To help you learn about the southern night sky, Sydney Observatory provides a written guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory’s Astronomy Programs Coordinator.
Mel guides you to find the constellations, Orion, Scorpius and Crux (the Southern Cross), along with related ancient Greek and Australian Indigenous astronomical mythologies. She also helps you find some star clusters, including the Jewel Box. And she tells us what to look out for in the May skies.
There’s a lot happening in our sky this month, so read the transcript below for more details.
SEE THE SKY CHART
We provide an embedded sky map below (please be patient as it can take a little while to load) and a May 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’, 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 GUIDE (after the jump)
Hello and welcome to the night sky guide for May. My name is Melissa Hulbert and I’m an Astronomy Programs Coordinator at Sydney Observatory.
Before we start our night sky tour, make sure you download the May sky map from our website at www.sydneyobservatory.com.au. Click the Astronomy tab, and go to the Monthly sky guides section.
Armed with your sky map and a small torch with some red cellophane covering it, find a nice dark place away from the glare of the street lights and make sure you know your cardinal directions – north, south, east and west. Remember that the Sun rises in the east, moves through the northern sky during the day and sets in the west; or a small compass will also point you in the right direction. Pick a comfortable spot either on a rug or a deck chair that you can lay back in. Wait about 5-10 minutes and allow your eyes to adapt to the darkness.
Now turn towards the west. Low in the western sky is the familiar constellation of Orion, the Hunter. In Greek mythology, Orion was a hunter of great skill and boasted that he could kill all living animals. Gaea, the Earth goddess, was alarmed by his statement and fearing for all the animals on Earth she sent a scorpion to kill him. Orion was stung on the shoulder but was revived and placed in the stars along with the scorpion. This entire myth is played out in the stars each year. As Scorpius the Scorpion rises in the east, Orion sets in the west, defeated. When Scorpius sets in the west the healer Ophiuchus crushes the Scorpion into the Earth and revives Orion so he can rise in the east again. Orion appears in many cultures, even the ancient Egyptians saw Orion as Osiris, god of the underworld and of regeneration.
If you’re having difficultly picking out the Hunter then look for ‘The Saucepan’. This is a familiar group of stars for those of us in the southern hemisphere and is Orion’s belt and sword. Orion is now on his side as he sets below the western horizon.
Now turn to face the east and there is Scorpius rising in triumph as Orion sets defeated for another season.
The Scorpion is one of the easiest constellations to pick out as it is one of the few that does look like what it’s supposed to represent. It covers about 30 degrees in the sky. Working out degrees in the sky is quite easy. Hold your arm out towards the sky and make a fist. From one side of your fist to the other, this is 10 degrees. Hold your other arm out and spread your hand out as wide as you comfortably can (so the opposite of a fist), from your little finger to your thumb is 20 degrees. Put your hands side-by-side and you now have 30 degrees, the size the Scorpion covers in the sky. This does work for everyone, as your arm length is proportional to your hand size.
Now, look for the Scorpion’s heart, Antares, a red supergiant that is 400 times the diameter of our Sun. Antares means ‘rival of Mars’, and when they are close together in the sky they certainly do look very similar.
If you have a pair of binoculars, then near Antares is a small globular star cluster, M4, which is a group of old stars that lies about 7,000 light years away, making it one of the closest globular clusters to us. Below the sting of the Scorpion are two open star clusters, M7 and M6, which are also worth a look. See if you can see the butterfly in M6. These names I’m giving the clusters are catalogue names. M stands for Messier and is named after Charles Messier, an 18th century French comet chaser. He made a catalogue of 103 fuzzy objects that were not comets so that he didn’t waste his time looking at them. Other astronomers later added a few more objects to the catalogue bringing the total to 110.
Time to turn and look towards the south. High in the southern sky is the constellation Crux, better known to us as the Southern Cross. Crux is Latin for cross. The Southern Cross, like the Scorpion, is another constellation that does look like what it’s supposed to represent. It is surrounded on three sides by the constellation Centaurus, and the two brightest stars in Centaurus make up the Pointers which point to the Southern Cross and this is one way to check you have the right cross as there are many stars in the southern sky that look like crosses. During May the Pointers are to the east and slightly south of the Southern Cross.
