Astronomical Society of Edinburgh
Journal 45

Scottish Astronomy Weekend 2002

On Friday 6th September the 14th Weekend of the Scottish Astronomers Group was opened by the SAG President, Mark Pollock who welcomed delegates to West Park Conference Centre, Dundee. A total of 62 delegates had travelled from all over the UK, from Inverness, Elgin, Aberdeen, Stirling, Falkirk, Edinburgh, Arran, Yorkshire, Fleetwood and the Isle of Man.

After his words of welcome, Mark outlined the weekend programme on the theme of Stars and then thanked the organisers Dr David Gavine, Brian Kelly and Dr Bill Samson for all their hard work organising the weekend.

Mark then introduced the first speaker; Dr David Gavine (ASE), who gave a talk, entitled Pioneers of Stellar Astronomy in which he traced the progress of stellar astronomy from the 18th century to the present day.

In the 18th century the stars were considered to be of little interest or importance because no-one knew what they were, other than being points of light. Telescopes only helped to show them as brighter points of light. The emphasis of astronomical interest therefore lay in mathematical calculations and the orbital mechanics of the planets. We learned how by the 19th century, William Herschel, considered by many to be the father of Stellar Astronomy, attempted to define the size and shape of the stellar system by counting and mapping stars in all directions.

In an attempt to measure the distance to the stars, astronomers tried to find the angle of parallax of a star. James Bradley's discovery of the aberration of starlight made astronomers aware of how very small and difficult to measure these angles would be. It was not until the late 19th century that Bessel and Henderson finally managed to measure the parallax to two different stars.

By the 20th century spectroscopy, photometers and CCD had revolutionised our knowledge of what stars are and how they work.

The meeting then adjourned to the hallway where we were given a civic reception by Deputy Lord Provost Charles Farquhar who welcomed the SAG meeting to Dundee and stressed how much importance Dundee Council placed on astronomy. This was to be encouraged especially in trying to make children more aware of the subject. Mark Pollock thanked Councillor Farquhar for his words of welcome and indicated that we were delighted to hear of the Dundee councillors support for astronomy and SAG hoped that this would ensure a secure future for the historic Mills Observatory.

The remainder of the evening was spent browsing around the bring and buy stall and looking at the images produced by the astrophotographers. There were displays of aurora observations and images of the aurora from as far afield as the USA. There was information about variable stars and examples of light curves, and Variable Star Section materials from the BAA.

To end the day, we sat in the garden outside the halls of residence talking, enjoying drinks and scanning the sky with binoculars. Several people went out in their cars to search for any signs of an aurora, as warnings had been issued by the NASA website earlier in the day. Sadly there was no aurora so they too joined us in the garden and a pleasant time was had by all. The barman has to have a mention as he kindly came out to the garden to refill our glasses. Now that's a civilised way to do casual observing!

 

On Saturday morning, the first lecture of the day was chaired by Brian Kelly, former City Astronomer, Dundee. He introduced Dr Bill Samson who spoke on the Evolution of the Stars.

Dr Samson began by describing the properties of stars. We heard that temperature is a function of mass. Stars of the same temperature may have different luminosities depending on their mass. Dr Samson then went on to describe how young stars begin to form from gravitational perturbations of the interstellar dust, eventually causing the formation of a dark globule. This falls inward and when the temperature reaches 107 Kelvin, hydrogen fusion begins. The life cycle of stars was then outlined:

Stars of less than 2 solar masses burn their fuel more slowly, at lower temperatures and become red giants eventually expelling mass to form a planetary nebula or become a white dwarf. Stars of more than 2 solar masses go through their fuel much more quickly and burn heavier and heavier elements until they reach iron which cannot fuse. Dr Samson described electron degeneracy pressure, where no two electrons can exist in the same place at the same time. In iron, the electrons are packed so tightly together, they vibrate to avoid being in the same place at the same time. The constant addition of matter from continuous silicon burning, results in there being too much mass to support, the Chandrasekhar limit is reached and the outcome is a supernova, pulsar or black hole.

A question and answer session was chaired by Brian Kelly who then thanked Dr Bill Samson for his excellent talk.

After coffee break the third session got under way, chaired by Dr Harry Ford of the Greenwich planetarium. He introduced to the meeting, Dr Tom Lloyd Evans whose talk was entitled Planetary Nebulae and Variable Stars. The intrinsic variables show changes in luminosity which are due to physical changes within the stars and there are several different kinds which show characteristic spectra and light curves. These are stars not on the Main Sequence and are often old ones exhibiting instability. Many lose mass by ejecting matter from their surfaces one or more times and luminous rings are formed as the gases are ionised by UV from the hot central star itself. Tom showed a series of wonderful photographs of planetary nebulae taken by the Hubble Space Telescope, many of them showing nearly symmetrical extensions on opposite sides of the star, the result of high-speed bipolar outflow, so that they appear like cosmic butterflies.

After a very nice lunch, delegates could either visit the satellite receiving station at St. Andrews University, or visit the town of Arbroath.

I decided on the trip to Arbroath which included a visit to the Abbey. We were given a short guided tour of the site.

Arbroath Abbey consists of the substantial ruins of a monastery, founded by William the Lion in 1178 and intended as his own burial place. It was the scene of the signing of the Declaration of Arbroath of 1320, which asserted Scotland's independence from England.

We then visited Arbroath's famous Old Red Sandstone cliffs. The scenery was remarkable and the sea although a flat calm away from the coast, could be heard roaring into the inlets which, over geological time, had been cut away by the power of the water. The noise was truly frightening and was ample demonstration of the raw power of nature.

