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 Nick Lomb, Sydney Observatory’s Curator of Astronomy.
Nick takes us on a tour of the stars and constellations prominent in the January sky, including Betelgeuse and Rigel in Orion, Aldebaran in Taurus, and Sirius, the brightest star in the night sky, in the constellation Canis Major. He also tells us which planets are visible in the evening and morning sky in January.
For this and more, listen to the January 2013 night sky guide audio, or read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a January 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.
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).
READ THE TRANSCRIPT (after the jump)
Transcript of the January 2013 monthly sky guide audio
Welcome to the Sky Guide for January. My name is Nick Lomb. I’m the curator of astronomy here at Sydney Observatory. This sky guide can be found on www.sydneyobservatory.com.au and then you will need to go to the ‘astronomy’ tab, which is on the far right of the web page. We’ll start off the sky guide by touring the stars visible this month. In the second part of this podcast, we’ll consider planets and other special events like eclipses and the position of the planets happening this month.
Before starting the tour of the night sky, if possible, download the star map that’s available from this website. It is available each month. Then take it outside. Make sure you know the cardinal directions: north, south, east and west.
And ideally, you should have a torch with a red light, so you can have a torch with a red light by putting a bit of red cellophane in front of an ordinary torch, or you could obtain a red LED torch from an astronomy supply shop. The idea of the red torch is you can look at the stars without wrecking your adaptation to the night sky. So you can look at the star map and look up at the sky and see both.
Let us start our tour of the night sky, and start off by facing north in the late evening. And, of course, in January, it does not become dark until fairly late, at least in most states of Australia. So settle down and look towards the northern sky.
Dominating the north sky is the familiar constellation of Orion. This is always a welcome signpost for the Australian summer sky. It’s quite an unmistakable constellation. It’s high up in the northern sky, almost due north in the evening, and it can be recognised as it has four stars in a rectangle and three stars in a row in the middle. These three stars in a row are Orion’s Belt.
The star on the lower right of the rectangle is a reddish star, one of the few stars in the sky that you can actually recognise its colour. The star called Betelgeuse, a giant star, hundreds of times wider than our own Sun. The name Betelgeuse comes from Arabic. It means the armpit of the giant. So although it sounds like a very exotic name, in fact it means something very mundane. It describes the location of the star in an old fashion drawing of the constellation.
You may ask why Orion’s armpit is at the bottom of the constellation and not at the top. The reason is the constellation was named in the northern hemisphere and we’re looking at it from the southern hemisphere. So poor Orion has his head down and his legs above his head, not I would imagine, a comfortable position.
The star diagonally opposite Orion is another bright star, but without Betelgeuse’s red colour. It’s a star with a bluish-white colour, a star called Rigel. This is also a very bright star, but is not anywhere near as large as Betelgeuse.
It’s a long way from us. It is 775 light years away. That is, light from this star has taken 775 years to reach us. Or we could say that the light that we see from Rigel left it back in the 1200s or the 1300s, which of course is a very long time ago.
Rigel is a star that is fairly late in it’s life cycle. Unlike our own Sun, which is converting hydrogen to helium, Rigel is converting helium into carbon and to oxygen. Stars use that kind of fuel only at a very late stage of their life cycle.
The star is fairly hot. It’s temperature is 11,000 degrees Celsius, very much hotter than the outer surface of our own Sun, which is around 5,500 degrees. Rigel has a distant companion as well, that is, a star circling around it, but it’s a long way away from the main star of Rigel.
One of the many nice things about looking at Orion is that it can be used as a signpost to find other stars and star groupings in the sky. Let us extend a line through the three stars of Orion’s Belt, that is the three stars in a row, towards the left. That is, towards the west, and reach another bright star, a star called Aldebaran. That is the brightest star in the constellation of Taurus the Bull.
Aldebaran is a reddish-orange star. It’s colour is not quite as obvious as that of Betelgeuse, but it’s still not the usual white colour that we can see for most stars in the sky. Aldebaran is a giant star, about 40 times as wide as our own Sun. It is shining at a brightest about 350 times that of our own Sun. It’s distance from us is 65 light years. That is, the light that we see left it 65 years ago.
