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 observe the total lunar eclipse of January 31st. Plus a look ahead at the celestial highlights for the year 2018.
See the Sky Chart
We provide a Star Map or January 2018 (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 2018.
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 guide, 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 in this guide.
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 guide 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 meter” 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 guide. 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 guide 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!
At this point, if you are at a dark site away from city or town light pollution and if the Moon is not up, I recommend you wait for about 15-minutes for your eyes to adjust to the darkness. Your view of the night sky will be much better if you do this.
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. It appears as a milky irregular band of light. If the Moon is up or 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. With the help of your star map 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 or maybe yellow-orange. This star represents Orion’s shoulder. It is a red-giant 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 at a late stage 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, perhaps with the help of your star map. 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. From Betelgeuse to Rigel is about a hand span or about 20-degrees across the sky. 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”. What is a light year? It’s a measure of distance, even if it sounds like a time. If you have a torch shine its light into the sky for a moment. The light from your torch travels incredibly fast. In just one second it goes almost 300,000 kilometers. That’s seven and a half times around the Earth or almost the distance to the Moon. In fact in just one and a quarter seconds your torch light would reach the Moon, 380,000 kilometres away. In eight and a half minutes the light would reach the Sun, 150 million kilometres from Earth. After five hours light from your torch would pass Pluto. Finally, after one year of time your torch light will have traveled one light-year of distance. Yet we still haven’t reached the next nearest star!
Proxima Centauri, our closest star after the Sun, is about 42 million million kilometres away from us. Your torch light would take about 4.2 years to reach it. So we can say that Proxima Centauri is about 4.2 light years away from Earth. This also means that we see Proxima Centauri, the star, as it was about 4.2 years ago. We are looking into the past to see everything in the universe.
So a light year is simply a distance, and one light year is about 10 million million kilometers long.
Let’s return to Orion. Orion is a pivotal constellation – its stars are guides pointing to many other interesting stars, constellations and other objects.
If we extend the line of Orion’s belt stars down and right we come to an orange star amongst a V-shaped pattern of fainter stars. From the belt to this orange star is about 20-degrees or a hand span. This group of stars is Taurus the Bull. The orange star is Aldebaran, the eye of the Bull, and his head is the V-shape. A little further down and 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 also known as 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, who holds the sky aloft on his shoulders, and Pleione.
Returning to Orion’s belt we now follow the line of the belt up and to the left, again about 20-degrees. Soon we reach the brightest star in the sky, Sirius, high overhead. 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. With the help of your star map you can identify the shape of the dog, the faithful hunting companion of Orion. Just above Orion, as we lie here, and back towards the eastern horizon 30-degrees from Orion’s belt, is the bright star Procyon in the constellation Canis Minor, the Little Dog. This constellation looks nothing like its name at all – only a few of the 88 constellations in the sky do look like their name.
Returning again to Orion, we now use his sword to direct us to our next destination. You might 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 – it’s a summer compass if you like. Following the direction of the sword far to the North, to the right, brings us to the bright yellowish star Capella, 50-degrees away and just a fist width above the northern horizon. Capella is the brightest star in the constellation Auriga, the Charioteer who was a legendary king of Athens.
Following Orion’s sword to the South, or left, again about 50-degrees brings us past Sirius to a 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 in the sky. The ship was once a single constellation called Argo Navis. But in 1930 Argo Navis was broken up into the keel and the nearby 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 clouds are companion galaxies to our own Milky Way galaxy. But our galaxy is bullying and harassing these smaller companions and tearing them apart. We used to think that in the distant future the Milky Way would absorb both these small galaxies but recent work suggests they are just passing by.
The Small Magellanic Cloud is the lower of the two, that is if you are still lying down with your feet to the west. Just to its right, about 15-degrees, 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 below. 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 the Milky Way is Canis Major and the brightest star, Sirius, followed by 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 superb summer sight!
It’s an even better 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’s 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 then 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!
Now, let’s have a look at the special events and highlights for this month.
What are the special events and highlights for January 2018?
Let me note that all the times I am about to mention are in Eastern Australian Daylight-saving Time (AEDT) as it is properly known. Please make the appropriate adjustments for your time zone and state if necessary.
Let’s start with the Moon phases. We begin the month with a Full Moon on Tuesday 2nd January at 1:24pm, Last Quarter is on Tuesday 9th at 9:25pm, New Moon is on Wednesday 17th at 1:17pm and First Quarter is on Thursday 25th at 9:20am.
The Moon is the brightest object in the night sky when it is up, no matter what phase it is in. It is well worth observing its changing phases or looking closely at the craters, plains and other features with binoculars or a telescope. But to get the best views of the Milky Way and the constellations it is best to avoid moon-lit hours. If the Moon is between New and Full (i.e. waxing or ‘getting bigger’) wait for it to set before observing the Milky Way and stars. If the Moon is between Full and New (waning or ‘getting smaller’) observe before it rises. You don’t need a daily list of rise and set times – just watch the Moon for a few days and you will soon learn to predict its behaviour.
