to the right, going north and south as we look at it, if you like, perpendicular to the line of stars that we’ve been following so far.
The Milky Way is, of course, the brightest part of our galaxy. And we could see perhaps two or three thousand stars and you get this magnificent bright band of glowing stars and gas and dust as long as you’re away from the city, as long as there’s no bright Moon anywhere in the sky to ruin the view, and as long as it’s a lovely, clear night.
So, if you’re away from the city, there’s no Moon, and it’s clear, looking overhead going from south to north, you should be able to see the Milky Way passing through the constellation of Sagittarius.
As you’re looking overhead, by the way, the centre of our galaxy is about 26,000 light years away and at the heart of our galaxy lies a super massive black hole, one of the most bizarre objects in the universe. The one at the centre of our galaxy, we call SagA* (pronounced as ‘Sagittarius A [ay] Star’). It has a mass many millions of times that of the Sun and it’s so big, it can gobble up a star relatively easily.
So that is directly overhead at the moment. Oh, and there’s no need to worry. At 26,000 light years away roughly, who cares what it gobbles up? It’s not going to be affecting us.
As we pass from high overhead through Sagittarius/Teapot, we go along the ecliptic down ever so slightly towards the east. We’re coming to the next of the zodiac star signs and that is of the half-goat, half fish, Capricornus.
Half goat, half fish? How do people come up with such bizarre creatures as this? You have to remember that many of these constellations have been around for thousands upon thousands of years. They’ve been made up to entertain and educate people as they sit around the camp fire after a long day working out in the fields.
So people would use the stars, I suppose you would say, as a palette and they would make up pictures to accommodate stories – stories of heroes and villains, great deeds, great journeys.
This particular pattern in the sky is used to represent a story of Zeus, Jupiter, King of the Gods, who was out on a picnic with a whole bunch of other Gods when the Earth cracked open and a demon from hell, Typhon, arose and began to attack the God Jupiter himself.
Most of the other smaller deities did the obvious thing and panicked and started to run away. In fact, the word ‘panic’, comes from this exact story. You see, the God, Pan, the goat that played the pan pipes, panicked and thought, well, he’s a demon from hell. There’s only one thing to do and that is change into a fish and swim to safety.
Halfway through the transformation, he realised that Jupiter, Zeus, needed a bit of help. He played a note upon his panpipes to distract Typhon, which allowed Zeus to gain the upper hand and Zeus banished Typhon back to hell. As reward for his assistance, Zeus placed Pan, as he was, half-goat, half fish, into the sky as the sea goat, Capricornus.
But what we’re going to be looking for is basically a triangular group of stars. And if you’re real pedant with your Euclidean geometry, you’re going to look for a triangle that has, well, a slightly bent hypotenuse. If you can see anything that looks like a bent triangle, or if you’re a ‘Star Trek’ buff, it’s a little bit like the ‘Star Trek’ logo, then you’re probably looking at the zodiac constellation of Capricorn, half goat, half fish.
The next of the zodiac, so long as we head down toward the east, is Aquarius, but Aquarius is a fairly difficult constellation to see. It represents the youth Ganymede, supposedly the most handsome youth on the planet that was snatched by the bird, Aquila, and carried to Mount Olympus to serve the gods water and wine.
The only bright stars that we can see in Aquarius are the shoulders of the youth, himself, and the line of water as it flows from his jug across the sky that meanders towards the mouth of the Southern Fish, Piscis Austrinus.
So Aquarius, I’m afraid, is a fairly difficult constellation to see, snuggled up to and wrapped around the constellation of Capricornus. Don’t worry too much because the next of these zodiacs rising in the east at the moment is Pisces, and Pisces is even fainter and more difficult to see. So these water zodiac signs, I’m afraid, are a bit too hard to see at this time of year.
But we’re now at the stage where we’re looking towards the east and we’re going to head around to our left as we look towards the north-east, and we’re going to look for a group of stars that looks like a giant square. You’ll find that astronomers, past and present, look for simple shapes and then give them rather curious and amazing stories.
So, we look at this giant square rising in the north-east. It’s not perhaps high enough for us to see fully yet, but you’re looking for the constellation, Pegasus, the Flying Horse. We do need to wait perhaps another month or so to get it to its best.
Continue towards your left and towards north, you’ll see a very large group of stars, if you have a clear view, that looks like a large cross. Much, much larger than the Southern Cross if you are familiar with it and once again, it will be quite low so you need a clear view.
What you’re looking at is Cygnus the Swan. And Cygnus the Swan is the home of the first suspected black hole, the first X ray source found in night sky called Cygnus X 1. And Cygnus is a very old constellation, one of the original 48 that were listed the by the second century astronomer, Claudius Ptolemy. And of course, it is one of the remaining 88 constellations that we have today.
If we continue past Cygnus, low in the north by north-east and around to almost due north, we’re going to look for the fifth brightest star in the night sky, Vega. It’s about 15 degrees above the northern horizon. Remember, 15 degrees for most people – a handspan from pinky to thumb tip, held at arm’s length.
Vega’s an intriguing star. It’s only 25 light years away. It’s relatively bright, as I said, being the fifth brightest star. And about 14,000 years ago, it was in fact, the North Polar star. If you’re all patient enough, it will be the North Polar star in another 11,000 years, although maybe that’s a tad too long for us to wait.
You see, everything changes position in the night sky. The stars may look fixed to us during our relatively short life spans, but the stars are all moving relative to each other. But of course, also, the Earth wobbles. It goes for a 26,000 year wobble and that’s why the star will become the North Polar star again many, many years in the future.
