August 2007 night sky guide and podcast

To help you learn about the southern night sky, Sydney Observatory provides a night sky star map or chart for each month of the year (see the link below). We also provide an audio guide of the month’s night sky, presented by one of Sydney Observatory astronomy experts (this link also below). You can listen online, or download the audio onto your ipod or mp3 player.

Dr Nick Lomb, Sydney Observatory curator of astronomy, guides us through the highlights of the southern night sky which, for the month of August, include the constellations: Scorpius, Sagittarius, Lyra and Crux (the Southern Cross); and the planet Jupiter (including, with a small telescope, its four Galilean moons).

Nick also provides information about the total eclipse of the Moon (when the Moon moves into the Earth’s shadow) on the evening of Tuesday 28 August.

One of Nick’s helpful tips this month is that if you are planning to use our sky chart, below, or the more detailed information and chart in the book, ‘Australian night sky guide’, then, it’s a good idea to cover your torch with red cellophane, as white light adversely affects your adaptation to the dark.

For more about what you’ll see in the southern sky in August, listen to the podcast or read the transcript.

The night sky map shows the stars, constellations and planets visible in the night sky from Sydney, Australia, and will also be usable at any other place in Australia. Special directions are given to help you locate the Southern Cross, also called Crux, for any time of the year. The locations of two nearby galaxies, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), are also given. Each month’s chart is placed online at the end of the previous month.

The monthly star maps are provided as PDF or portable document format files. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.

pdf August 2007 night sky guide map

Read the transcript.

 

 August 2007 night sky podcast: Play Now | Play in Popup | Download

Harry sketches the last Herschel crater

Crater Herschel, drawn by Harry Roberts

Sometimes, even in the city, astronomical seeing can be excellent. July 23 provided such an evening when the 4.8 mm Nagler [high quality, wide-field telescope eyepiece] gave the best views at over 400 magnification, a rare occurrence. Knowing it wouldn’t last I chose smallish crater Herschel for a drawing, so completing a portrait of each of the three craters bearing the Herschel name.

Herschel is a fresh formation in the intensively cratered highlands close to the centre of the lunar disc, and it’s sited on the north rim of giant crater Ptolemaeus. Herschel looked a lot like Aristarchus, a fresh, round and deep crater. The morning terminator lay 11º west of the site and shadow filled the crater floor to the base of the central chain of peaks. And, like Aristarchus, Herschel seemed to have radial banding on its inner slopes.

The central peaks form a long chain from the centre to the foot of the northern wall. They are highest near the centre however, where they cast shadows across the floor. The inner walls showed a variety of collapse landforms. The wall between secondary craters G and X had a bright main scarp up to 4km wide above a dimly lit terrace. Below the terrace several concentric slump blocks could be seen. East (right) of the central chain the crater was in shadow except for a part of the inner wall near G where a curved fan of slippage debris spilled across the floor. On the west (left) side of the central chain two irregular patches of dark melt could be seen on the floor.

The main scarp on the east (right) rim of the crater contrasts with the west side. Several concentric terraces could be seen very close to the rim. The main scarp there must be shallow, and perhaps steeper slopes.exist on the east side.

NE of Herschel is an extraordinary landform labelled E in Rükl’s “Atlas”. I have sketched this landform in outline only, as it was immensely complex. It’s a dramatic example of the enormous linear divots (“linearments” Wood p 141) that occur in this part of the Moon. They are all radial to Mare Imbrium, and are clearly caused by high velocity ejecta from that impact event. Secondary crater N has been partly cut in half by linearment E. Other linear features occur between E and Herschel that I have omitted for clarity; the whole area has been raked by debris. Crater Herschel itself shows none of the linear “raking” and obviously post-dates the Imbrium event. Note the linear ridges at the centre of linearment E that are common in oblique impact formations. Crater Spörer just N of Herschel has been raked over by the Imbrium debris too.

Herschel is 41 km wide and almost 4 km deep, and dates from the Eratosthenian Era from 3.7 billion to 1.1 billion years ago. I guess it’s younger rather than older. It’s named of course after William Herschel 1738 – 1822, who can claim to be the first astronomer of the modern era, discovering Uranus and describing and mapping 2500 deep sky objects.

