Orionids meteor shower expected to peak on 21 October
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 Dr Andrew Jacob (pictured, right), Assistant Curator of Astronomy at Sydney Observatory.
This month, find out how to find the South Celestial Pole, and where to find stars and constellations including Crux (the Southern Cross) and the Pointer stars, the Large and Small Magellanic Clouds, the bright star Antares at the heart of Scorpius. Andrew also tells us when and where to see an alignment of the planets Mercury, Saturn and Venus during October. And of course, there is the Orionids meteor shower to look out for during the nights and pre-dawn during October.
For all this and more, listen to the October 2013 night sky guide audio, or read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a October 2013 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.
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BUY THE BOOK
Our annual book, ‘The 2013 Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2012 until December 2013 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). At this stage, you may prefer to wait until the 2014 book is available – expected to be in November.
READ THE TRANSCRIPT (after the jump)
Transcript of the October 2013 monthly sky guide audio
Hello, and welcome to the night sky for October. My name is Andrew Jacob, and I’m the Assistant Curator of Astronomy at Sydney Observatory. To make the most of this podcast, you should begin by gathering a few items together. Firstly, you will need a star map. You can download one from Sydney Observatory’s website at www.sydneyobservatory.com, where Sydney Observatory is one word.
Navigate your way to the night sky podcasts and download the star map for the month of October. The star map will show you what stars and constellations are visible in the night sky and I will be referring to that star map during this discussion.
As well as the star map, a torch covered with red cellophane or one with red LEDs will be very useful. The red light will allow your eyes to remain dark adapted during the evening, yet still allow you to read your map.
Finally, a pair of binoculars can be very handy. If you don’t have binoculars, don’t worry. But if you do, they’re quite useful for seeing some great objects.
You will also need to know a few directions, north, south, east and west. You can find these directions from a compass app on your mobile phone, or just remember, of course, that the sun rises in the east and sets in the west. If the sun is setting at your right shoulder, then you must be facing south.
Another useful direction is the zenith. This is the point directly overhead.
To find your way around the night sky, it helps to know a couple of measurements. 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. A fist held out at arms’ length makes an angle across the sky of about 10 degrees. I’ll be using these measurements during this podcast. A hand span at arm’s length is 15 degrees, and a fist, about 10 degrees.
I will start with discussing the interesting visible stars and constellations in the night sky, and at the end of this podcast, I will add the visible planets and interesting events for October.
Let us begin our tour of the night sky by looking towards the south. If you’re facing south and you look slightly to the right of south, almost to the southwest, you should be able to see two bright stars, one above the other. If you’re in a bright, light‑polluted location, such as central Sydney, they may be the only two stars you can see in that direction. Away from the city and other bright lights, they will be the brightest pair of stars you see towards the south-west.
These two bright stars, one above the other, are known as ‘The Pointer’, the two famous pointer stars which help us find the Southern Cross. The Southern Cross is the best known constellation in the southern sky.
On your star map, the two pointers are clearly labeled. The Southern Cross, however, appears as Crux, which is the Latin name for cross. The brighter of the two pointers is called Alpha Centauri. The other one is called Beta Centauri. Alpha Centauri is the third brightest star in the night sky, and Beta Centauri is the 10th brightest star.
Alpha Centauri is a very interesting star. Although it looks like a single star to your eye, it is, in fact, a group of three, too close together for your eye to distinguish. Through a small telescope, two of the stars are visible. Both are very similar in size and colour to our sun. They’re orbiting about each other. The third star is called Proxima Centauri, and it is the closest star to the Earth, after our Sun.
Proxima Centauri is a red dwarf and is only visible through large telescopes. It is believed to be orbiting the first two stars. Proxima Centauri is about 4.2 light‑years away, or approximately 42 million million kilometres.
I mentioned light‑years. Let me explain what a light‑year is. Light travels incredibly fast, about 300,000 kilometres every second. This means light can travel approximately seven and a half times around the Earth in just one second.
The distances in our Milky Way galaxy and our universe are vast beyond imagining. Light from the Sun takes about eight and a half minutes to reach us. The light from the Moon takes about one and a quarter seconds to reach us. The light from Proxima Centauri takes 4.2 years to reach us. We can say Proxima Centauri is about 4.2 light years away.
This means we see the star as it was 4.2 years ago. A light year is simply a distance, and one light year is about 10 million million kilometers.
Now, let’s get back to the night sky. We’ll return to Alpha Centauri. If you draw an imaginary line downwards from Alpha Centauri, through Beta Centauri, and onward, you will reach the Southern Cross. It’s lying on its right‑hand side, but otherwise it looks just as it does on the Australian flag.
The Southern Cross is very useful, as it can help us find the direction of true south. Hold up your arm, and measure the length of the long arm of the cross using two fingers, from the left‑hand star of the cross to the right‑hand star. Now, measure this distance four times to the left of the cross.