Aldebaran is in a group of stars that forms an upside down V in the sky. Looking for those stars is the easiest way to find the constellation of Taurus the Bull and Aldebaran. What is interesting is that the V shaped group of stars are much further away than Aldebaran. Aldebaran is actually between us and the other stars in the group. The stars in the group are all part of one cluster called the Hyades. The stars of the Hyades are a 150 light years away from us.
The stars of this particular cluster of stars, the Hyades, are all at the same distance. They all move in the same direction in the sky. They all formed at the same time. Because of their geometric properties and the properties of the individual stars, astronomers can actually determine the age of that cluster of stars.
The age of the stars of the Hyades turns out to be 660 million years. This may sound like a long time compared to human lifetimes, but in fact it’s quite recent at least in astronomical terms. Our own Sun has an age of something around 5,000 million years. So 660 million years is relatively recent.
If we go a little bit further along the line that you’ve extended from Orion’s Belt towards the left, that is towards the west and past Aldebaran…So if we extend it a bit further we reach another compact group of stars that are called the Pleiades. The Pleiades are the most famous star cluster in the sky. This group of stars provides a very good test of eyesight. Most people can see six stars, but those with very good eyes can also see a fainter seventh star.
There are many legends and stories associated with these stars. According to Greek mythology, they are the Seven Sisters. The story is that something happened to the seventh sister and that is why it’s much fainter than the other six.
There are similar stories told by the Australian Aboriginal people. According to one group of stories, they are the seven ancestral women. One of these women fell in love with two spirit men on Earth and stayed behind, while the other six returned to the sky. The one sister and the two spirit men became the parents of everything on Earth, the originators of everything else on Earth.
Through a telescope, many more than seven stars can be seen, hundreds of stars. Photographs of the stars show that there are bits of gas and dust floating around many of the stars in the cluster. It was first thought by astronomers that these bits of gas and dust are the remnants of the gas and dust from which the cluster of stars, the Pleiades, originally formed.
However, when astronomers measured the velocities, that is, how fast the gas and dust was moving and how fast the stars were moving, they found the stars and the gas and dust were moving in a different direction. So there is no connection between the gas and dust and the stars. It seems that the stars have just bumped into this cloud of dust, and they’re moving through it.
Now let’s extend Orion’s Belt in the opposite direction. We first extended it towards the left, towards Aldebaran and further towards the Pleiades. Now let’s extend it towards the right, towards the east and upwards until we reach Sirius, the brightest star in the sky. Sirius is also the brightest star in the constellation of Canis Major, the great dog. Occasionally Sirius is referred to as the Dog Star.
It’s the brightest star in the sky, so it’s worth becoming familiar with its brightness, because if you see anything brighter than Sirius in the sky, it’s likely to be a planet like Jupiter or Venus. Venus, of course, can be the brightest object in the night sky apart from the Moon.
One of the interesting things about Sirius is that it has a companion star, a very faint companion star called by astronomers by the name Sirius B. Not an exciting name, but it’s a simple way of separating the object from the main star.
Although it does not have an exciting name, it is a very exciting object because Sirius B is very compact, exceptionally compact and also very faint. Astronomers consider that it is a white dwarf star, a star about the size of the Earth, yet at the same time the mass of the Sun. So it’s exceptionally compact and very dense.
So, for example, you could take a matchbox amount of material from Sirius B and you would not be able to lift it. It would take several cranes because its mass would be several tons. This companion star is very hard to detect because it’s overwhelmed by the brightness of the main star, Sirius A. It was first detected back in the 1840s by an astronomer called Friedrich Bessel. He noticed that there was a slight wobble in the motion of Sirius. That wobble was due to a companion star circling around the main star, Sirius A.
Sirius B was finally seen by the optician Alvan Clark in the United States in 1863. Clark was testing a new telescope that he was building, a very large telescope. He tried it out on Sirius, as it is the brightest star in the sky.
While he was trying it out, he noticed there was a faint object next to the bright star of Sirius, and that is the faint white dwarf star, Sirius B. It takes 50 years to circle around the main star. The two stars were closest together in 1994, and they’ll be furthest apart in 2019. So over the next few years, it will be easier to tell them apart, and it will be easier to see Sirius B.
