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Friday, 15 June, 2001, 09:41 GMT 10:41 UK
Solar eclipse: What happened in 1999
A satellite image shows the Moon's shadow on Europe's western edge
A satellite image shows the Moon's shadow on Europe's western edge
Europe and South Asia witnessed a total solar eclipse in August 1999, allowing scientists to study violent magnetic storms in the Sun's corona.

The drama is over and the Moon has passed over the Sun, but for scientists the work is just beginning.

From the UK to the India, they harnessed the darkness of the August 99 total solar eclipse to try to solve mysteries about the Sun and its effect on the Earth, generating masses of data which must now be interpreted.

How solar storms strike the Earth and knock out satellites, why the Sun's atmosphere is much hotter than its surface and how the Sun's heat drives the Earth's climate are just some of the questions the researchers are asking.

And new mysteries have also been thrown up. Professor Mark Bailey, Director of the Armagh Observatory, UK, observed the eclipse from Alderney in the Channel Islands. He told the BBC: "As the eclipse grew towards totality, we had very unusual phenomena in the sky. Two very dark bands stretched right across the sky, bracketing the Sun like parallel lines, which I have never heard reported before."

Champagne scientists

In the Romanian city of Ramnicu Valcea, where totality lasted longest, scientists from Williams College, in Massachusetts, US, cracked open bottles of champagne as the Sun began to reappear.

Scientist adjusting coeloscope
The 1999 solar eclipse will lead to greater scientific understanding
"It worked great," said Jay Pasachoff, director of the Hopkins Observatory at Williams College. Working from the roof of a hotel, he and colleagues carried out experiments on solar heating, the Sun's corona and the Sun's magnetic field.

The 1999 solar eclipse will lead to greater scientific understanding, largely because its track across Europe and South Asia allowed astronomers many vantage points with clear skies. Also, the Sun is nearing the peak of its 11-year activity cycle, so the corona should be more active than during previous eclipses.

The eclipse is an important scientific opportunity for two main reasons. Firstly, it completely cuts out the Sun's light for a short time which can be precisely predicted. This means that the effect of the Sun on the Earth's atmosphere can be measured.

Radio waves

For example, the ionosphere is a little-understood outer layer of the Earth's atmosphere. This is where the Sun's energy first affects Earth. Radio waves bounce off the ionosphere much better in darkness than in light, so they can be used to probe the behaviour of the enigmatic layer.

During an eclipse scientists can see the violent magnetic storms in the corona
Secondly, the Moon perfectly blocks out the body of the Sun, leaving its outer atmosphere, or corona, in perfect view. Normally, the Sun's intense light means the corona is nearly impossible to observe in detail.

During an eclipse, scientists can see the violent magnetic storms in the corona which might explain why the corona is two million degrees Celsius, whilst the Sun's surface is a relatively cool 6,000 degrees Celsius.

Even in areas where cloud blocked a clear view, scientific experiments were successful. At Land's End in the UK, Dr Barrie Jones, head of Physics and Astronomy at the Open University, was searching for waves of pressure changes in the atmosphere.

"These are believed to be generated because the Moon's shadow cools the atmosphere," Dr Jones told BBC News Online. "I know I'll have some good data and hope to detect these waves for the first time."

Cause and effect

Dr Jones's equipment is highly sensitive and has to detect pressure variations of just a hundredth of a millibar. These pressure waves are in the atmosphere all the time, generated by sunsets and sunrise and by the wind going over mountains.

Dr Barrie Jones said his experiments were not spoilt by cloudy skies
"They are important ways of carrying energy around the atmosphere and so of importance in the general understanding of weather," said Dr Jones, a veteran of five eclipses.

"The beauty of the eclipse is that you know exactly what is causing the waves, and where and when. So you can link a specific wave train back to a specific cause. Usually these waves are caused by such a mixture of events you cannot link cause and effect. This will give a much better understanding of the process."

Dr Jones's experiment worked well but was his enjoyment of the spectacle spoiled by the cloudy skies? Not at all. "It was actually very impressive, a great wall of darkness flying over the Atlantic towards us and really nice orange and pink colours around the horizon."

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