Historical Section meeting 2022
The 2022 British Astronomical Association Historical Section Meeting was held at 14:00 BST on 2022 May 14. It was in the form of an on-line webinar hosted by our Section Director, Mike Frost. There was only one speaker, Dr. Wayne Orchiston of the University of Southern Queensland, Australia. His subject was Asian Observations of the 1868 August 8 Total Solar Eclipse. This eclipse had the exceptionally long maximum duration of 6 minutes and 47 seconds. It can be viewed as a watershed as new observing equipment and techniques in the form of spectroscopes, polariscopes and photography enabled a more accurate record events to be captured than ever before.
The eclipse ground track passed from Arabia to India to the Malay peninsula. Observers from the imperial powers in Europe travelled to the region to observe the event, but what did they achieve? Well, they photographed the solar chromosphere and corona and many saw what was dubbed the ‘great horn’, a monstrous solar prominence some 141,000km (87,500 mile) high. To put this in context, it is some 10% of the solar diameter. Some observers thought they could detect helical motions within it. Polariscope observations demonstrated the corona to be of solar origin, and not lunar or terrestrial.
The French observers included Édouard Jean-Marie Stephan (1837-1923) and Georges Rayet (1839–1906), but they missed making discoveries on this occasion. Although they were experts in stellar spectroscopy, their lack of experience in solar work counted against them.
Norman Robert Pogson (1829-1891), director of the Madras observatory, identified seven emission lines in the solar spectrum. One was ‘near’ but distinct from the sodium D line, and Pogson suggested that this ‘line’ was a new discovery. However, publication of his results was delayed and eventually only three copies were printed. Was George Biddell Airy responsible for the delay? He coronium stifled Pogson’s career at other times too. Pierre Jules César Janssen (1824-1907) observed the eclipse from near Madras in India and saw the same bright emission line as Pogson. Janssen is now co-credited with the discovery of Helium, which is the real source of the ‘coronium’, along with the British astronomer Joseph Norman Lockyer.
King Rama IV (1804-1868, known as Mongkut pre-coronation) used the eclipse to inform the imperial powers of Britain and France of his fierce independence. He himself carried out calculations to demonstrate that the eclipse would occur and would pass over his territory. However, his choice of observing site was a poor due to swampy ground nearby which was a breeding ground for malaria carrying mosquitoes. He caught the disease and died on October 1. His achievements are memorialised in The King Mongkut Science Park.
Away from mainstream astronomy, a Mr. Pierre (or a Pierre somebody) reported seeing vertical lines of graduated colours near his horizon, although no explanation for what he saw has ever been produced.
Wayne sprinkled audience participation questions through his presentation to which he provided the answers at the end.
The unseasonably sunny weather limited attendance on the day but the recording on the BAA YouTube channel has proved popular and is available to watch at https://m.youtube.com/watch?v=XbD3gyQi7UY
Dr. Wayne Orchiston also acknowledged the work of his wife, Darunee Lingling Orchiston in the research which the talk was bade on.
The meeting closed at 15:45 BST.
Many thanks to Andy Wilson for efficiently making the technology work for us.
King Rama IV and his party observing the eclipse
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