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 Dr Andrew Jacob, one of the astronomy educators at Sydney Observatory.
SEE THE SKY CHART
We provide an embedded sky map (below – it can take a moment or two to load) and this October 2011 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 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 will be available from mid-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 (a packing/postage fee applies for online purchases).
READ THE TRANSCRIPT (after the jump)
Hello, and welcome to the night sky guide for October. My name is Andrew Jacob and I’m one of the evening guides here at Sydney Observatory.
To make the most of this podcast, you’ll need to gather a few things together. You’ll need one of the star maps, which you can collect from Sydney Observatory’s website at www.sydneyobservatory.com.au. Navigate your way through to the night sky podcasts and download one of the monthly sky maps. That map will show you what stars and constellations are in the night sky for October, and I’ll be referring to that map during this discussion.
As well as the star map, you should gather a few other things. A torch covered with red cellophane is very useful. The red cellophane will allow your eyes to remain dark adapted during the evening and you’ll also be able to read your map. A pair of binoculars can be very handy and I’ll give you a couple of objects later on that you’ll need the binoculars to see. If you don’t have the binoculars or a telescope, don’t worry, but they’re quite useful.
We also need to know a couple of directions: north, south, east, and west. You can find those locations from a street directory or just remember, of course, that the Sun rises in the east and sets in the west. And if the Sun is setting over your right shoulder, then you must be facing south. Another useful direction is the zenith. That’s the point directly overhead.
A couple of other measurements are useful as well. If you hold your hand out at arm’s length and stretch out your little finger and thumb, they span a distance across the sky of about 15 degrees. This is a useful way of measuring your way across the sky; so a hand span at arm’s length is 15 degrees. A fist held out at arm’s length makes an angle across the sky of about 10 degrees.
One thing you should be aware of for October in 2011 is that daylight saving begins at 2am on Sunday, 2nd October. Don’t forget to put your clocks forward by an hour on that night.
Let’s start our tour of the sky by looking towards the south. If you’re facing south and you look slightly to the right of south, almost to the south-west, you should be able to see two bright stars one above the other. If you’re in a bright light-polluted location like the city, they should be very clear. In the countryside, they should also be clear, but there will be a lot of other fainter stars around which may confuse things.
Nevertheless, these two bright stars, one above the other, are the two Pointers, the two famous Pointer stars which help us find the Southern Cross in the sky, perhaps the most famous constellation in the Southern Hemisphere. On your star map, they’re clearly labelled as the Pointers.
One of them is Alpha Centauri and the other one is called Beta Centauri. Both of the stars are in the constellation Centaurus. If you draw a line downwards, an imaginary line downwards from Alpha Centauri through Beta Centauri, and extend that line down towards the horizon, it should point you straight towards the Southern Cross. It’s tipped over on its right hand side, but otherwise, it looks just as it does on the Australian flag.
The important thing about the Southern Cross is it can help us find where true south is. If you measure out the long arm of the cross by holding two fingers up from the right hand star to the left hand star, and extend the arm of the Southern Cross towards the left by about four times, the point you end up at is the South Celestial Pole, the point in the sky about which all the stars are rotating. But there are no bright stars in this area. It’s an imaginary point in the sky.
Now, directly down to the horizon from the South Celestial Pole, if you draw a vertical line straight down to the horizon, you’ll find south on the ground.
If you were to take a photograph of the part of the sky including the South Celestial Pole and leave your camera shutter open for 10 minutes, 15 minutes, half an hour maybe, you’d find beautiful circular star trails across your photograph.
Now that we’ve found the distance from the Southern Cross, extended the arm of the Cross four times to find the South Celestial Pole, use your handspan at arm’s length and measure, in the same direction, another two handspans beyond that Celestial Pole position and you should come across a fairly bright star in the south-east of the sky.
This bright star is the star, Achernar. It’s a hot, blue white star about 144 light years away from us. It represents the end of the river, Eridanus, in the sky, the constellation Eridanus the River, and represents, perhaps, in ancient times the Nile.
