BAA / RMetS Joint Meeting, 2004 November 27

 

The George Alcock Memorial Lecture

Dr Marsden opened, explaining that he had been travelling from his Boston home to a conference, and thought it very fortuitous that he had coincidently found himself in London on the day of such an enjoyable meeting. He announced that the 2004 Alcock Memorial Lecturer would be Dr Bill Livingston of the Kitt Peak Observatory, whose talk would be entitled Glorious Visions – Colour and Light in the Landscape. After spending time as a graduate student at Berkeley, Livingston had gone on to work for a time at the Mount Wilson Observatory, before becoming a Staff Astronomer at Kitt Peak, working primarily on image tubes as an engineer. However, with time he had made the transition, and become increasingly involved with his own scientific pursuits. Perhaps most notably, he had been President of IAU Commission 9 (Instruments) 1982-5. Dr Marsden recalled that Dr Livingston, always a keen amateur astronomer, had also taken part in many eclipse expeditions over the years.

Finally, before handing over to this year's speaker, Dr Marsden recalled some time ago a conversation he had had with writer Kay Williams concerning the possibility of writing a biography of the great observer to whose memory the following lecture was dedicated, George Alcock. Ms Williams, present in the audience, had thought this an excellent idea, and the fruits of her research had now been published under the title Under an English Heaven. In handing over to Dr Livingston, it gave Dr Marsden great pleasure to present him with a copy of this fine book.

Following applause, Dr Livingston recalled that George Alcock had always wanted to be remembered first and foremost as an observer, and so in the following talk, he explained that he would be describing many of the unusual atmospheric phenomena which he had observed around the site of the Kitt Peak Observatory. He opened with a discussion of a range of effects caused by shadows, ranging from the small, such as that of oneself projected forward onto mist on a foggy day, to some of the largest known, such as the dark blue band seen across the Eastern sky shortly after sunset, caused by the Earth's own shadow. He also remarked that shadows appeared unusually sharp when the Sun was only visible through a tiny crevice in the landscape. As a result, at sunset, there was a discernable difference between how horizontal and vertical features appeared, as the Sun's disk was truncated in one direction but not the other. Showing an image of the shadow of Kitt Peak onto neighbouring mountains, the speaker remarked that the shadow appeared triangular, with a sharp peak, even though in reality Kitt Peak was a relatively flat-topped mountain. This was a matter which had baffled him for some time, but he had eventually realised it was a general phenomenon: the shadows of all mountains appeared sharply-peaked.

Moving on to discuss rainbows, the speaker showed a range of unusual specimens, for example a pair of bows with different centres, one arising from direct rays from the Sun, and the other from its reflection in a lake. He also showed two rainbows of different sizes, coming about from the combination of freshwater rain and seawater spray, which, having differing refractive indices, produced bows of differing sizes.

Dr Livingston also discussed mirages – most often seen close to the ground on hot days, producing the familiar illusion of wetness. But he also explained that mirages could be seen next to any hot surface, and showed an example of the effect produced by an intensely hot concrete wall on a summer day, where a thin layer of very warm air had accumulated next to the surface. He also explained that if a temperature inversion layer formed in the atmosphere, where very warm air lay above much colder air, the familiar "wet-road" mirage might be inverted, and parts of the landscape appear in the sky. He showed an example of a mountainous horizon which appeared in double as a result of this effect.

The speaker has kindly provided a paper detailing the many other phenomena he discussed in his lecture, and for more detail the reader is referred to page ???.

Following the applause for Dr Livingston's discussion of such a curious range of phenomena, Mr Boles thanked him for giving a talk which was so relevant to Alcock's own interests, and so relevant also to the theme of the day's meeting: he had successfully combined physics, optics, astronomy and meteorology into a single talk. The meeting was opened to discussion, and a member pointed out, with reference to the speaker's earlier assertion that the shadows of mountains always appeared sharply peaked, that this was especially clear when observing peaks along the lunar terminator.

Mr Tom Boles then announced, on the subject of George Alcock, that the BAA had for some time been hoping to install a plaque to his memory in Peterborough Cathedral. Such a plaque had now been engraved, and had met the approval of the cathedral, and so it was hoped that it would be installed during the course of 2005 January. The meeting was then closed.

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Dominic Ford

Fairfield

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