To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map each month. This month’s guide is presented by Dr Andrew Jacob, Sydney Observatory’s Curator of Astronomy.
This month, learn how to find the summer constellations of Orion, Canis Major and Taurus. Tour the Milky Way galaxy from the Southern Cross to Auriga in the north and discover the brightest stars in the sky. Andrew also tells us how to find the planets Venus and Mercury in the evening sky. And what are the celestial highlights to look out for during the year of 2017.
See the Sky Chart
We provide a January 2017 night sky map (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.
Read the Guide
Hello, and welcome to the night sky for January 2017.
This is Andrew Jacob, and I’m the Curator at Sydney Observatory, part of Sydney’s Museum of Applied Arts & Sciences. Come on a tour of the night sky with me. Learn what stars and constellations are visible, where to find the planets and what special events are happening overhead this month.
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 a free one from Sydney Observatory’s website where you’ll find it in the ‘Astronomy Resources’ section under ‘Monthly Sky Guides’. The star map will show you what stars and constellations are visible in the night sky this month and I’ll be referring to that star map during this podcast.
As well as the star map, a torch with a red LED, or one covered with a few layers of red cellophane, 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 star map.
Finally, a pair of binoculars or a telescope can be very handy. They’re not essential for following this podcast but if you do have them they will help you see a few of the fainter objects more easily and in more detail.
Now that we have our equipment together we need to know a few directions and also how to measure angles across the sky.
You can find the cardinal directions – North, South, East and West – from a compass app on your mobile device, or just remember, of course, that the Sun rises in the east and sets in the west. And if the Sun is setting at your right shoulder, then you must be facing south. Another useful direction to remember is the zenith. This is the point directly overhead.
To find your way around the night sky, it helps to know how to measure angles across it. It makes no sense to say, for instance, that one star is “2 centimetres” to the left of another or that a shooting star left a trail “half a metre” long! Instead we should use angular measurements. The distance around the horizon, from North, through East, South, West and back to North is 360 degrees. And from the horizon vertically upwards to the zenith overhead is 90 degrees.
But how do we measure smaller angles? Well, despite the great variety of human form our fingers, hands and arms are all pretty much in the same proportions. If you hold your hand out at arm’s length and stretch out your little finger and thumb to make a hand span, they span an angle across the sky of about 20 degrees. A fist held out at arm’s length makes an angle across the sky of about 10 degrees. And a finger held up at arm’s length is about 1 degree, or twice the width of the Moon or the Sun. I’ll be using these measurements during this podcast. So, a hand span at arm’s length is 20 degrees, a fist is about 10 degrees, and a single finger is about one degree across the sky.
One final point to note before we get started. The Earth rotates and so the sky changes hour by hour. My descriptions of the constellations and stars in this podcast fit the time of one to two hours after sunset.
This month the best constellations and stars are high overhead. So let’s begin by getting comfortable – grab a blanket, lie down with your feet facing west and look straight up towards the zenith. With your feet pointing westwards most of the constellations above will appear upright, rather than upside down as they often do from the southern hemisphere!
If you are in a dark location, and there is no Moon up, you will see the Milky Way, the edge-on view of our own galaxy, stretching from the south horizon on your left, passing overhead through or close to the zenith, and reaching the north horizon on your right. If you are near a city or large town and light pollution affects your view the Milky Way won’t be visible but you will still see a band of bright stars stretching across this part of the sky, from south to north.
We begin with the constellation Orion, the Hunter in the sky, slightly north or right of the zenith. Locate the three stars of Orion’s belt. From top to bottom these are Alnitak, Alnilam and Mintaka. To the right is the star Betelgeuse, glowing orange-red. This enormous star represents Orion’s shoulder. It is a star coming to the end of its life, it is 425 light years away and it’s hundreds of times larger than our Sun.
To the left of Orion’s belt is the bright star Rigel, one of Orion’s knees. Rigel is also late in its life cycle, although not as late as Betelgeuse. It is about 1000 light years away and its surface temperature is about 11,000 degrees Celsius – about twice as hot as our Sun.
Now, if Betelgeuse and Rigel form Orion’s right shoulder and left knee respectively you should now be able to imagine the figure of a man. His head and shoulders are to the right, his body narrows to the three “belt stars” at his waist and his legs stretch out to the left. Between Orion’s legs, hanging from his belt, is Orion’s sword. To your eye this appears as a line of three fuzzy stars. Through binoculars they appear as three groups of stars, with the middle one surrounded by a faint hazy “cloud”. This cloud, or nebula, is the Orion Nebula, over 1500 light years away. It is also known to astronomers as “M42”. It is perhaps the most photographed object beyond our solar system and is a large cloud of, mostly, hydrogen gas which is producing new stars. The cloud is 15 light years in diameter and the stars you see embedded within it (with your binoculars) were formed from the collapsing hydrogen gas within the last million years or so.
