Never mind the 15m land mines, we must see the eclipse

July 20, 2001

Nothing was going to keep the world's scientists away from Africa and from trying to solve the sun's greatest mystery. Aisling Irwin reports

Scientists still travel thousands of miles to spend fleeting minutes studying total solar eclipses - despite there being several high-tech instruments in space that command superior views of the sun.

These instruments have transformed solar science into one of the most exciting areas of astronomy. Paradoxically, however, they have revealed a mystery that seems solvable only through ground-based measurements.

That is why, on June 21, Ken Phillips, of the CLRC Rutherford Appleton Laboratory in Didcot, Oxfordshire, was to be found on the roof of the University of Zambia in Lusaka. Down the road, atop the Intercontinental Hotel, Jay Pasachoff, director of the Hopkins Observatory at Williams College, Massachusetts, was also running experiments.

Teams from India, Romania, the Czech Republic, Portugal, France, Slovakia and Poland were distributed along the path of totality, in Zambia, Zimbabwe, Mozambique and Madagascar. A couple of teams even braved Angola's civil war and 15 million land mines to take advantage of the highest chance of clear skies and the longest period of totality.

Their aims were varied, but some of the teams were bent on solving the sun's greatest mystery. The temperature of its thermonuclear core is 15,000,000C. Its surface is much cooler, 6,000C. But travel 3,200km more out, to the wispy white corona that makes eclipses so spectacular, and the temperature soars again, to 2,000,000C.

It is thought that heat from the core travels across the expanse of cool atmosphere as energy funnelled along the magnetic fields that loop and arch from the sun's surface. One theory is that the jostling surface layers set these loops vibrating and energy travels along them as along a violently cracked whip.

For this to be the case, theorists have calculated that the loops should be vibrating at a speed of once a second or more. Spotting such fast vibrations is beyond the data-collecting capacities of such in-space instruments as Soho, the European Space Agency's Solar and Heliospheric Observatory. The key, then, is to take pictures from the ground. Phillips used two state-of-the-art electronic cameras, each capable of taking 40 frames a second.

The days leading up to the eclipse were ominously windy and cloud-filled, and the researchers fretted as they set up their rooftop experiment. But June 21 dawned clear and still. When totality began, spectators on the roof jumped around, wobbling the first images. "But it was very successful in the end," Phillips says. In the three minutes and 13 seconds, they took 16,000 images - which will take a year to process.

But for Pasachoff, veteran of 21 total solar eclipses, disaster awaited. At the crucial moment there was a computer failure and his team was unable to make its images. "We are very disappointed, of course," he said. Three other experiments of his went smoothly.

Pasachoff will now have to wait for the next total solar eclipse, in December 2002, before he can make progress in solving the sexiest mystery of astrophysics. By coincidence, that eclipse also passes over southern Africa.

Aisling Irwin is editor of Africa & Madagascar, Total Eclipse 2001 & 2002 (Bradt Publications 2000), a guide to the two southern African eclipses.

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