The second brightest star in Crux is a marker for a wonderful binocular and telescope object. To find the 2nd brightest star, whose name is Mimosa, look for the star in Crux closest to the Pointers. Now just nearby – at about 7 o’clock if you imagine a clock face over Mimosa, is a wonderful open star cluster called the Jewel Box. It looks like a sideways ‘A’. In a telescope, wonderful colours can be seen with white stars and a red supergiant. Sometimes even green appears but of course there are no green stars – this is just an illusion. The famous 18th century astronomer John Herschel gave the cluster its name as he likened it to a piece of multi-coloured jewellery.
Crux sits within one of the arms of our Milky Way and if you are away from the city lights you will see this arm and notice a dark patch between the brightest and second brightest stars of this constellation. This dark patch is called the Coalsack and is a dark nebula – lots of gas and dust that are blocking out the background stars.
In the dreaming of the Indigenous people, the Coalsack formed the head of the Emu and if you follow the dark dust lanes of the Milky Way east towards the Scorpion, you will see the Emu’s body and legs. There are lots of stories about Crux and the Pointers. Some say that Crux is the Eagle’s foot and the Pointers are the throwing stick used to hunt with. Others see the Milky Way as a river with Crux as a fish or stingray and the Pointers as two white cockatoos sitting in a tree.
Centaurus is a mythical half-man, half-horse and in Greek mythology represented the scholarly centaur Chiron, who tutored many of the Greek gods and heroes. He was put among the stars after he was accidentally struck by a poisoned arrow fired by Hercules.
The brightest star in Centaurus is Alpha Centauri which is one of the Pointers. It is the Pointer which is more distant from the Southern Cross or the brighter of the two stars.
In telescopes, Alpha Centauri appears as two stars, and both these stars orbit around each other once every 80 years and are starting to move closer together; by 2037-2038 only medium aperture telescopes will be able to distinguish the two stars. There is also a third member of this group called Proxima Centauri and it is the closest star to us after our own Sun at about 4.2 light years away or 42 million million kilometres. It takes Proxima about one million years to orbit its two companions and it is a red dwarf star, making it a challenge to see – it is not even in the same field of view as its companions.
So what else can we look forward to seeing in the sky in May 2015?
After sunset in the northern sky is Jupiter. It is easy to find as it is the brightest object in that area of the sky, located in the constellation Cancer. Binoculars will show you the four largest moons known as the Galilean satellites and small aperture telescopes will show one or two of the Jovian clouds belts. On the 24th, the 6-day old waxing crescent Moon appears above and slightly to the west of the gas giant.
Mercury is low in the northwestern sky this month. It is at its greatest elongation, 21 degrees east of the Sun on the 7th and, at this time, will only be 6 degrees above the horizon, making it difficult to see in the twilight glow. By mid-month Mercury will disappear from our evening skies.
Low in the eastern sky after sunset in the constellation Scorpius is the wonderful ringed-planet, Saturn. On the 4th, Saturn will have its closest approach to the bright star Beta Scorpii. Saturn’s impressive ring system can be seen in even small aperture telescopes and depending on the telescope you are using you may even catch a glimpse of a few of Saturn’s moons including the second largest in our solar system, Titan. In the middle of the month Saturn moves into the constellation Libra. On the 5th, the just past Full Moon will be slightly above and to the east of the ringed planet.
Venus shines brightly in the early western sky after sunset. Early this month it moves out of Taurus into Gemini where it will remain for the rest of the month. On the 21st, the 3-day old waxing crescent Moon is slightly above and to the west of the dazzling planet and on the 22nd, the 4-day old waxing crescent Moon is directly above Venus.
Saturn is in the western sky this month for all you early-birds! On the 6th, the waning gibbous Moon is above and to the north of the planet.
I don’t have one wildcard for you all this month. Usually the Eta-Aquarids meteor shower is worth a look however this year the peak is on the 6th and with a bright gibbous Moon in the sky, even from a dark location it will be difficult to see all but the very brightest meteors.
I leave you now with a quote from Jill Tarter, astronomer and former Director of the Centre for SETI Research: “We, all of us, are what happens when a primordial mixture of hydrogen and helium evolves for so long that it begins to ask where it came from.”
Wishing you clear skies and see you next month under the stars!
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’ for 2015. It not only contains detailed monthly sky guides, but is 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 (additional costs apply).
This has been Melissa Hulbert from Sydney Observatory with the May sky guide.