If you’re in a dark location, well away from city lights, you might have noticed as you were measuring your handspans across the sky to Achernar, two faint, fuzzy cloud like objects. They’re located between the South Celestial Pole and the star Achernar. These two hazy clouds are called the Magellanic Clouds. They were first seen by Europeans hundreds of years ago and named after the explorer, Magellan.
One is slightly larger than the other. The Large Magellanic Cloud is about halfway down to the horizon from Achernar, and the Small Magellanic Cloud is just above that. These are two small galaxies that are orbiting our own Milky Way galaxy, and they’re gradually being torn apart as they’re absorbed by the Milky Way galaxy.
Let’s turn to the west. In the western sky, if you’re looking due west, hold out your arm and measure two handspans above the western horizon. You should reach a bright orange coloured star.
Some people have trouble seeing colours in the stars at nighttime. So if you don’t see the colour, don’t worry. Some of you may see it as a deep red colour. Some of you may see the star as an orange colour. It’s likely to be twinkling, as well.
This star is the star Antares, which means ‘the rival of Mars’ because of its red colour. It’s an enormous red, super giant star around 400 times the diameter of our Sun. If you placed it where our Sun is, it would stretch out through the Solar System and engulf the Earth. It’s a star on its last legs coming to the end of its life.
It’s about 604 light years away from the Earth so when it does eventually die, it will have no effect on the Earth, although it will be a spectacular sight. Unfortunately, that’s going to be long after any of our lifetimes.
I mentioned light years. Light years are simply a way of measuring distance in space. If you shine your torch up into the sky, for a moment, the light from your torch is travelling at the speed of light, about 300,000 kilometres every second. It reaches the Moon in about one second. If you let that light travel for 604 years, it’ll finally reach out to the distance of the star Antares.
Now, Antares is the heart of Scorpius, the Scorpion in the sky, one of the few constellations that really looks like its name. If you have your star map with you, hold your star map up towards the west. Identify the star Antares on your star map. Just below Antares, you’ll see the head and shoulders of the Scorpion.
Now, come back through Antares and stretching up into the sky above Antares almost overhead, is a back to front question mark. That’s the tail of the Scorpion. At the very end of his tail, you can see his sting quite clearly. It really does look like a scorpion.
Let’s move on. To the right and above Scorpio’s sting is the constellation Sagittarius, which is supposed to represent an archer, but I’ve never been able to see an archer when I look at this set of stars. All I can see is a good old fashioned Teapot.
If you’re using your map that you’ve downloaded from the Sydney Observatory website, you’ll see it identified on that map. Look closely and you should be able to identify an upside down teapot, tipping tea over Scorpio’s tail.
Just off the tip of the teapot is an interesting point in the sky. If you’re in the countryside, you will have noticed the Milky Way stretching far overhead, that band of faint light stretching from the Southern Cross over on your left, past the two Pointers, stretching over through Scorpio’s tail, and off to the northern horizon on your right hand side. The centre of our Milky Way galaxy lies just below the tip of the Teapot, not far also from Scorpio’s sting.
It’s a good thing we’re a long way from the centre of the Milky Way galaxy. At the centre of our galaxy lies a very large, black hole about several million times the mass of our Sun. We’re quite safe from it out here on the edge of the galaxy where we lie.
Let’s turn to the right again and look to the north. There are a few bright stars in the north and some fairly faint constellations. Let’s start by looking directly north. Just 10 degrees, or one fist width at arm’s length, above the northern horizon, you should see a star, probably twinkling wildly because it’s so close to the horizon. This is the star, Deneb, in the constellation Cygnus. We’ll come back to the constellation Cygnus in a moment.
Just under two handspans to the left is another reasonably bright star, again about a fist width above the horizon. This second star is Vega in the constellation Lyra.
