A Report by Eric H.Strach, F.R.C.S., M.Ch.Orth.,
Hon. Vice President,
Liverpool Astronomical Society
Members of the Liverpool Astronomical Society have been trying for many years to capture the elusive bands on photographs, cine film and more recently on camcorders.
I have first seen them at the eclipse of 1976 in Zanzibar. At that time Graham Broadbent constructed a special screen which he erected so that the rays fall vertically on it. It was an early morning eclipse, the sun and moon were only 8° above the horizon.
We have seen the bands on several subsequent eclipses but failed to record them on photographs or cine films. After Graham left our society I tried to continue his work and inherited his shadow band screen, and took it to Java in 1983, to Sumatra in 1988 but I did not succeed to record the bands. In 1990 was clouded out in Finland.
I had better luck on 11th July 1991 in the Baja peninsula: I mounted the camcorder to a fitment beneath the apex of my tripod so that it pointed downwards to the ground, where the screen was placed at this mid-day eclipse with the sun almost overhead. The bands were seen but only with the eye of faith could one possibly make out the bands in the recording and I was never convinced.
I had to miss the next three eclipses but I tried the experiment again at Knipbaai Beach in Curacao on 26th February 1998. The sun was again high at the time at an altitude of 60° so I used the same arrangement. The bands were clearly seen by most observers and I just hoped that my new camcorder fitted with a “high 8” video cassette will succeed.
The camcorder was started 4 minutes before second contact and a one second time generator gave signals which changed pitch every half-minute. Thus the signals and any comments were recorded for later analysis. I used a polaroid filter combined with an UV filter. My recording was stopped some 4 minutes after third contact.
I suppressed my curiosity and refrained from playing back what I recorded. Only on the day after arriving home did I play back the video and there was no doubt whatsoever that the shadow bands were there, visible for 32 seconds before totality and 27 seconds after totality. However, the bands remained visible for over one minute.
They moved rapidly across the screen in a direction from E to W before second contact and from NNE to SSW after third contact. The bands were disposed at an angle of 70° to the E-W line before 2nd contact and at 30° after 3rd contact – as illustrated in the diagram. Slow motion studies of the video showed that the bands merged at times and on occasions they seemed to move in opposite directions, undoubtedly a stroboscopic effect.
The question arises why I succeeded this time and not on any previous attempts. Perhaps the use of the polaroid increased the contrast, I doubt whether the UV filter had a similar effect. The most probable explanation is that the bands were more pronounced this time. Further attempts should be made to record these bands in the future but it may take several eclipses and thousands of miles of travel to get results. It would be far better to have a battery of like-minded observers who would use different systems and filters to establish the optimal method.
The images display on this page were obtained by a frame grabber and were then image-processed. My grateful thanks for their help in this process go to Mr Andrew Trafford of Liverpool University and to Gerard Gilligan and Robert Johnson of Liverpool Astronomical Society.
All observational images and diagrams are © Eric Strach and used with permission.
I have a little shadow that goes in and out with me, and what can be use of him is more than I can see.
From “A child’s Garden of Verses” by Robert Louis Stevenson – 1885
Further Reading List:
- Brewer,B. Eclipse. 2nd ed pub Earth View. 1991.
- Codona J.L. The Enigma of Shadow Bands. Sky & Telescope Vol 81 May 1991. PP482-487.
- Jones Barrie W. Shadow Bands during the Total Eclipse of 3rd Nov 1994. J of Atmosph & Terrest Physics, Vol 58 pp 1309-1316 1996.
- Jones J.E. The Observations of Solar Eclipses – Getting Started in Astronomy series. pub Liverpool Astronomical Society. 1995.
- Maunder M. & Moore P. The Sun in Eclipse -(Practical astronomy). pub Springer-Verlag. 1998.
- Marschall L.A. Shadow Bands – Solar Eclipse Phantoms. Sky & Telescope Vol 67 Feb 1994 pp116-118.
- Williams S. UK Solar Eclipses from Year 1. (an anthology of 3,000 years of solar eclipses). pub Clock Tower Press. 1996
- Zirker J.B. Total Eclipses of the Sun. pub Princeton University Press. 1995.