Observations

November 2012 night sky guide podcast, transcript and sky chart

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, Sydney Observatory Astronomy Educator.

In the November sky guide, as well as showing us where to find the constellations Pegasus, Orion and Taurus, and the star clusters, Hyades and Pleiades, Mel tells us to look out for the close view of Mars and the crescent Moon on 16 November. For this and more, listen to the November 2012 night sky guide audio, or read the transcript below.

HEAR THE AUDIO
You can subscribe with iTunes or upload the (21 mins 10 secs) audio to your iPod or mp3 player, or listen to it on your computer.

SEE THE SKY CHART
We provide an embedded sky map (below) and a November 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.

November 2012 night sky chart

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). The 2013 edition is expected to be available from November 2012.

READ THE TRANSCRIPT (after the jump)

Transcript of the November 2012 monthly sky guide audio

Hello and welcome to the night sky for November. 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 November sky map from our website at www.sydneyobservatory.com.au. It can be found under the Astronomy tab.

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.

Look towards the north. High in the northern sky is Pegasus, the winged horse from mythology, probably with its origins in both Mesopotamian and Etruscan starlore. Pegasus was said to have been born from the blood of Medusa (the Gorgon) after she was slain by Perseus from Greek mythology.

He is also associated with poetic inspiration in Greek mythology with a fountain that was sacred to the Nine Muses which was created when he stamped his hoof on Mount Helicon. Pegasus was principally the steed of Bellerophon and in a dream Athene appeared to Bellerophon with a golden bridle and advised him to ride Pegasus. However some legends say that Perseus rode the winged horse when rescuing Andromeda.

Pegasus is easy to find, with the best-known feature of this constellation the aptly named ‘Great Square of Pegasus’. It is rather large at over 15 degrees in width and 13 degrees in height, but despite its size there are relatively few bright naked-eye stars within the Square. 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. This does work for everyone, as your arm length is proportional to your hand size.

Four stars outline the Square and in the past all four were a part of the constellation, however delta Pegasi is now known as Alpha Andromedae. This star was also known as Sirrah meaning ‘navel’ and marked the navel of the horse. Pegasus is the right way up for us, so we see the neck and head of the horse stretching towards the west and what appears to be his back legs towards the north-east. One interesting object is M15 or NGC 7078, a magnitude 6 globular cluster, easily visible in binoculars and small telescopes. Medium to large apertures will resolve some of the outer regions of this cluster and a dense core. M15 lies about 33,000 light years away.

Remember I mentioned the horse’s rear legs earlier? Let’s go back to those. The legs are part of the constellation Andromeda, the daughter of Queen Cassiopeia in Greek mythology. If you are away from city lights then look carefully at this area of the sky. You might see an elongated fuzzy patch of light with your unaided eye. This is the Andromeda Galaxy and is the most distant object visible to the unaided eye, lying about 2.4 million light years from us, though recent data from the Hipparcos satellite has suggested that this distance might be closer to three million light years. While a fascinating sight with just your eyes, if you have binoculars or a small telescope then a most amazing sight awaits you – the dark dust lanes of the spiral arms, a bright core, and if you are lucky you might pick up one or both of its companion galaxies.

To the east and slightly south of Pegasus is Cetus, the fourth largest constellation in the sky. Cetus has been depicted as a variety of animals but is generally depicted as a sea-monster or dragon-fish but some refer to it as merely a great whale.

Cetus is one of the most ancient constellations in the sky as it was Ptolemy who originally assigned 22 stars to this constellation. It contains a jewel box of coloured stars for both telescope and binocular users alike.

South of Cetus you will see the brilliant star Achernar, which means ‘the river’s end’ as it marks the end of the river, Eridanus.

Follow Eridanus towards the east and there rising in the sky is our familiar signpost of summer skies – 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 on his side as he rises above the eastern horizon.

The middle point of light in the handle of the Saucepan (or the sword) is the famous Orion Nebula or M42. It is one of late spring’s most magnificent sights and will keep observers using binoculars or a telescope enthralled as you follow the swirls and loops of gas and dust in this active stellar nursery. Stars are forming out of the gas in this nebula which stretches about 20 light years in diameter and is 1,500 light years away.