Now, these two stars form the base of a triangle. Above them, about three handspans above the horizon, you’ll find the star Altair, which to some of you may look subtly yellowish.
These three stars don’t look particularly special to us in the Southern Hemisphere. In the Northern Hemisphere, however, they’re known as the Summer Triangle. They’re very high overhead and very distinctive from the Northern Hemisphere. So if you ever travel over there, have a look for the Summer Triangle made of the stars, Deneb, Vega, and Altair.
Let’s go back to Deneb for a moment. Deneb is a blue white, supergiant star over a 100 times the diameter of our Sun. So although it’s not as big as Antares, the supergiant in Scorpio, it turns out that it’s an extremely bright star. It’s 3,200 light years away from us. At that extreme distance, it still looks, in our nighttime sky, to be a bright star. If we were to place it where the Sun was, we would be blinded by its light and frazzled by the ultraviolet light that it puts out.
Deneb is in the constellation Cygnus, the Swan. If you have your star map with you, turn your star map around so that north is at the bottom and then you’ll be able to align your star map with the stars you see in front of you, which are also to the north.
Match up the stars near Deneb to identify the Swan. Its wings stretch down to the left and up to the right and its long neck stretches out and up to the left.
Altair, just above Cygnus, is in the constellation Aquila the Eagle. The Eagle also has its wings stretching out to the right and left and its head pointing up and to the left. If you’re in a dark site, well away from city lights, you’ll be able to see the Milky Way in this region and you’ll be able to see these two birds flying along the Milky Way, heading south.
So now we’ve looked at constellations and stars to the south, to the west, and to the north. We could turn to the east, but in October, there aren’t that many bright stars nor any truly distinctive constellations over there. So let’s leave that direction until next month.
What are the special events and highlights for October 2011? Let’s start with the phases of the Moon. The times I’m about to give you are in daylight saving time. Daylight saving begins at 2am on Sunday 2nd October. Don’t forget to put your clocks forward by an hour that night.
First quarter Moon will be on Tuesday 4th October at 2.15pm. The full Moon will be on Wednesday 12 October at 1.06pm. Last quarter will be on Thursday 20th October at 2.30pm. And new Moon will be on Thursday 27th October at 6.56am.
What planets are visible in October 2011? Let’s start with the evening planets. Looking towards the west, we’ll see Venus following the Sun down, setting shortly after sunset. You can recognise Venus because it is extremely bright, and a very white light, shining like a spotlight from the western sky.
From the middle of the month, it’s joined by Mercury, a much fainter object – but you should see Mercury just below Venus towards the end of the month.
If we turn to the east, we’ll find Jupiter, our largest planet, rising about an hour after sunset. And through most of the night, you’ll see it high up in the sky and travelling across to the western sky by early morning.
If we move to the morning sky, we find Mars, a distinctly red-coloured planet, in the north-eastern sky. In the morning, again, turning towards the north-west, you’ll see Jupiter setting late in the morning.
A couple of interesting events are happening in October with the planets. Jupiter is at what we call ‘opposition’ on 29th October. That means that it’s in almost direct line with the Sun and the Earth and out to Jupiter. At that time it’s at its brightest, and its closest to us and through a pair of binoculars it will look quite spectacular. A little larger than normal – but certainly not visible as a disk to your naked eye.
If you have those binoculars, have a look at Jupiter. Look for its cloud bands. See if you can find the red spot. And look for the moons of Jupiter – the four bright moons you see dancing around Jupiter.
On 28th October, a nice grouping of planets and the Moon occurs at about 8pm on 28th October, look towards the western sky, you’ll see a thin crescent Moon, and just below it, Venus, looking bright and white. Just to the left of Venus and also below the Moon you’ll see Mercury, the closest planet to the Sun.
So those are the Moon phases and the main planet events that are happening in October.
Don’t forget you can subscribe to our Sydney Observatory monthly sky guide podcasts on iTunes.
This has been Andrew Jacob from Sydney Observatory with the podcast for October 2011.