A moment ago 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 could travel approximately seven and a half times around the Earth in just one second.
The distances in our Milky Way galaxy and the universe are vast beyond imagining. Our Sun is 150 million kilometres from the Earth. And it takes light about eight and a half minutes to reach us from the Sun. Our Moon is almost 400 thousand kilometres from the Earth and it takes light from the Moon about one and a quarter seconds to reach us. Proxima Centauri, our closest star, is about 42 million million kilometres away from us. Its light takes about 4.2 years to reach us. So we can say that Proxima Centauri is about 4.2 light years away from us.
It also means that we see Proxima Centauri the star as it was 4.2 years ago. We’re looking into the past to see everything in the universe. A light year is simply a distance, and one light year is about 10 million million kilometres long.
Let’s return to Orion. Orion is a pivotal constellation – its stars are guides pointing to many other interesting constellations.
If we extend the line of Orion’s belt stars down and right we come to a bright orange star amongst a V-shaped pattern of fainter stars. This is Taurus the Bull. The orange star is Aldebaran, the eye of the Bull, and his head is the V-shape. A little further to the right, still following the line of Orion’s belt stars is a small cluster of sparkling diamond-like stars. Best seen through binoculars, not a telescope, these are the Pleiades or Seven Sisters. It’s a group of young stars all born from the same nebula – so they really are sister stars – these represent the daughters of Atlas and Pleione.
Returning to Orion’s belt we now follow the line of the belt to the left and up. Soon we reach the brightest star in the sky, Sirius. Its name means “scorching” or “brilliant” and you can see why. Sirius is also called the “Dog Star” because it’s the brightest star in the constellation of Canis Major, the Big Dog. Use your star map to identify the shape of the dog, the faithful hunting companion of Orion. Just above Orion is the bright star Procyon in the constellation Canis Minor, the Little Dog.
Returning again to Orion, we now use his sword to direct us to our next destination. You will notice Orion’s sword points directly left (South) and right (North). This is a very useful thing to remember when the Southern Cross is low in the sky as it is this month. Following the direction of the sword North, to the right, brings us to the bright yellowish star Capella, just a fist width above the northern horizon. Capella is the brightest star in the constellation Auriga, the Charioteer and a legendary king of Athens.
Following Orion’s sword to the South, or left, brings us past the zenith and to another bright, white star. This is Canopus, 205 light years away and the second brightest star in the night sky after Sirius. Canopus is one of the celestial navigation stars used by ships navigators for centuries. Appropriately it’s the brightest star in the constellation Carina, the Keel of the ship. Nearby are the sails, Vela, the rear deck, Puppis, and the ship’s compass, Pyxis. This is not an easy ship to identify in the sky – perhaps it’s fading into a summery ocean haze?
More easily identified is the False Cross. This is an “asterism” or star-shape not one of the 88 formal constellations. It lies on the border of Carina and Vela taking in stars from both constellations. It is larger and fainter than the real Southern Cross which lies further to the left and very close to the southern horizon.
Let’s look back to Canopus. Below this star you will notice, if you are in a dark site away from city lights and with no Moon in the sky, two cloudy patches. These are the Large Magellanic Cloud (LMC on your map) and Small Magellanic Cloud (SMC). These are two companion galaxies to our own Milky Way galaxy. But our galaxy is bullying and harassing these smaller companions, tearing them apart and in the distant future the Milky Way will absorb both these small galaxies.
The Small Magellanic Cloud is the lower of the two, if you are still lying down with your feet to the west. Just to its right is another bright star. This is Achernar, meaning the River’s end. It is the star at the end of the constellation Eridanus, the River in the sky. Now here’s a small challenge for you – can you trace the river Eridanus across the sky? It meanders from Achernar across the zenith to its source near the star Rigel in Orion. Use your star map to “star hop” from one star to the next along the course of the river, travelling upstream to Orion. This “star-hopping” technique is a good one to practice for future use when trying to find faint or obscure celestial objects, particularly with your binoculars or a telescope.
Let’s review what we’ve seen tonight. We begin from the South, on your left, and we’ll travel along the Milky Way. Close to the southern horizon is the Southern Cross, with the Two Pointer Stars nearby. Moving northwards, to the right, we pass the False Cross between Vela the Sails and Carina the Keel. Then comes Canopus, the navigation star, and below it the Magellanic Clouds and Achernar. Next along is Canis Major and the brightest star, Sirius, followed by the Orion the Hunter and his belt and sword. Then comes Taurus the Bull and the Seven Sisters and finally low down on the northern horizon is Capella in the constellation Auriga. Phew! What a grand sight!
It’s an even grander sight with binoculars. If you sweep the Milky Way passing all the objects I’ve mentioned tonight you’ll also discover, in between, hazy gaseous nebulae where stars are born, sparkling clusters of young stars and curious star patterns here and there. At first it seems overwhelming but if taken in bite sized chunks, month by month, there is a lifetime of observing to be done.