All too soon it was time to return to Dundee for dinner, and to compare notes with the people who chose the alternative afternoon visit.

 

So many people wanted to visit the Satellite Tracking Station at Dundee University's Department of Electronics, organised by Brian Kelly, that two visits were necessary. It was a bit crowded, but everyone was impressed by the high-tech equipment. The data is received and processed from the meteorological satellites and Dundee's weather images are to be found everywhere. These include infra-red and visible cloud and surface maps of the British Isles often seen in the journal Weather.

Dr Mary Bruck with Ken Kennedy, Dawn Robertson and Dorothy Mackie
Dr Mary Bruck with Ken Kennedy, Dawn Robertson and Dorothy Mackie

Session four was opened by Lorna McCalman, President of the Astronomical Society of Edinburgh, who introduced the speaker for the evening, Dr Mary Brück.

Dr Brück spoke on The Spectra of the Stars

The history of spectroscopy was traced from the time, almost 200 years ago, when William Wollaston noticed some dark lines crossing the rainbow-like spectrum of the sun. Then Joseph Fraunhofer noted that there were seven lines which he assumed to be the divided colours of the rainbow. The story continued as Dr Brück told how William Huggins decided to compare laboratory spectra and stellar spectra. First visually and then photographically, he explored the spectrum of stars, nebulae and even comets.

As methods to examine the spectrum became more sophisticated through objective prism method and photography, a vast amount of information was gathered which needed to be sorted and analysed. This task fell to a group of women organised at Harvard by Professor Pickering, headed by Williamina Fleming, very appropriately born in Dundee, who was put in charge of sorting the stellar spectra into types. She devised a system of classifying stars according to their spectra, She herself sorted an incredible 10,000 stellar spectra surpassed only by her successor Annie Cannon who sorted a mind-boggling 400,000 spectra.

The next breakthrough came with the Hertzsprung-Russell diagram which graphically illustrated the stellar types. By the 1920s the theory of quantum physics was developed.

Since that time, spectroscopy, which analyses the interactions of atoms, ions and molecules with light of different wavelengths, has been a major part of astronomy. Dr Brück related how in her own professional career as an astronomer, she could remember the tedium of pre-computer calculations required in this field of work and how a seemingly small amount of raw data would result in many long hours of grinding calculations. Computers certainly revolutionised astronomy and made life very much easier.

After questions, Lorna McCalman thanked Dr Brück for her most enjoyable lecture. A fascinating talk given by a natural storyteller who held everyone spellbound.

We were invited by Dr Bill Samson, to visit the Mills Observatory where we received great hospitality. Tea, coffee and refreshments were laid on for us by the Friends of the Mills. In addition to that, they very thoughtfully arranged a (small) aurora display for us to observe! And several objects were seen through the 10-inch Cooke refractor.

Sunday morning brought the first rain of the weekend and my goodness, did it rain! There was some thunder and torrential downpours.

There was no way that the weather would dampen our spirits and session 5 was opened by Mike Fenwick, Chairman of the Dundee Astronomical Society. Mike introduced Melvyn Taylor who is Secretary of the Binocular Group of the BAA Variable Star Section to talk on Observing variable stars. Melvyn began by outlining the requirements for safe and comfortable variable star observing, The illustrated set-up, complete with reclining chair, looked very comfortable and well organised with all the things needed by the observer placed on a nearby table for convenience. This in stark contrast to my own setup which usually leaves me scrambling around trying to find where last I laid down the note book, which, when located has to be cleared of the slugs which invariably found it before me!

Melvyn Taylor then went on to outline the various types of binoculars that could be used and illustrated ways of mounting them onto a tripod. He then showed examples of variable star maps and explained how to use them and gave a few examples of stars which we might like to follow.

Melvyn showed the observing sheets, explaining how to fill them in as well as explaining why all the information was needed and the factors which could influence observers results. He then told us how the results were correlated and used to make light curves.

Mike Fenwick thanked Melvyn Taylor for his informative talk and we then had a coffee break which was followed by the final session chaired by Ron Livesey, Director of the BAA Aurora Section. This session was handed over to the delegates allowing time for short presentations.

This session was started by Dr Harry Ford who gave a short talk about Greenwich Time and how the time service had evolved there, with the transit telescopes and the clocks, and how the Greenwich Meridian became the standard for the world.

Next came Douglas Cooper, Secretary of the Stirling society, with a simple device a beanbag which in the absence of a tripod makes a stable mount for a camera, e.g. on a car roof. He also showed some recent aurora photographs.

Alex. Pratt from Leeds showed a light curve of the eclipsing variable RZ Cas from his own observations.

Dr Russell Cockman of the Falkirk association showed a magnificent collection of slides which he had taken using a simple camera drive and 35mm film from the clear skies of Tenerife. Astounding star-fields showing nebulosity, even on short exposures. We never get anything like this in Britain.

Walter Scott, also of AFA, showed pictures of the aurora of 7/8 Sept, the one we had seen from the Mills the previous night, which he had manage to process quickly as computer images.

Finally Tom Lloyd-Evans made some brief remarks on the amateurs' contributions to variable star research.

After lunch it was time to go home. Not only had we enjoyed the lectures and our visits on the Saturday afternoon, but we had enjoyed each others' company. I was not alone in feeling sorry that time had flown so quickly. As one person said as we waited for our train

"I really enjoyed the Dundee meeting. Everyone was open and friendly and chatted to me as if they'd known me for 10 years. In southern England they have to know you for 10 years before they'll acknowledge you!" And that comment captured the essence of the weekend.

Lorna McCalman