The point you end up at is called the South Celestial Pole, the south pole of the sky. It’s the point in the sky about which all the stars are rotating, but there are no bright stars in this area. It’s just an imaginary point in the sky.
Now, if you drop a vertical line from the South Celestial Pole straight down to the horizon, you’ll find the direction of south on the ground. Here is something interesting you can do if you have a camera that allows you to leave the shutter open. If you take a photograph of the sky to the south, including the South Celestial Pole, and leave your camera shutter for 10 or more minutes, you’ll find beautiful, circular star trails in your photograph.
Now that we can find the South Celestial Pole using the Southern Cross, take your hand span, which is approximately 15 degrees, another two times, so about 30 degrees in the same direction beyond the Celestial Pole position. You should come across a fairly bright star in the southeast of the sky.
This bright star is called Achernar. Achernar is a hot blue‑white star about 144 light years away from us. It represents the end of the River Eridanus in the sky. Eridanus is the sixth largest of the 88 constellations in the night sky, and has been associated with the Nile River, among other rivers.
If you’re in a dark location, well away from city lights, you might have noticed, as you were measuring your hand spans 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 are named after the explorer, Magellan. One of the clouds is slightly larger than the other. This Large Magellanic Cloud, which is about 160,000 light years away, is about halfway down to the horizon from Achernar.
The Small Magellanic Cloud, which is about 200,000 light years away, is just above that. Both clouds are small galaxies that are orbiting our Milky Way galaxy. And they’re gradually being torn apart and absorbed into the Milky Way galaxy.
If you have binoculars, take a look at the Small Magellanic Cloud. You are seeing stars whose light has taken 200,000 years to reach you. Just above the cloud, with your binoculars, you should see a small, fuzzy ‘star’.
In fact, this is not a star. It’s a globular cluster, a ball‑shaped group of several hundred thousand very ancient stars. This one is called 47‑Tucanae. It’s about 16,000 light years away, barely a tenth of the way towards the Small Magellanic Cloud, but still far beyond our solar system.
Let’s turn to the west now. If you’re facing due west, hold out your arm and measure two hand spans, or 30 degrees, above the western horizon. You should reach a bright, orange‑coloured star. If you’re using your star map, rotate it so that the horizon labeled west is at the bottom. This will orient the map to match the western sky in front of you.
Some people have trouble seeing colours in the stars at night. If you don’t see the colour, don’t worry, but you may be able to see it as a reddish or orange colour. It’s also likely to be twinkling, as well, due to the effects of the earth’s atmosphere.
This star is called Antares which means the ‘rival of Mars’ because of its reddish colour. It’s an enormous, red supergiant star, around 400 times the diameter of our sun. If you placed it where our sun is, it would reach out through the solar system and engulf the Earth. It’s a star coming to the end of its life.
Antares is about 604 light years away from the Earth. As a supergiant, it will eventually die as a supernova. However, it’s so far away that this will have no effect on the Earth, although it will be a spectacularly bright sight. Unfortunately, that’s probably going to happen long after any of our lifetimes.
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 it up towards the west with the west horizon at the bottom, as I described earlier, and locate the star Antares on your star map. Just below Antares, you’ll see a short arc of stars which represent the head and shoulders of the scorpion.
Come back up through Antares and above Antares, you should see a large back to front question mark of stars stretching up into the sky above Antares and reaching almost overhead. That’s the tail of the scorpion. At the very end of his tail, you can see his sting quite clearly. Scorpius really does look like a scorpion.
Let’s move on. To the right and above the sting of Scorpius 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 rather triangular teapot. On your star map, Sagittarius is highlighted as the Teapot. Can you see the Teapot pouring tea all over the tail of Scorpius?
Just off the tip of the Teapot is an interesting point in the sky. If you’re away from bright city lights and you’ve been outdoors for more than 15 minutes or so, you might have noticed the Milky Way stretching overhead. It’s a band of faint, milky light stretching from the Southern Cross over on your left up past the two pointer stars and then continuing to stretch over through the tail of Scorpius and, finally, 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 from Scorpio’s sting. It’s a good thing we’re out here near the edge of the Milky Way galaxy and a long way from its centre. At the centre of our galaxy, 27,000 light years away, lies a very large black hole several million times the mass of our sun. We’re quite safe from it here, out on the edge of the galaxy.
Let’s turn to the right again and look to the north. Again, if you’re using the star map, turn it so that north is at the bottom. There are a handful of bright stars in the northern sky and some fairly faint constellations. Let’s begin by looking directly north. Just 10 degrees, or one fist width at arm’s length, above the northern horizon, you should see a prominent star, probably twinkling wildly because it’s so close to the horizon.
This is the star Deneb in the constellation of Cygnus the Swan or, as it’s sometimes called, the Northern Cross. We’ll come back to the constellation Cygnus in a moment.