Enjoy the Moon.

Harry Roberts
[Expert lunar observer & member of the Sydney City Skywatchers - Nick]

How Captain Cook found his longitude

K1 chronometer, courtesy National Maritime Museum UK

Yesterday afternoon (Tuesday 24 July 2007) Sydney Observatory staff farewelled the Director of the Director of the Powerhouse Museum, Dr Kevin Fewster. Dr Fewster has been appointed the Director of the National Maritime Museum at Greenwich UK that includes the Royal Observatory, Greenwich, the centre of time and space on Earth.

Naturally, the talk turned to time measurement and the wonderful Harrison clocks on show at Greenwich. Dava Sobel has ably told the story of the clocks and their maker John Harrison in the best-selling book Longitude.

Interestingly Captain James Cook on his first voyage did not have a chronometer on board his ship the Endeavour. H4 was still the only one then in existence and that was far too precious to send on a highly risky voyage. So how did Cook find the longitude, that is how far he was east or west of Greenwich? He used the method of lunar distances. In one of the great coincidences in the history of science two techniques of determining longitude at sea were developed at the same time, lunar distances and chronometers.

Lunar distances involve measuring the angular distances of stars from the Moon. More precisely three observations are made, of a star’s elevation above the horizon, of the Moon’s elevation of the horizon and of the angular separation between the star and the Moon. This is then repeated with another star. The measurements of angular distance are made with a sextant, an instrument based on the previously invented octant, but modified to be able to measure larger angles for use with lunar distances.

Sextant, image Nick Lomb

After taking the observations Cook had to do long and laborious calculations to establish the ship’s position. To assist he used the Nautical Almanac published at Greenwich. Unfortunately, at the start of the three year voyage in 1768 only the almanacs for 1768 and 1769 were available so they were the only ones he could take on the voyage.

For his subsequent voyages Cook did take chronometers. Kenneth Slessor has a wonderful poem, Five Visions of Captain Cook. The short extract below refers to two chronometers including K1, Larcum Kendall’s famous replica of H4, which is pictured at the top of this post:

Two chronometers the captain had,
One by Arnold that ran like mad,
One by Kendal in a walnut case,
Poor devoted creature with a hangdog face.
Arnold always hurried with a crazed click-click
Dancing over Greenwich like a lunatic,
Kendal panted faithfully his watch-dog beat,
Climbing out of Yesterday with sticky little feet.

Bird Watching and the Stars

Five constellations drawn by Alan Plummer

The greenshank, a small bird with a long beak and olive green legs, breeds in Scotland and occasionally visits Australia. You now know this gem because amateur birdwatchers all over the world have lodged their observations for decades with various agencies for all to use. Why should the professional do a job that others do for free? The ornithologist is left to do the more rigorous observing and other science, using data gathered by amateurs. Aspects of astronomy are the same.

The astronomical equivalent of the ‘twitcher’ is the variable star observer. (That is, observing stars that change in brightness over time.) But staying with birds for a minute more, here are the avian constellations:

Cygnus the swan
Aquila the eagle
Corvus the crow
Tucana the toucan
Grus the crane
Pavo the peacock
Columba the dove
Phoenix the firebird
Apus the bird of paradise

And to be complete, we can include the now unused (extinct?) constellation of Gallus the cockerel, which is now a part of Puppis.

There are thousands of under-observed variables in the sky, and here are three examples that can be observed from light polluted skies. You’ll need an atlas, charts, a small telescope or medium size binoculars. And some instruction; but as with any volunteer work, all you have to do is ask.

Theta Apodis, charted above, in Apus. This star makes the far southern point of a stretched triangle with Alpha and Beta Centauri. It varies from magnitude 5 to 7 over 119 or so days. You’ll need binoculars or a telescope with 60mm of aperture or more for this star, and observe it once a fortnight. If you do this methodically, you’ll possibly be the only observer in Australia doing it.

