To help you learn about the southern night sky, Sydney Observatory provides a guide and a sky map or chart each month. This month’s guide is presented by Melissa Hulbert, Sydney Observatory’s Astronomy Programs Coordinator.
In the May sky guide, as well as showing us where to find the constellations Orion, Scorpius, Centaurus and Crux, and the star clusters, the Jewel Box, M6 and M7, Melissa tells us the best times to see the planets Jupiter, Mars and Saturn and the best time to see the Eta-Aquarid meteor shower.
SEE THE SKY CHART
We provide a May 2016 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.
READ THE GUIDE
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 chart.
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 2016?
After sunset in the northeastern evening sky is Jupiter. It is easy to find as it is the brightest object in that area of the sky. It is in the constellation Leo. 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 15th the 9-day old waxing crescent Moon appears just above and very close to the gas giant.
Low in the south-eastern sky is the red planet, Mars. It starts the month in the constellation Scorpius before moving into Libra by the end of the month. May and June are ideal months for observing mars this year. On the 22nd Mars reaches opposition (when a planet or other celestial object is opposite the Sun in the sky as seen from Earth) and has a closest approach to us on the 31st at a distance of 75, 279, 145 kilometres. On the 22nd the Full Moon will be directly below the red planet and on the 21st, to the left or east of Mars.
Low in the southeastern sky in the second half of the month sees the wonderful ringed-planet Saturn rising in the constellation Ophiuchus. 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. On the 22nd, the full Moon will be above and to the left (east) of Saturn and on the 23rd the Moon will be directly below the ringed-planet.
During May, Mercury is lost in the Sun’s glare and will transit the Sun on the 10th. Unfortunately this transit is not visible in Australia – we have to wait until 2032!
Venus also remains lost in the Sun’s glare this month and will return to the evening sky in mid-July.
I do have one wildcard for you all this month which is the Eta-Aquarid meteor shower. This shower is linked to Halley’s Comet and is one of the most popular in the southern hemisphere. When comets pass by us and pass close to the Sun they leave a trail of small particles and dust behind. When the Earth passes through this trail we see lots of meteors appearing to come from the one area of the sky. This is called the radiant and each shower is named after the constellation or bright star near which the radiant appears. In this case it’s the constellation of Aquarius and the star is Eta Aquarii. The shower runs between the 19th April and the 28th May, with the peak on the morning of 5th May.
At its peak the rate will often be around 55 per hour. The Eta Aquarids are usually very swift and are a striking yellow colour. They are also known for their trains with about 25% of meteors leaving a train behind.
The best time to observe any meteor shower is after midnight, usually a few hours before dawn, so on the morning of the 5th, look towards the east. There will be no Moon in the early hours of the morning, as its New Moon so perfect conditions for viewing.
The Eta-Aquarids have a history of good performance. In 1975 there was an hourly rate of 95 and in 1980, an hourly rate of 110!
I leave you now with a quote from Henry Wadsworth Longfellow, Evangeline: A Tale of Acadie:
“Silently, one by one, in the infinite meadows of heaven,
Blossomed the lovely stars, the forget-me-nots of the angels.”
Wishing you clear skies and see you next month under the stars!
This has been Melissa Hulbert from Sydney Observatory with the May sky guide.