What planets are visible in January 2018?
There are no planets visible on January evenings this year.
In the morning, however, Mercury, Mars, Jupiter and Saturn are visible. Mercury is low in the south-east during the morning twilight, moving from Ophiuchus into Sagittarius during the month. On the 13th and 14th Mercury and Saturn are close – less than two Moon-widths apart – Mercury is the brighter of the two and Saturn appears yellowish. And on the 15th a thin crescent Moon joins the two planets. This is a good opportunity to identify Mercury.
Mars is in Libra rising around 1-2am this month. It is close to Jupiter on the 7th, only half a Moon’s-width away. On the 12th the crescent Moon joins Mars and Jupiter, sitting just below them.
Earth reaches its closest point to the Sun, or perihelion, on Wednesday 3rd January at 4:35pm. We will be just over 147 million kilometres from the Sun.
What other celestial events are happening in January 2018?
The highlight of the month is a total lunar eclipse, the first of two this year, on Wednesday January 31. It is quite safe to watch in its entirety – unlike a solar eclipse. This lunar eclipse will be visible across Australia and New Zealand and it is the first total lunar eclipse visible from these locations since 2015. The times for the various parts of the eclipse vary depending on your location and whether your state follows daylight saving time. I will provide the times for Sydney and NSW and for other locations please check the table in the transcript of this podcast.
For those in NSW the eclipse effectively begins as the Moon moves into the darker part of Earth’s shadow – the umbra. This occurs at 10:48pm (remember these are daylight-saving times). It is fully eclipsed from 11:51pm on the 31st Jan to 01:08am on Feb 01. The eclipse ends at 02:12am when the Moon finally leaves the umbra.
For other locations Table 1 gives times.
When the Moon is totally eclipsed it turns a reddish colour. This is caused when sunlight passing through Earth’s atmosphere is bent, or refracted, into the umbral shadow. Blue light is scattered out – just as it is at sunset – leaving only red light to reach the Moon. From the Moon you would see Earth surrounded by a ring of red sunsets! Noone has yet seen this from the surface of the Moon.
But is this red moon also a blue moon?
The modern definition holds that a “blue moon” is the second full Moon in a calendar month. Of course it doesn’t actually look blue and I’ll leave the complexities of the definition for another blog post. But looking at the table of eclipse times you can see that in New Zealand it is NOT a blue moon. In NSW, the ACT, Victoria and Tasmania it is also NOT a blue moon, but only because daylight-saving time pushes the full Moon into the early morning of February 1st. In South Australia it IS a blue moon, but only just, despite daylight-saving being in place. In Queensland it IS also a blue moon, this time because daylight-saving isn’t recognised. And finally in WA and the Northern Territory it IS a blue moon, and would be even if daylight-saving were recognized, which it is not.
Phew! So a red moon can also be a blue moon, but it depends where you are and who has won the battle on daylight-saving in your state!
Let’s move on! It’s the beginning of the year so here are a few good celestial events to look out for in 2018: there is another blue moon in March (for everyone in Australia but not New Zealand this time); in February there is a very marginal partial solar eclipse if you live in southern Victoria, SA or in Tasmania; in July and again in October all five naked-eye planets will be visible at once in the evening sky; the Geminids meteor shower occurs once again in December; and the big astronomical event for 2018 is Mars – in July and August it will be closer and brighter, and look larger through a telescope, than it has at any time since 2003. For added effect the year’s second total lunar eclipse on July 28 places a red Moon close to red Mars in the sky. Don’t miss it!
There is one last event I want to mention before finishing. On June 5 Sydney Observatory turns 160. We celebrate the birthday on the anniversary of the day the time ball, atop the Observatory’s tower, was first dropped – way back in 1858.
And that wraps up the special events for January 2018.]
These monthly Night Sky Guides are available from the Sydney Observatory website or from iTunes. An excellent companion is the annual “Australasian Sky Guide” book written 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, plus tide times and a detailed look at our solar system and upcoming astronomical events. It’s only $16.95 from Sydney Observatory or the MAAS store, or you can purchase it online, for which additional costs apply.
For more astronomical information, why not check the Sydney Observatory website and blogs, and keep in touch via our Facebook and Twitter accounts.
And if you’re in Sydney visit the Observatory in the Rocks area. Join a tour to view the skies through our telescopes – day or night. 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, some require bookings and some run only during school holidays.
And that brings to an end this Night Sky Guide from Sydney Observatory and from me, Andrew Jacob. Thank you for listening and I wish you clear skies until next time.