To the south of ‘the Saucepan’ you should see the red supergiant star Betelgeuse, which is 500 times larger than our own star, the Sun. Or, if we were to place Betelgeuse where our Sun is, at the centre of our Solar System, then the edge of the star would be near Jupiter’s orbit. Betelgeuse is the shoulder or armpit of Orion and is about 427 light years away. To the north of ‘the Saucepan’ and diagonally opposite Betelgeuse is a brilliant white star, Rigel, one of Orion’s knees. Rigel is a blue-white supergiant star that shines 60,000 times brighter than our own Sun. Rigel also has a small companion star which is best seen through a telescope though if seeing conditions are not the best, small telescopes will struggle to see the companion through the glare of Rigel.

Let’s return to the belt of Orion and follow its line to the west where we come to the back of a sideways ‘V’. This ‘V’ is the head of Taurus the bull and appears to be charging at Orion. Like Cetus, Taurus is one of the most ancient constellations in our skies and like Orion is also steeped in Greek mythology. It is said to represent the bull Zeus changed into to carry Princess Europa off to Crete.

Back to the ‘V’ which is part of a large open star cluster visible in binoculars called the Hyades. One of Taurus’ eyes is an orange giant star called Aldebaran which means ‘the follower’. It follows the Pleiades, a wonderful open star cluster that can be seen with your eyes to the north west of the ’V’. The Pleiades are known as the seven sisters as seven stars are readily seen with your eyes, but away from city lights, up to 13 can be seen with the unaided eye. The whole cluster contains about 100 stars and binoculars are the best way to view this marvelous object.

Another of Messier’s objects, M1 is also in Taurus. M1 is best seen in telescopes and is known as the Crab Nebula, but is in fact the remnant of a star that exploded as a supernova on July 4 1054AD. How can we be so precise with this date?

Chinese astronomers kept very accurate records of the night sky and recorded the position of a ‘new star’ on their star maps on this date, the exact position in which we now find the Crab Nebula. Although the Crab Nebula is 7,000 light years away, the supernova was brighter than the planet Venus for weeks before it faded from view after almost two years. Even today, the nebula is still expanding at a rate of more than five million kilometres per hour. It emits radiation in all wavelengths from gamma rays to x-rays, UV, optical and infrared radiation and radio waves. It is exceptionally bright for a supernova remnant. The reason for this is its central pulsar energizes it.

Careful studies of the Crab Nebula revealed a pulsar near the centre, which emitted at a rate of 30 pulses per second. Additional observations have shown that the pulse rate is slowing down. During the next 1,000 years the pulse rate will fall to half its present value.

Time to turn and look towards the south. Can you see our familiar signpost of the Southern Cross and Pointers? Look low, close to the south horizon and there they are. In late spring these constellations are low in our evening skies but by early morning, they are rising again to the positions we are familiar with.

However, in their place are two cloud-like objects, a large one and a small one (you will need to be away from city lights to see them). These are the Magellanic Clouds, named after the explorer Ferdinand Magellan. They are the two satellite galaxies of our own Milky Way. The larger of the two is in the constellation Dorado, the goldfish. In 1987, the Large Magellanic Cloud (LMC) was the site of the first supernova, visible to the unaided eye since 1604 (which was observed by the astronomer Johannes Kepler). This supernova was named Supernova 1987A.

The Small Magellanic Cloud (SMC) is in the constellation Tucana the Toucan. Sitting just beside the cloud is 47 Tuc or NGC 104 a fine globular cluster, second only to Omega Centauri. It is a fuzzy object which at 4th magnitude can be easily seen with the unaided eye, away from city lights. In ancient times it was thought to be a star and given a stellar designation. 47 Tuc has the same apparent size as the Moon and has a tightly packed core. Telescopes with apertures of 100mm or greater are required to even begin to resolve this globular. It is 16,000 light years away, making it one of the closest globulars to Earth.

So what else can we look forward to seeing in the sky in November 2012? This month after sunset, look towards the west and there are Mercury and Mars. Mercury will only be visible for the first half of the month before we lose it to the glare of the Sun.

Mars spends the entire month in the western evening sky, setting around 10:30pm Australian Eastern Daylight Savings Time (AEDST). On the 18th Mars crosses the outer regions of M8, the Lagoon Nebula and on the 24th and 28th it passes M28 and M22 respectively. Both M28 and M22 are globular clusters. A globular cluster typically consists of older stars in a large, compact, spherically shaped cluster and is found in the outer regions of galaxies.