S Apodis, also charted above. You’ll need 100mm of aperture or more here. Unlike Theta Aps, this star is well observed. For a good reason: it pulsates from 10.9 to 9.9 magnitudes somewhat regularly, but can disappear suddenly and unpredictably behind a veil of carbon soot. It is an ‘R Coronae Borealis’ type variable star, and should be observed on every clear night. Professional astronomers depend on amateurs for notification of fading events. The light curve from the American Association of Variable Star Observers over the last ten years is shown below.

The light curve of the variable star S Apodis, courtesy of the AAVSO

Y Pavonis, in Pavo. This will take some finding from city skies, but it will be worth it. Y Pav is a carbon star, so its reddish color will be striking. With a visual range of 5.6 to 7.3 magnitudes over 233 days, you’ll need 60mm or more of aperture, and observe it once a month. As with Theta Aps, you’ll probably be the only one in Australia.

Note that the above visual ranges and periods are apt to change according to the ongoing evolution of the star; that’s why they should be kept under observation. Anyone wanting to get involved in this valuable – and entertaining – pastime can go to aavso.com.org and click on the ‘for new observers’ tag. And after a bit of practice you can enjoy the sky as more than just a sight-seer.

Alan Plummer. Linden Observatory

Saturn now has 60 moons

Saturn’s new satellite, S/2007 S4, courtesy NASA/JPL/Space Science Institute

An instrument scientist, Carl Murray, looking at images taken by the Cassini spacecraft on 30 May this year spotted a new moon circling the planet Saturn. He and his colleagues verified the discovery by looking back through previous images of Saturn’s rings from Cassini and finding it recorded on images back to June 2004. Scientists estimate that the new moon is tiny with a width of only about 2 km.

It is likely to take some years for the new moon to be given a permanent name by the International Astronomical Union. In mean time it has a formal designation of S/2007 S4 and informal name of Frank among the Cassini scientists.

In recent years the number of known moons of Saturn and that of the other giant planets in the solar system has increased considerably mainly due to the work of scientists from the University of Hawaii. In fact, the Hawaiian astronomers announced the discovery of 12 new moons around Saturn at the beginning of May 2007. They had first observed these moons in 2004.

The known moons of Saturn since 1993 taken from the Sydney Observatory/Australian Sky Guide, graph by Nick Lomb

With 13 new moons to be named has anyone any suggestions for the IAU?

The 2007 Australian Sky Guide to the rescue, again

Those of us with the 2007 Australian Sky Guide by Dr Nick Lomb would have known that one of the highlights for July was last nights gathering of objects in the Eastern sky shortly after sunset.

Venus, the Moon with easily visible Earthshine and Saturn made for a wonderful photo opportunity.

If you managed to get a nice photo please send it to me at geoffw@phm.gov.au and I’ll put it up my attempts.

To make sure you don’t miss out on any other spectacular views like this you can obtain your 2007 Australian Sky guide from most large bookstores or visit our monthly astronomy page under the blog at www.sydneyobservatory.com

Enjoy.

What was there before the Big Bang? – a new theory from Roger Penrose

Sir Roger Penrose, from the 7th Edoardo Amaldi Conference on Gravitational Waves

On Friday evening, 13 July 2007, the British physicist, Sir Roger Penrose, gave a mind-expanding and mind-boggling talk at the Darling Harbour Convention Centre. The public lecture was part of the 7th Edoardo Amaldi Conference on Gravitational Waves and it involved the presentation of the Dirac Medal of the University of NSW to Sir Roger.

Until now the official answer to the question of what was there before the Big Bang was that we do not know and we will never know as time only began at the Big Bang. About two years ago Sir Roger thinks he may have found an answer that he presented to a fascinated audience in the Bayside Auditorium. Your humble blogger attended the lecture and attempts a brief summary below:

He started by stressing the importance of the second law of thermodynamics that states that disorder or entropy must always increase. For example, at the Big Bang the Universe began in a low entropy state as illustrated by studies of background radiation left over from shortly after that time, the cosmic microwave background. Since then entropy has always increased.

Sir Roger also mentioned the Weyl curvature. This is a property of space that leads to the bending of light rays from distant galaxies by ones in the foreground – usually referred to as gravitational lensing. His Weyl curvature hypothesis proposes that the Weyl curvature was zero at the big bang.

