Ordinary Meeting and Exhibition Meeting, 2004 June 26
Members' Observations of the Transit of Venus, 2004 June 8
Mr James began by describing his own observations from Sharm el-Sheikh in Egypt, where he had been accompanied by BAA members including Mrs Hazel McGee, John Mason and Nick Hewitt. Having selected Cornwall as his observing site for the 1999 solar eclipse, he chose this site for the transit on the grounds that it had not seen a cloud in years, and rain perhaps only twice in the past decade. Whilst the heat of the Egyptian climate was quite formidable, and the seeing consequently rather poor, some observations were assured. In addition, accommodation was reasonably priced, Sharm el-Sheikh being a prominent diving resort.
Before showing his own images, the speaker showed a selection of his favourite observations from around the world – perhaps greatest of all a series of drawings by Mario Frassati, Director of the Mercury and Venus Section, showing what he saw at his eyepiece. Most notable were those of the appearance of egress, during which he saw light refracted by the atmosphere of Venus shortly after interior egress, generating a momentary bright outline to the dark limb of the disk of the planet. Another fine image was that by Tomas Maruska in Slovakia, who had been observing within a narrow track of locations which would see the International Space Station (ISS) transit Venus whilst it was transiting the Sun. The speaker explained that the ISS, whilst visible only infrequently in any one location, was always visible somewhere on Earth. Thus the transit of Venus by the ISS was not in itself rare, but merely required the observer to be in a very precise geographic location. The ISS took a mere 0.6 seconds to cross the solar disk, however, and so high-speed photography was essential if this was to be caught on camera. At his own observing site near Sinai, he was 70 miles to the south of the track where this phenomenon could be seen.
The speaker's own observations included a gripping six-hour video of the whole event, available on request on DVD. Owing to the time constraints of the meeting, however, there was sadly only time to show a time-lapse version of this video, compressed down to 45 seconds. It was noted that during the course of the transit, an unidentified object had briefly passed across the Sun. It did not appear to be any known satellite, and he invited members to get in touch if they thought they could identify it. The speaker also remarked that during the transit, he had taken his BAA Solar Viewer, as provided with the June Journal, into a swimming pool, but it had disintegrated in the water. It was noted with some humour that the meticulous safety instructions provided by the Public Relations Officer before the event had failed to warn observers of this hazard.
Sharm el-Sheikh had also been chosen by the BBC as an observing location, and professional observers were sent to provide footage to accompany that from Selsey. Mr James showed images of the setup they had used, which included Coronado solar telescopes fitted with cameras. Around a tonne of satellite uplink hardware was used to relay footage to London. However, he noted that the equipment was operated not by astronomers, but by experts in the filming of scientific events, without specialist astronomical expertise. As a possible result of this, they appeared to have missed first contact after initially training their cameras on the wrong limb of the Sun.
Mr James then proceeded to invite a series of members to present their own observations:
Nigel Evans had also observed from Sharm el-Sheikh, and showed a mosaic he had generated from a series of images taken with a webcam at intervals throughout the transit. As an intermission, he also showed images of the Milky Way he had taken in the desert, taking advantage of the dark skies. Using a Canon Digital SLR f/4 camera, and stacking six five-minute exposures, he had obtained a fine image. There was often debate as to how long film would remain useful to astronomers, and it seemed on the grounds of these images that it would soon be obsolete. He compared this CCD image with one of higher magnification taken on film, zooming in on Scutum. A little more detail was apparent, and so at present it seemed that film was marginally superior, but the difference was so small that it seemed unlikely to remain that way for long.
Mike Foulkes presented the results of his own observing trip to Egypt, on which he had been accompanied by Derek Hatch. He had sought to obtain high-resolution images of the black drop effect, but on the day, the seeing had been too poor to allow this. Though he had anticipated that it would be poor, it was to prove even worse than expected. At second contact, he noted that he could clearly see an arc of light around the dark limb of Venus, where sunlight was diffracting around its atmosphere. The black drop effect could be seen standing back, but was not apparent in the highest resolution images, suggesting it to be a seeing-related effect. In summary, he reported that his visual observations had been good, but his imaging less successful. Seeing had deteriorated during the transit, and become very poor by third and fourth contact.
Richard McKim reported on his observations from Northamptonshire, showing three still frames from an AVI video he had made. He had used a Hα filter. He remarked that his 14-month-old daughter's first reaction to being shown the transit was to try to rub out the blemish on the Sun's disk with her finger.
Neil Bone reported on his observations from Chichester, West Sussex, where he had used an unstopped 60mm aperture for solar projection. He had always previously been of the view that dictophones were a superb way to lose observations, but on this occasion had used one with great success to time ingress. At second contact he was unsure whether there had been a black-drop effect – if so it had been minimal. He recalled that a few years ago he had dreamt of observing three events: the Leonids of 1999, the total solar eclipse of 1999, and the transit of Venus of 2004. He was glad that clouds had spared him one of the three.
Stewart Moore had observed from East Anglia. He had found the weather so favourable, that not only had the seeing been superb throughout the transit, but it had also allowed for a full practice the previous morning. He had used an 8¼" aperture stopped down to 6", and noted that the seeing had been crystal clear at 6am. Rather than displaying more images, he wished to make three summary remarks: firstly how beautiful it had appeared through the eyepiece, secondly how huge Venus had appeared, and thirdly the lack of black-drop effect. With reference to the latter, he had perhaps been able to discern a fuzzy hair-like connection at second contact, rather like a meniscus effect. However, it had been much lighter than the dark disk of Venus, and did not interfere at all with his timing. He anticipated there would be much debate in coming months as to the origin of the effect which had so dogged historical observations.
Noting how fine the seeing had been, Mr Moore wondered whether amateurs ought perhaps to try solar observing at 6am more often. Finally, he reported that he had seen an effect similar to Bailey's Beads around the disk of Venus during the transit. This did not seem to have been seen by any of the other observers presenting reports, but he was curious to hear from anyone else who had seen a similar phenomenon.
Mr James concluded the presentation by showing images by a number of other UK observers, including Maurice Gavin, Lyn Smith, Martin Taylor, David Strange and Damian Peach. In Martin Taylor's images, it was noted that the black drop effect was seen in some of the webcam images. Normally only those images with good seeing were selected, and when this was done, the black drop disappeared. But when the opposite was done, and only the images with the poorest seeing selected, the black drop effect was clear. Mr James concluded from this that the black drop effect was very likely to be a seeing-related phenomenon.
The President concluded the proceedings by thanking the afternoon's speakers. He also expressed his gratitude to Nick Hewitt and Jonathan Shanklin for organising the meeting, and to Geoffrey Johnstone and Peter Hudson for providing assistance. Thanks also went to those members of the Cavendish staff who had been present: Harry Druiff, Bill Badcock and David Woosey, also to those who had helped in preparing the lunches. The meeting was then adjourned until the Out of London Meeting on Saturday September 10 in Douglas, on the Isle of Man.
© 2004 Dominic Ford / The British Astronomical Association.