But wait there’s more! Most of the brightest stars in the night sky are visible during January nights. Sirius, the Dog Star is the brightest followed by Canopus, the navigation star. Third brightest is Alpha Centauri, one of the Two Pointers low in the south. Next are Arcturus and Vega, neither visible on January evenings. Sixth brightest is Capella, a fist-width above the northern horizon, and Rigel, Orion’s knee. Next is Procyon in the Little Dog. Ninth is Achernar at the end of the River Eridanus. Finally, Betelgeuse, Orion’s shoulder, is the tenth brightest star in the night sky. That’s eight of the ten brightest stars all visible at once on these warm summer evenings – January is truly one of the best months to be outdoors journeying through the starry realms!
What are the special events and highlights for January 2017?
Let me note that all the times I am about to mention are in Eastern Australian Daylight-saving Time or AEDT as it is properly known.
Let’s start with the Moon phases. We begin the month with a First Quarter Moon on Friday 6th January at 06:47am. Full Moon occurs on Thursday 12th at 10:34pm. Last Quarter is on Friday 20th at 9:13am. Finally New Moon is on Saturday 28th at 11:07am.
What planets are visible in January 2017?
The evening planets this month are Venus and Mars. Venus, unmistakably bright as the Evening Star moves from Aquarius into Pisces getting lower in the sky each night. On January 2 the crescent Moon is very close by. Through a telescope Venus initially appears as a hemisphere, or at half phase. By the end of the month it grows larger, as it is approaches Earth, and becomes crescent shaped.
Mars, much fainter than Venus and above and to the right of Venus throughout the month, also descends each night. It moves from Aquarius to Pisces. The crescent Moon is just to the right on January 3rd – one of the highlights of the year.
In the morning this month we can see Mercury, Jupiter and Saturn. Mercury begins the month low in the east in Sagittarius. As usual it is difficult to spot but the crescent Moon assists, sitting just to its left on Australia Day.
Jupiter is high in the north-east in Virgo. And Saturn is low in the east but above Mercury for the month and in the constellation Ophiuchus.
Earth reaches its closest point to the Sun, or perihelion, on Thursday 5th at 1:18am. It will be just over 147 million kilometres from the Sun.
What else is happening in January 2017?
January and February are good months to observe a variable star. All stars change brightness to some degree but mostly this is not apparent to your eye or even through binoculars. However, one star, Mira, clearly brightens and fades over the course of almost a year. Mira is in the constellation Cetus the Whale and has come to be known also as “Mira the Wonderful” for its behaviour. It’s highlighted on your star map and if you were successful at star-hopping along Eridanus you should have little trouble locating it. In early January it will not be visible to the naked eye but during the month it brightens. By February it should be clearly visible to your eye. Then as March arrives it fades towards invisibility again. Incidentally 2017 marks the 400th anniversary of the death of the man who, in modern times, is credited with discovering Mira’s variability. David Fabricius saw Mira brighten in 1596 but even he wasn’t expecting it to regularly brighten and fade so it was almost a decade before its regular variability was recognized – and it then became known as the Wonderful.
This year also marks 200 years since the death of Charles Messier. Messier was searching for comets and to distinguish them from other fuzzy, comet-like objects in the sky (like nebulae and star clusters) he made a list of just over one hundred fixed objects. One of them was the Orion nebula, hence its alternative designation as Messier object number 42, or M42.
While we are at the beginning of the year I should mention a few good celestial events to look out for in 2017: the Eta Aquariid meteor shower occurs in May and the Geminids in December. Both are worth waiting up for this year; there is a partial eclipse of the Moon visible across Australia in August; and Venus and Jupiter are close in the dawn sky in November. And the biggest event this year will be the total solar eclipse in August, overnight on the 21st-22nd for Australia. This will be visible from the USA but not from Australia. Expect to hear much more about this!
And that wraps up the special events for January 2017.
An excellent companion to this sky guide is the annual Australasian Sky Guide book by Dr Nick Lomb. It not only contains detailed monthly sky maps, but is jam packed with astronomical information, including rise and set times for the Sun, Moon, and planets, tide times and a detailed look at our solar system and upcoming astronomical events.
The Australasian Sky Guide for 2017 is available now, still for just $16.95, from Sydney Observatory or the Museum of Applied Arts & Sciences (MAAS) stores. It’s also available online via the Museum of Applied Arts & Sciences website, for which additional costs apply.
And if you’re in Sydney visit the Observatory in The Rocks area. View the skies through our telescopes (day or night and weather permitting), visit our Space Theatre or the Sydney Planetarium. Tour our exhibition and discover the history of Australian astronomy. But please check our website as not all the activities are free and some require bookings.
This brings to an end this Night Sky podcast from Sydney Observatory, and from me – Andrew Jacob. Thank you for listening and I wish you clear skies until next time.