According to the new theory as the Universe expands all the particles of matter are collected into black holes. These destroy the information content of matter and hence reduce entropy. The black holes radiate Hawkins radiation and after a very very very long time disappear – for instance for a three million solar mass black hole like the one at the centre of the Milky Way the time is 10 to the power of 84 years. When all matter has disappeared and entropy has been reduced a new Big Bang can take place. Sir Roger calls this sequence of one universe being formed after the death of the previous one conformal cyclic cosmology.

There are observational consequences of the theory as the previous Universe may have left behind a faint subtle pattern in the cosmic microwave background. It is now up to observational cosmologists to search for that tell-tale pattern.

SUSI observes a candidate supernova – Gamma 2 Velorum

The Sydney University Stellar Interferometer, courtesy the University of Sydney

Astronomers using the Sydney University Stellar Interferometer at Narrabri in NSW have recently observed the fascinating double star Gamma 2 Velorum, that was briefly mentioned recently on this blog. This system consists of a hot and massive star being circled by another hot star that is at a very late stage of its lifecycle and hence is a candidate to explode as a supernova.

The two stars are so closely together that they cannot be seen separately by an optical telescope, not even by the sharp vision of the Hubble Space Telescope. However, the system can be separated with SUSI which uses the interference of light to resolve extremely tiny angles in the sky.

The team of astronomers led by Julian North obtained full details of the system including the masses of the two stars, their brightnesses and the separation between them. They found that the double star is at a distance of 1095 light years from us. Other teams using different techniques have generally found a closer distance. Interestingly, the distance obtained in 1970 from a previous Sydney University instrument, the legendary Narrabri Intensity Interferometer, was comparable though with much larger errors.

This work is a great example of what can be done with the help of an interferometer. Well done SUSI, Julian and the others in the team!

Active sunspot decays

Prominence on north-east edge of the Sun on Friday 6 July 2007, imaged by Monty Leventhal

A prominence is hydrogen gas held above the Sun’s visible surface by magnetic fields. This bright prominence was imaged by solar observer and member of the Sydney City Skywatchers, Monty Leventhal last Friday morning.

This and other prominences late last week announced the arrival of a large and active sunspot on the Sun. This sunspot is numbered 963. Such an active sunspot at this stage of the eleven year solar cycle where we are near the minimum of solar activity is a surprise. However, as over the last week the spot has moved towards the centre of the Sun’s disc it has faded in activity.

Monty provides the following information about the image:

Digital filtergram
Date:- 5-7-07 UT
Time:- 22.25 UT
Conditions:- (4) Poor
Supported by the Donovan Astronomical Trust, Sydney. Australia.
Camera:- Canon 300D
Filter:- DayStar T-Scanner. 6Å.
Telescope:- Meade S.C. 10 inch

Kip Thorne speaks on gravity waves

The Australian International Gravitational Observatory (AIGO) at Gingin, Western Australia

Famous American physicist and gravity expert Professor Kip Thorne gave a masterful exposition on black holes and gravity waves at Darling Harbour on the evening of Tuesday 10 July 2007.

Ripples in space time or gravity waves are predicted by Albert Einstein’s General Theory of Relativity. They occur when there are major events in the Universe involving massive bodies such as the merger of two black holes. Though we cannot observe such events visually theoreticians are studying them using numerical simulations. Other researchers are trying to observe gravity waves themselves.

There are a number of observatories in the US and in Europe looking for the tiny warping of space time with detectors that can detect the slightest movement of two mirrors four km apart. Australia has a small gravitational wave observatory at Gingin, WA that is pictured above, but it still needs to be expanded to full size. The Australian AIGO is an important link in the chain of such observatories as without it any detected gravitational wave could not be localised in the sky and hence identified optically.

The existing detectors can already pick up movement that is 1000th of the width of an atomic nucleus. Upgrades at the end of this decade will improve the sensitivity by a factor of 10, a sensitivity at which quantum mechanical effects become important.

Gravity waves have not yet been detected, but Kip Thorne indicated that he is confident that that will occur in a decade or two. Once we are detecting them, scientists hope to use gravity waves to study for the first time not only black holes, but the instant of the big bang itself 13.7 billion years ago.