Let us now go, briefly, to the southern part of the sky, so turn around and face south. The Southern Cross is in the south-east. It is on its side at this time of the year. The way to recognise the Southern Cross is that there are two Pointer stars, Alpha and Beta Centauri, directly below.
It is important to look for Alpha and Beta Centauri because the Southern Cross can be easily confused with another group of stars a little higher up in the sky which astronomers call the False Cross. The real Southern Cross is much more compact and has the two Pointer stars directly below, pointing to the stars in the Southern Cross.
Let us use the Southern Cross as a signpost and take a line from the star on the left of the cross and the top star of the cross, and take a line upwards and reach a very bright star almost overhead, a star called Canopus. That is the second brightest star in the sky, almost as bright as the star Sirius.
This completes the guide to the stars in the January night sky. We’ll continue with the second part of this podcast, talking about the planets and other phenomena and special events that are happening in the January night sky.
This is a description of the planets and other events happening in January 2013. On the 2nd of January at 4:00pm Australian Eastern Summer Time, the Earth is closest to the Sun. That is referred to by astronomers as perihelion, the Earth has reached its closest point to the Sun. We’re not necessarily warmer or the temperature is not necessarily hotter because we’re closest to the Sun, but of course it is summer. But summer and the other seasons are due mainly to the tilt of the Earth’s axis.
But because we’re closer to the Sun in January it does mean that the Earth is moving faster around the Sun, and consequently, our summers are shorter because of that…because the Earth reaches perihelion in January.
With regard to the planets, there are two planets visible in the evening sky, Mars and Jupiter. Mars is very low in the western sky in the constellation of Capricornus, while Jupiter is in the northern sky in the constellation of Taurus, the bull. It is below and to the left, or west, of the bright star Aldebaran.
On the 14th of January, a thin crescent Moon is to the right, or north, of the planet Mars. A week later, on the 22nd of January, the gibbous Moon is to the right, or east, of Jupiter. There will only be 3.5 degrees, or seven moon-widths, separating the Moon and Jupiter at that time.
In the mornings, for those of you who rise in the early mornings, there are two planets visible, Venus and Saturn. Venus, which is, of course, extremely bright, is low in the east and it’s moving from the constellation of Ophiuchus to Sagittarius during the month.
On the 11th of January, a very thin crescent Moon is just below Venus and, of course, that may be a challenge to see, because the Moon will be such a thin crescent at that time.
Saturn is in the east above Venus. On the 7th of January, the crescent Moon is above Saturn. That should be a very nice sight to see.
This completes the guide to the night sky in January 2013. Do not forget, if you’d like to get more information about what’s visible in the night sky, you can purchase a copy of the ‘Australasian Sky Guide’ that I produce each year for Sydney Observatory.
You can buy it personally from Sydney Observatory or the Powerhouse Museum or you can buy it online from www.sydneyobservatory.com.au. Click the ‘bookshop’ tab at the bottom of the page. The price is a very reasonable $16.95, or it’s a little bit more if you’re buying it online, so as to cover postage and handling.
You can subscribe to these podcasts through iTunes. Just search for ‘Sydney Observatory monthly sky guides’. If you search just for ‘Sydney Observatory’, you’ll find not only our free monthly sky guides, but also a self-guided walking tour app that for $1.99 will guide around Sydney Observatory, round the grounds of Sydney Observatory, Observatory Hill, which overlooks the beautiful Sydney Harbour, it will then guide you onto the Harbour Bridge and through the historic Sydney Rocks area.
Sydney Observatory is open for booked night visits. Those visits include a visit to our telescope domes and the telescope view of the night sky on nights where clouds permit. On cloudy nights, Sydney Observatory offers a mini planetarium session instead.
Sydney Observatory is also open on just about every day during the year from 10:00am till 5:00pm. You can visit in the daytime without any booking and it’s free. You can look around the exhibits and the grounds at no charge. There are charges if you take part in a staff-led daytime program.
Information on all this is available on www.sydneyobservatory.com.au. Click on the ‘astronomy’ tab at the top right and then choose the monthly sky guides on the left side bar for the sky guides.
This has been Nick Lomb, Sydney Observatory Curator of Astronomy, with the January 2013 night sky podcast.