by Dr. John Eric Jones
The LAS have been sending members on total solar eclipse expeditions since the 1880’s. One saros ago no less than 15 members went to Kenya to observe approximately 4 minutes of totality. This was a pivotal eclipse. Although there was already much experience of eclipses amongst some members, it was the first eclipse at which several experiments were deployed which have continued regularly to the present day.
This year a dozen members went to sites in Venezuela and Curacao to observe the eclipse of February 26th. The great majority went to a beach at Knipbaai in the far North-West of Curacao. At this location, apart from photography, the two main experiments were timing the duration of totality and attempting to video shadow bands if they occurred.
Shadow bands are notoriously difficult to photograph or film. In 1976 Graham Broadbent of the LAS obtained photographs of them at an eclipse in Zanzibar as displayed on a standard 1 metre diameter shadow band disc. The disc follows the practice of Edgar M.Paulton and Richard L.Feldman. The latter studied shadow bands for over 40 years (see Sky & Telescope, Vol 39, No2 February 1970 pg 132-133). In recent years Eric Strach (or rather Mrs M.Strach!) took on the onerous task of hauling shadow band discs across the globe to eclipse sites usually without success. A faint video image was recorded in 1991 but this year marked a crowning achievement as distinct shadow bands were recorded both before and after totality. Video frames and a report have appeared on the LAS web site through the courtesy of LAS member Mr Gerard Gilligan who arranged processing of the video at Liverpool University.
Unfortunately Eric Strach’s vocal signals at 2nd and 3rd contacts were drowned on his tape by shouts of excitement of the surrounding observers. However another timing experiment was performed by LAS member Eric Jones at a different location. Because of this very fact of background noise, Eric Jones accepted an invitation from Professor John Parkinson (Sheffield Hallam University) to view the eclipse from a quiet site at the Knip Landhuis ( a rather elegant Plantation house roughly 2km from Knipbaai) Another possible location was next to the official public viewing site at Watamula in the very north of the island where under Professor Parkinson’s direction a gigantic wall of cargo containers, stacked two high, had been positioned to protect observers from the constant trade winds which sculpt the local low thorn bushes into fantastic shapes.
However as eclipse day dawned with local cloud cover and rain it was decided to change site as Knip Landhuis was under a plume of clouds generated by the local St Cristoffelberg mountain. It was therefore decided to use a villa at the Kadushi Cliffs Resort just north of Westpunt. As we set up, our activities were filmed by the BBC for a possible program to be broadcast in the UK before the 1999 eclipse. Colin Davies and Eric Jones occupied the balcony of the villa whilst the BBC and John Parkinson’s group occupied the patio in front.
Fortunately as the morning proceeded the sky cleared and by the time of the eclipse the sky was perfectly clear. We were confident that the sky would be clear, as a ship (The Holland- America Line Statendam) anchored near us just a few hundred metres offshore. They presumably had weather satellite systems and so the fact they had selected our location meant we were in a good spot.
We viewed the usual pre-eclipse phenomena. The BBC filmed crescents on the balcony floor underneath a plastic plant held high in the air by Colin. Shortly before totality a parrot-like bird crashed into the balcony next to Colin and the video camera. The bird was obviously disoriented by the eclipse and so Colin tried to soothe it. About 30 seconds before totality the cry “shadow bands” went up and a quick glance revealed a magnificent display of shadow bands visible not only on a small shadow band screen next to me but also on the white-washed walls of the villa.
In addition to the timing experiments a programme of still photography was carried out. In fact it proceeded so well that an extra bulb exposure was added. It is easy to lose track of time during totality so a series of electronic alarms had been set up as a reminder. This allowed a full 50 seconds of spare time to look around to enjoy the near-minimum style of corona, the nearby planets and the environment which was enlivened by the explosions of fireworks.
Three different timing methods were used:
- Motorised electronically controlled camera.
- Vocal signals recorded onto tape together with time signals.
They all worked perfectly.
We also received further data from other locations. At Knipbaai the President of the British Astronomical Association, Martin Mobberley took a video which provided an extra timing. Also at the same location Mr. Shelley Fey who is an experienced eclipse observer and whose timings have been a valuable supplement to our own data at previous eclipses provided a further measurement of the duration of totality.In fact we also received a video with associated GPS measurement from yet a third location on the island of Curacao.
Timing experiments, when analysed, can yield information on possible solar diameter variation. The analysis of these timings is now almost complete but they all give a very consistent picture that the solar radius was about 0.4 arc-seconds larger than the adopted IAU value at the time of the eclipse. This is from 6 different measurements using 4 different techniques at three locations. The consistency was very satisfying.
There was one final bonus after all the excitement of the eclipse itself. After most people had returned home, Colin Davies and Eric Jones lingered on in Bonaire. At approximately 9.17pm local time on the 14th March they were treated to an occultation of Aldebaran close to the southern limb of the Moon which was recorded on video. This brought a very successful eclipse expedition to a close.