On the 16th, the 3-day old crescent Moon is just below and to the right of Mars.

In the early evening in the east, a brilliant star-like object shines. This is the planet Jupiter, the largest planet in our Solar System. On the 1st and 2nd, the waning gibbous Moon is close to the planet. On the 28th and 29th the Moon again joins Jupiter in sky. On the 28th the nearly Full Moon is above Jupiter and on the 29th the Full Moon is below Jupiter.

November also has something in store for all of you early-birds! Venus is a brilliant-star like object in the pre-dawn sky and on the 12th, a 27-day old waning crescent Moon forms a triangle with Venus and the bright star Spica. While Venus starts to move towards the Sun, Saturn returns to the eastern pre-dawn sky and on the 27th, both planets are very close together in the sky – only 0.6 degrees apart! Saturn will be below Venus on the 27th and on the 28th one degree to the right of Venus.

I do have one wildcard for all you daredevils this month which is the Leonids meteor shower. This shower is linked to the periodic comet 55P/Tempel-Tuttle and is usually at its best about every 33 years when the comet returns. When comets 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 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 Leo and the radiant is within the sickle or head of the lion. The best time to observe any meteor shower is after midnight, usually a few hours before dawn. The Leonids are active from the 8th to the 27th of November, with the peak on the morning of the 17th. Activity can vary from year to year and if the shower does turn out to be active this year it is certainly worth hopping out of bed for!

I’ve saved the best event for observers for last! A solar eclipse will occur across Australia on the 14th. A solar eclipse is when the Moon passes directly between the 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, 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 five. Thus, solar eclipses occur two to five times a year, with one particular locality seeing a total eclipse about once every 350 years.

The Moon’s shadow sweeps across Earth at speeds of about 1700Km/h, due to a combination of the Earth’s rotation and the Moon’s orbital motion, thus a solar eclipse occurs over a short period of time.

On the 14th November 2012 the total solar eclipse will be only visible along the narrow track that’s just 179 kilometres across at its widest point. This track crosses just north of Cairns and observers in this city will see totality. Across the rest of Australia, a partial solar eclipse will 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 months eclipse starts early on the morning of the 14th, just after sunrise at 5:44am AEST. As the eclipse starts early a good view of the eastern horizon is essential. Totality, if you are under the narrow track, occurs at 6:39am and the whole event is over by 7:39am.

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 on your telescope or binoculars or 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. If you are under the narrow path that allows you to see totality then there is a small part of the eclipse that is safe to watch with just your eye-totality itself. Once totality occurs it is safe to look directly at the eclipse, without eye protection – but as totality will be short in this eclipse, about two minutes or less, observers must be extremely careful!.

A total solar eclipse is an awe-inspiring event to witness and something that should not be missed! However if you can’t make it to Cairns this year don’t despair! The next mainland total solar eclipse occurs on 22 July 2028 in Sydney.

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’. It not only contains detailed monthly sky guides, but is jam-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 subscribe to these podcasts through iTunes. Just search for Sydney Observatory monthly sky guides. If you search just ‘Sydney Observatory’, you’ll find not only our free monthly sky guides but also our self guided walking tour app that for $1.99 will guide you around Sydney Observatory grounds, Observatory Hill over looking our beautiful Sydney Harbour, on to the bridge and through the historic Sydney Rocks area.

Sydney Observatory is open for booked night visits, which includes a visit to the telescope domes and a telescope view of the night sky on clear nights. On cloudy nights we offer a mini planetarium session instead.

Sydney Observatory is also open most days from 10am-5pm. You can visit during the day without a booking. It’s free to look around the exhibition and the grounds. There are charges for staff-led daytime programs.

Information on all this and more is available at www.sydneyobservatory.com.au
Click on the ‘Astronomy’ tab at top right, then chose ‘monthly sky guides’ from the left side bar for the sky guides.

I leave you now with a quote from ‘The Eclipse of the Sun, 1820’ by William Wordsworth:
High on her speculative tower

Stood Science waiting for the hour

When Sol was destined to endure

That darkening of his radiant face

Which Superstition strove to chase,

Erewhile, with rites impure.

This has been Melissa Hulbert from Sydney Observatory with the November monthly sky guide podcast.

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