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 (pictured at right), 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. In the evenings in January, you should be able to see the bright planet Jupiter, Venus, Mars and, briefly, Mercury. In the mornings Jupiter and Saturn will be visible, with the gibbous Moon near Jupiter on 8th, and the crescent Moon near Saturn on 16th January.
For this and more, listen to the January 2015 night sky guide audio, or read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a January 2015 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 2015 Australasian sky guide’ – this year the 25th anniversary edition – by Dr Nick Lomb has more information and star maps for months from December 2014 until December 2015 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 2015 monthly sky guide audio
Welcome to the sky guide for January. My name is Nick Lomb. This sky guide can be found on www.sydneyobservatory.com/blog. And then you would 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 will 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 by putting a bit of red cellophane in front of an ordinary torch or you could obtain a small 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 of the states in Australia. So, settle down and look towards the northern sky.
Dominating the northern 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 is 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 the middle of a row. 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. It is a star called Betelgeuse – a giant star, hundreds of times wider than our own Sun.
The name Betelgeuse comes from the Arabic, and 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-fashioned 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 because the constellation was named in the Northern Hemisphere, and we are 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, however, not anywhere 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 its life cycle. Unlike our own Sun, which is converting hydrogen to helium, Rigel is converting helium to 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. Its 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 we reach another bright star, a star called Aldebaran. And that is the brightest star in the constellation of Taurus the Bull.
Aldebaran is a reddish-orange star. Its colour is not quite as obvious as that of Betelgeuse, but it is 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. And it is shining with a brightness about 350 times that of our own Sun. Its 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. And 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, a cluster called the Hyades. The stars of the Hyades are 150 light years away from us.
This particular cluster of stars – the Hyades – are all at the same distance, and 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.
This age for 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 five thousand million years, so 660 million years is relatively recent.
If we go a little bit further along the line that we have 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 one.
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 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 the astronomers measured the velocities, that is how fast the gas and dust was moving, and how fast the stars were moving, they found that the stars and the gas and dust were moving in different directions.
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 of 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 with the mass of the Sun. So it’s exceptionally compact and very dense. So, for example, you could take a match-box 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 first 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 go 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’s 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 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 we 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. Now we turn to the special events in the sky for January 2015. We’ll look at what the planets are doing both in the evening sky and in the morning sky for this month.
In the evening sky, just after it becomes dark, that is, in the evening twilight, the bright planet Jupiter joins Venus and Mars, while the planet Mercury makes just a very brief appearance.
Mercury appears very low in the south-west sky during the first week of the month, close to the very bright planet Venus. It passes just over one moon-width away from Venus on the 10th and 11th January but then disappears back into the twilight in the middle of the month.
Venus itself is very low in the western sky at the beginning of the month and slightly higher later on.
On 22nd January a very thin crescent Moon is below and to the right or north of Venus. Of course that is always one of the highlights of the month when the Moon, and it’s always a crescent Moon, is near the bright planet Venus, and the two of them together are always a very exciting sight in the night sky.
The red planet Mars is low in the west. On 19th and 20th January, it passes one moon-width from the outer planet Neptune. Now, Neptune, being too faint to be seen with the unaided eye, is very hard to find in the sky. But with Mars nearby, it will make it much easier with a pair of binoculars to pick out the planet Neptune. So this is a rare opportunity to see one of the faint outer planets of the solar system and, of course, these days Neptune is regarded as the outermost planet in the solar system so it’s a rare opportunity to see this planet through a pair of binoculars.
On 23rd January, the crescent Moon is below and to the right or north of the red planet, Mars.
The giant planet, Jupiter, appears low in the eastern sky during the second half of the month.
Let us turn to the morning sky for those of you who do rise up in the morning before dawn. You can then see Jupiter in the north-west sky.
On 8th January, the gibbous Moon is to the left or west of Jupiter. On the next morning it’s above and to the right or north.
The ringed planet, Saturn, is in the eastern sky. On 16th January, the crescent Moon is above and to the left or north of Saturn. While on the next morning it is below the planet.
This completes our view of the night sky in January 2015.
If you’d like to know more, this podcast is available each month from the Sydney Observatory website www.sydneyobservatory.com.au.
There are plenty of other posts on the Sydney Observatory blog to make it worthwhile having a look.
And there are regular updates on astronomical happenings, what can be visible in the sky, instruments and artefacts associated with astronomy. Lots of useful information. So it is worthwhile keeping a regular eye on the Sydney Observatory blog which, I repeat, is www.sydneyobservatory.com.au.
We put up these podcasts at the beginning of each month. But if you’d like to know in advance what’s happening in the night sky, and if you’d like to find out in a handy, compact reference form, Sydney Observatory and the Powerhouse Museum publishes a book called ‘The Australasian sky guide’ annually.
So this year it will be the ‘2015 Australasian sky guide’. This is a handy compact reference on what is visible in the southern sky. It gives the rise and set times of the Sun and the Moon, of the planets. It gives information on tides in Sydney It gives information on the solar system, on the constellations and more. And the information is there monthly for the whole year.
And this book is available from Sydney Observatory or the Powerhouse Museum shops, and at good bookshops.
You can purchase it online through the Sydney Observatory website or through the Powerhouse Museum website.
Also, you can visit Sydney Observatory. And January is a great time to visit the Observatory. There are lots of activities happening day or night. And activities are available for all ages whether it’s for young children or adults – there are activities available.
If you look at the website, www.sydneyobservatory.com.au – and that has a galaxy of information about visiting the Observatory day or night. If you would like to come at night, you will need to make a booking. If it’s clear you can look through telescopes. There is a small planetarium – a very exciting little planetarium, and there are 3D movies about relating to astronomy and space.
This has been the view of the night sky in January 2015.
My name is Nick Lomb and this podcast was available through the Sydney Observatory website www.sydneyobservatory.com.au
Irma Havlicek: Just one thing, Dr Nick, I noticed you were a little bit modest about not naming the author of the ‘Australasian sky guide’.
Dr Nick Lomb: OK. ‘The Australasian sky guide’ for 2015, as usual, is prepared by myself, Dr Nick Lomb, and this year’s edition, the 2015 edition of ‘The Australasian sky guide’ will be the 25th anniversary edition for the sky guide.