Just less than two hand spans, or just less than 30 degrees, to the left of Deneb is another reasonably bright star, again, about a fist width or 10 degrees above the horizon. This second star is Vega, the fifth brightest star in the night sky, and it’s in the constellation of Lyra the Harp.
These two stars form the base of a triangle. Above them about three hand spans, or 45 degrees off the horizon, you’ll find the star Altair, which is in the constellation of Aquila the Eagle. Altair may look slightly yellowish in colour. It’s 17 light years away and is about 10 times brighter than our sun and it spins on its axis very quickly, about once every 10 hours. By comparison, our sun only spins once in 25 days.
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 form a noticeable triangle from the Northern Hemisphere. If you ever travel to the north in summer, have a look for the Summer Triangle made of the stars Deneb, Vega, and Altair.
Let’s return to Deneb for a moment. Down by the northern horizon, due north. Deneb is a blue white supergiant star over 100 times the diameter of our sun. Deneb is 3,200 light years away from us, but even at that extreme distance, it still appears as a bright star in our night sky. Up close it would be blindingly bright and if we placed it where the Sun is we would have been incinerated by its intense ultraviolet light that it emits.
As I said earlier, Deneb is in the constellation Cygnus the Swan. If you have your star map aligned with the stars to the north, it will help you 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, another one of the Summer Triangle stars, sits just above Cygnus in the constellation of 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 at a dark site, you’ll be able to see the Milky Way in this region and you’ll see that these two birds, the swan and the eagle, fly along the Milky Way heading south for the northern winter.
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 many bright stars nor any truly distinctive constellations in that direction so let’s leave the eastern sky until next month.
What are the special events and highlights in October 2013? Let’s start with the Moon phases. New moon is on Saturday, 5th of October, at 10:34 AM. First quarter falls on Saturday, 12th of October, at 10:02 AM. Full moon occurs on Saturday, the 19th of October, at 10:38 AM. Finally, the last quarter is on Sunday, 27th of October, at 10:40 AM.
All these times are in clock time, either standard time or daylight saving time as appropriate. Daylight saving begins at 2:00 AM on Sunday the 6th of October. Don’t forget to put your clocks forward by an hour on that night.
What planets are visible in October 2013? Just after twilight, if you turn and face the direction of the setting sun, the west, early in the month of October you should see three planets. The planet Mercury will be on the left, pale and white, and the planet Saturn on the right, brighter and yellowish. Above these is very bright Venus.
Mercury will move from Virgo into Libra at the end of the first week of the month, and then fade into the twilight just before the end of the month. Saturn remains in Libra, but also fades into the twilight during the second half of the month. Venus is visible all month. It begins the month in Libra, then moves through Scorpius, and ends the month in Ophiuchus.
On the 16th and 17th of October, Venus passes close by the bright star Antares. If you have binoculars, Venus will show its phases. At present, it has a half‑moon shape.
On the 7th of October, in the evening, shortly after sunset, there’s a nice grouping of these three planets and the Moon. Mercury and Saturn are low down, Mercury to the left, Saturn to the right. The crescent moon hangs just above them. High above all those shines Venus, very brightly.
In the morning sky, there are two planets, Mars and Jupiter. Both are visible for the whole month in the eastern and north-eastern sky. Jupiter is in the north-eastern sky in the constellation Gemini. It’s easy to recognise as it looks like a very bright yellow star. If you have your binoculars, turn them to Jupiter and watch the dance of its four Galilean moons during the course of the month.
Mars spends the month in Leo in the eastern sky. On both October the 1st and October the 30th, the crescent moon passes just above Mars.
Finally, we have a meteor shower in October. The Orionids are best seen from late evening until dawn and are visible from the first of October until November. The maximum activity is expected is expected around the 21st of October, with hopefully, around 15 to 30 meteors per hour. It’s possible to have a few good viewing nights either side of the 21st. If you get a chance, take your binoculars and a picnic rug and go meteor spotting. Good luck.
If you have enjoyed this podcast and think you might want to regularly check out what’s in the night sky, why not purchase a copy of Sydney Observatory’s book, ‘The Australasian Sky Guide’. It not only contains detailed monthly sky guides, but is jam packed with astronomical information, including rise and set times for the Sun, Moon, and planets, tides and a detailed look at our solar system and upcoming astronomical events.
Only $16.95 from Sydney Observatory, and Powerhouse Museum shops, or you can purchase it online, for which additional costs apply.
You can also subscribe for free to our Sydney Observatory monthly sky guide podcasts through iTunes. For more astronomical information, check our website and blogs at www.sydneyobservatory.com.au. You may also like to explore our Facebook and Twitter accounts. See the observatory website for links to these.
This has been Andrew Jacob from Sydney Observatory with the podcast for October, 2013.