Vega is the brightest star in the constellation of Lyra the Harp. Lyra the Harp is intriguing because of many stories that relate to Vega and a nearby star on the other side of the Milky Way as see it, but not very far away at the moment. And that is Altair, Eye of the Eagle, which is about 47 degrees above the horizon at the moment.
So we go from 15 degrees from Vega up to three handspans, you’ll see another fairly bright star. Not as bright as Vega. This one’s the 12th brightest star in the night sky and it has an equidistant dimmer star on the other side. What you’re looking at there is the Eye of the Eagle, Aquila. And that’s the eagle that snatched Ganymede up into the night sky to become Aquarius, the Water Carrier.
The bright stars, Vega and Altair, represent a young boy or prince and a princess or a young girl in many Asian mythologies. To the Japanese, these two stars represent a princess and her prince in a festival known as Tanabata, celebrated on the 7th July each year. But very similar stories are told about these two stars in Korean and Chinese mythology as well.
So as you’re looking north at these two bright stars, this is an interesting point in time to think about it. I’ve mentioned so far, Greek constellations. I’ve mentioned some Arabic names when we talked about the stars of Libra the Scales, and now we have some Asian stories as well.
You see, just about every cultural group on this planet look up at the stars and use them for two different reasons. They use them to work out the time of year, therefore to keep track of the seasons and they use them to navigate, to work out directions.
What we’re going to do now is continue around towards our west back towards Libra, although Libra should be a little bit lower than where it was when we first started. Continue past the setting constellation of Libra in the west and we’re going to go around to the other centaur of the sky. Yes, there are two. Two half man half horses. One of them was really nice. One of them was a bit of a party animal.
We’re coming around to the nicer of the two and his name is Chiron and he is the constellation of Centaurus. Centaurus will be getting quite low in the south-west. Centaurus was a tutor, a teacher to heroes like Jason from Jason and the Argonauts, Hercules, and Achilles.
He’s also wrapped around the Southern Cross. The Southern Cross will be on its side at this time of year and only about 20 degrees up from the horizon. So, we’re pretty much at the end of the Southern Cross viewing season. It’ll be lost in the glow of the horizon, or more likely, trees and buildings.
As the Southern Cross disappears into the south-west, don’t forget that the Southern Cross doesn’t sit at the South Pole. We actually use it to point to the South Pole, but it really is a bit too low for us to do at the moment.
So what I want you to do is if you can see the mighty Centaur with its two bright Pointers, which represent the front feet of the horse. See if you can see, according to our map and it really is crucial that you have the star map there, the half man, half horse wrapped around the Southern Cross, setting in the south-west.
We’re going to continue through the deep south because there’s nothing terribly bright there at the moment and continue around, now, towards the south-east. I want you to look for the ninth brightest star in the night sky. It’s a rather intriguing star called Achernar. It’s also one of the flattest stars in the night sky.
Whenever you get a flat star, hopefully you know that stars are not just pinpoints of light. They are, in fact, typically spherical, although they do tend to flatten out around the top and the bottom because they’re spinning.
Well, this star, the brightest star in the constellation of Eridanus the River, called Achernar, is one of the fastest spinning stars we’ve ever seen. It bulges around the equator about 50 percent more than it does around the polar circumference because it spins roughly 15 times faster than the Sun. It’s about eight times the diameter of the Sun as well, and it’s relatively bright as I mentioned being the ninth brightest star in the constellation of Eridanus the River.
Interestingly, in classical earlier times, the name Achernar was given to a different star, a star that we now know as Theta Eridani or Acamar. Acamar, Achernar. They sound very similar. What happened was, Acamar used to be the brightest star at the end of the constellation of Eridanus the River as it was visible from Greece.
However, when people started to sail into the southern skies, they could see this nearby brighter star. They extended the river and changed Achernar to Acamar and gave the new brighter star the former name. Oh goodness me, confusing isn’t it? But according to its old Arabic name, Al Ahir al Nahr, it means the same thing, the end of the river.
As we continue past Achernar, we go towards the constellations which are extremely difficult to see of Phoenix and Sculptor as we continue back around towards the east to where we now see Pisces, a little bit higher in the sky, but no less difficult to see. We need to give Pisces a little bit longer to get up.
Planetary and lunar highlights for September 2011
First quarter Moon will occur on Monday 5th at 3.39am. Full Moon on Monday 12th at 7.27pm. Last quarter on Tuesday 20th at 11.39pm. And new Moon on Tuesday 27th at 9.09pm.
The spring equinox occurs at Friday 23rd at 7.05pm.
In the evening sky shortly after sunset, Venus will be very bright low in the western sky still in the constellation of Virgo.
And on 28th September, the thin crescent Moon will be immediately to the left of the planet. However this is only a day after the new Moon, so the Moon may in fact be a little bit too hard to see. Nonetheless it will be a spectacular sight as Venus is right next to – well, within 2 degrees, of the planet Saturn, and the Moon.
So mark in your calendar 28th September – make sure you get a clear view towards the west immediately after sunset.
On 1st September the crescent Moon will be above and to the left of the planet Saturn. In the morning sky on 23rd the crescent Moon will also be above and to the left of the fairly dim planet Mars, while on the next morning it will be slightly to the right of Mars.
On 17th September the gibbous Moon will be below and to the right of Jupiter.
Don’t forget, if you’d like to get more information about what’s visible in the night sky, you can purchase a copy of ‘The Australian sky guide’ by Dr Nick Lomb or visit our website for more details at www.sydneyobservatory.com.au.
My name is Geoffrey Wyatt, the Senior Astronomy Educator at Sydney Observatory, and I hope you’ve enjoyed your tour of the September night sky.