Halo, halo, halo;Science

11th September 1998 at 01:00
It would take a galactic event to keep children at school during the summer holidays. Next year both will be the case, reports John Davies.

On August 11, 1999, clouds permitting, a total eclipse of the sun will be visible in Cornwall and Devon. It will be the first time for more than 70 years that this phenomenon has been seen on the British mainland.

Neil Tunstall, head of science at Helston School in Cornwall, has been preparing for the event more thoroughly than most, thanks to a Millennium Award grant. Earlier this year he and two Year 10 Helston pupils went to the Caribbean island of Curacao to view a solar eclipse and test equipment for next year.

It was a profound experience for him. "The corona (the outer white halo of the sun) seems to grow and grow; as your eyes adjust you see more and more, and all sorts of colours around. And you have these shadow bands crossing the landscape."

For viewing the sun directly in safety they found card-mounted mylar spectacles more useful than the ones they'd brought with them, which carried the European standard mark but were so light they were liable to blow off in a strong wind.

The total eclipse is more than just a time to stare in wonder, though. John Parkinson, a professor at Sheffield Hallam University and co-chairman of the UK Solar Eclipse Co-ordinating Group, says: "We're aiming to get as many people as possible to enjoy the eclipse, to understand what is going on and to get involved in some way."

This requires preparation. Neil Tunstall says: "There's about an hour-and-a-quarter of partial phases when the moon gradually covers an increasing amount of the sun's disc, then you've got your two minutes of eclipse, then another hour-and-a-quarter. We found that having some other activities to do kept us occupied and involved."

This is where a variety of projection methods come in. All involve positioning a small mirror, covered except for a small aperture about the size of a thumbnail, to reflect the sun on to a screen.

What varies is the way the mirror is mounted, which can be done using household objects. Helston pupils used an empty CD case, opened to allow for angle adjustment; a wooden coathanger (with a mirror taped to the hook, and one end of the hanger driven into the ground); and a flexible piece of card attached to the top of an upright lemonade bottle.

In Curacao they were able to view the changing outline of the sun before, during and after the eclipse on a screen which they had made by fixing white paper to some upturned benches.

Neil Tunstall says: "The children could draw round the images at intervals to record the progress of the eclipse. You can get an arc of images across the screen." He recommends a distance of about five metres between mirror and paper.

Although the big event will be happening during the school holidays, Helston School, like others in Cornwall and south Devon, will be open for most of that week. Neil Tunstall and his colleagues hope school parties from other parts of the United Kingdom will join in with their observations.

In the end, it will all hinge on one very British consideration: will the weather be kind? "I was down in Cornwall for August 11 this year and it was blisteringly hot," says an optimistic John Parkinson.

The Association for Science Education is producing resource packs for use in teaching science units related to the 1999 eclipse, which will be launched at the ASE's annual meeting in January, at Reading University. For more details call ASE on 01707 283000 or e-mail on ase@asehq.telme.com Sheffield Hallam University is also hoping to publish some activity packs for schools (provided someone will pay for production and distribution). Science Line (0345 600444) will answer questions on the eclipse. Information about other plans for the eclipse can be found at the official Web site: http:www.eclipse.org.uk Neil Tunstall can be contacted at Helston School, Church Hill, Helston, Cornwall TR13 8NR. E-mail: Helstonscc@aol.com A booklet, 'A Guide to the 1999 Total Eclipse of the Sun' by Steve Bell (which includes a free aluminised mylar viewer) is published by HMSO, price pound;5.95.

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