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 Melissa Hulbert, an Astronomy Educator at Sydney Observatory.
Mel points out constellations to look out for this month (Orion the Hunter, Scorpius the Scorpion, and Crux or the Southern Cross), planets (Venus, Saturn, Mars and Mercury) and tells us about the Eta Aquarid Meteor Shower which should be visible until 27 May, with the peak on 5 May.
Mel also gives a preview of the rare astronomical event on 6 June this year – the transit of Venus. The following one won’t be until 2117! You can buy the book, ‘Transit of Venus: 1631 to the present’, by Dr Nick Lomb, which is beautifully designed and full of fascinating information about this historically important astronomical event. Also, keep posted for news about our iPad version of the book which will be available in the iTunes store soon. We’ll let you know when it’s available and we also provide more information about the transit of Venus on our web pages.
All this and more in the audio and transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a May 2012 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 2012 Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2011 until December 2012 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 May 2012 monthly sky guide audio
Hello and welcome to the night sky guide for May. My name is Melissa Hulbert and I’m an Astronomy Educator 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 on the Astronomy tab and look for ‘monthly sky guides’.
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 – that’s 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 that 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 catalog names. M stands for Messier and is named after Charles Messier, an 18th century French comet chaser. He made a catalog 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 catalog 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 represents 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 2012?
This month just after sunset look towards the north-west. Venus spends the month in the western twilight sky before becoming lost in the Sun’s glare as it moves towards inferior conjunction (when an inferior planet, Mercury or Venus, passes between the Earth and the Sun) and towards a rare Transit if Venus next month on the 6th June. Remember that you cannot look directly at the Sun. You need to use a telescope with a special filter over it or a pair of eclipse glasses to safely view the transit. More details about this can be found on our website, in the ‘2012 Australasian Sky Guide’ and in upcoming podcasts. If you miss it this time, you will have to wait until 2117.
Mars is high in the northern sky in the constellation of Leo during May. The first half of the month will be the best time for viewing as its magnitude starts to drop making it at its faintest since the beginning of the year. Mars will have close encounters with the Moon twice this month. The 9-day old Moon will form a triangle with Mars and the brightest star in Leo, Regulus, on the 1st. The 8-day old Moon will be above Mars on the 29th.
Saturn is still gracing our skies and is rising in the eastern twilight sky in the constellation Virgo. The Full Moon will be above Saturn on the 4th along with the bright star Spica. If observing Saturn through a telescope be careful of the star HD 118129 which will be in the field of view between the 4th and the 6th and could be mistaken for the planet’s largest moon Titan. On these nights, Titan will be closer to the planet.
May is again not one of the best months for all you early-birds! Though if you love early mornings then Mercury will be low in the eastern pre-twilight sky. However make sure you catch it early in the month as it will start to move closer to the Sun and by the 27th it is at superior conjunction (this is when Earth and Mercury are on opposite sides of the Sun).
I do have one wildcard for all you daredevils 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 18th April and the 27th May, with the peak on 5th May. But the rate of meteors per hour is generally above 30 from about the 3rd-10th of this month. At its peak, the rate will often be around 70 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 these meteors leaving a train behind. The best time to observe any meteor shower is after midnight, usually a few hours before dawn.
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! There will be a Full Moon during the early hours of the 5th May which is not ideal as the light from the Moon will interfere with observations of fainter meteors. Best observing conditions for this event will be away from the city lights.
There is still time to purchase a copy of Nick Lomb’s book on the Transit of Venus. It has been meticulously researched and is full of lavish photographs. A real must if you’re interested in this rare astronomical event.
It is available from Sydney Observatory and Powerhouse Museum shops or you can purchase it online through Powerhouse Publishing.
You can also subscribe for free to our Sydney Observatory monthly sky guide podcasts through iTunes.
I leave you now with a quote from Galileo Galilei “I’ve loved the stars too fondly to be fearful of the night.”
Wishing you clear skies and see you next month under the stars!
This has been Melissa Hulbert from Sydney Observatory with the May monthly sky guide podcast.