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, one of Sydney Observatory’s Astronomy Educators.
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.
May 2013 is pretty special with a meteor shower and a solar eclipse! The Eta Aquarids meteor shower takes place for most of May with the peak on the 6th. The solar eclipse will occur on 10th May this year. It will only be seen as a total eclipse along a narrow pathway across Australia but it will be visible as a partial eclipse from capital cities. Included in the transcript below is information about when the partial eclipse is visible from major cities around Australia. This fact sheet about the eclipse is produced by the Astronomical Society of Australia.
There’s a lot happening in our sky this month, so listen to the audio, or read the transcript below for more details.
SEE THE SKY CHART
We provide an embedded sky map (below) and a May 2013 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.
[scribd id=132579298 key=key-i6rioss9b9f2kjubdu9 mode=scroll]
BUY THE BOOK
Our annual book, ‘The 2013 Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December 2012 until December 2013 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 2013 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 under ‘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 2013?
Low in the west after sunset, Mercury will appear later in the month and has a few interesting encounters with Venus and Jupiter.
Venus returns to the evening twilight sky at the beginning of the month. In the latter third of the month, Venus will rise from below and pass Jupiter to the north, with Mercury close by the pair.
A conjunction of Venus with Jupiter and Mercury occurs on the 26th and 27th. Venus and Jupiter will be at their closest (one degree apart) on the 28th and 29th. On the 31st, Jupiter, Venus and Mercury will form a straight line in the evening twilight.
Mars remains lost in the Sun’s glare this month.
Jupiter is still in Taurus, now between the bull’s horns. As mentioned earlier, Jupiter has some wonderful encounters with Venus and Mercury later in the month however a slender 2-day crescent Moon will be between Jupiter and Aldebaran (brightest star in the constellation Taurus) on the 12th, another encounter not to miss.
Saturn is in the eastern evening sky after sunset and spends the first half of the month in the constellation Libra before moving into Virgo. On the 23rd, a 13-day old waxing gibbous Moon will be to the east of Saturn.
May is not one of the best months for all you early-birds, so enjoy a sleep-in this month!
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 6th May.
At its peak the rate will often be around 60 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 6th, look towards the east. There will be a thin waning crescent Moon on the morning but it should not interfere too much with 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’ve saved the best event for observers for last! An annular solar eclipse will occur across Australia on the 10th.
A solar eclipse is when the Moon passes directly between Earth and the Sun. A little quirk of nature means that the diameter of the Sun is 400 times greater than that of the Moon’s, but the Sun is on average 400 times farther away from the Earth, so both appear to have the same angular diameter (0.5) in the sky. It’s this combination that allows us to see solar eclipses.
When the Moon is directly between the Earth and the Sun, it casts a conical shadow on the Earth. The darkest part of the shadow is called the umbra and no part of the Sun can be observed at totality from Earth. The lighter part of the shadow is known as the penumbra and the Moon will only partially cover the Sun. What we see will depend on where we are in the Moon’s shadow.
Standing at the point on the Earth where the umbra falls, results in observers seeing the disk of the Moon completely covering the disk of the Sun. This is called a Total Solar Eclipse. Observers only slightly removed from the umbra shadow would be in the penumbral shadow and see only part of the Sun’s disk covered by the Moon. This is called a Partial Solar Eclipse.
If the Moon’s orbit was exactly in the plane of the Earth’s orbit, then we would see an eclipse of the Sun every month. However, this is not the case with the Moon’s orbit inclined by 5. Thus, solar eclipses occur two to five times a year, with one particular locality seeing a total eclipse about once every 350 years.
However this eclipse is an annular one, where the Sun forms a ring or annulus around the disc of the Moon. This occurs because the distance of the Moon from Earth varies due to the Moon’s elliptical orbit, which causes the apparent size of the Moon to change. When the Moon is close we get a total solar eclipse, like the one in November last year. However, this time as the Moon is near its furthest distance from the Earth, it appears smaller than the Sun and so the annulus or ‘ring of fire’ appears around the Moon. The umbra falls short of the Earth and so observers are in the part of the Moon’s shadow that extends beyond the umbra – the antumbra. If you are outside of the antumbra, in the penumbra, you will see a partial eclipse.
On the 10th May 2013 the annular eclipse will be only visible along the narrow track that’s between 171 and 225 kilometres across. This track crosses through Western Australia, the Northern Territory, and Far North Queensland before heading into the Pacific Ocean. [You can see the path across Australia of the total eclipse on Wikipedia.]
Across the rest of Australia, a partial solar eclipse can be seen. How much of the eclipse you will see, will depend on how close to the track you are – the closer you are, the larger the partial eclipse will be. This month’s eclipse starts early on the morning of the 10th, just after sunrise at 7:50am AEST (for Sydney and Melbourne). As the eclipse starts early a good view of the eastern horizon is essential.
[Here are the eclipse times for major cities in Australia:
Start – 7.09am; maximum – 8.15am; finish – 9.29am; % of Sun covered – 50%.
Start – 7.41am; maximum – 8.58am; finish – 10.28am; % of Sun covered – 52%.
Start – 6.58am; maximum – 8.07am; finish – 9.28am; % of Sun covered – 76%.
Start – 8.06am; maximum – 8.59am; finish – 9.57am; % of Sun covered – 23%.
Start – 7.50am; maximum – 8.52am; finish – 10.02am; % of Sun covered – 37%.
Start – 5.34am*; maximum – 6.36am*; finish – 7.45am; % of Sun covered – 79%.
*Sun is below the horizon. Sunrise for Perth is 6.55am.
Start – 7.50am; maximum – 8.57am; finish – 10.14am; % of Sun covered – 39%.]
I must emphasise CAUTION! It is dangerous to watch the eclipse while the Moon is moving across the Sun. You must use a special solar filter whether using a telescope or binoculars or even your eyes, need to be protected and for a few dollars you can purchase eclipse glasses which are just like a pair of sunglasses fitted with special film to protect your eyes. Even if you are under the narrow path that allows you to see the annular then there is a small part of Sun not covered by the Moon – the ‘ring of fire’ and you cannot look at this without proper solar filters and glasses, so observers must be extremely careful!.
For more on the night sky check our blogs in the ‘Astronomy’ section of the Sydney Observatory website www.sydneyobservatory.com.au There is also information there about our Facebook and Twitter accounts.
I leave you now with a quote from Edwin Powell Hubble (whom the Hubble Space Telescope is named after): “Equipped with his five senses, man explores the universe around him and calls the adventure Science.”
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 2013. 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).
You can also subscribe for free to our Sydney Observatory monthly sky guide podcasts through iTunes.
This has been Melissa Hulbert from Sydney Observatory with the May sky guide podcast.