Solar science

An expedition to observe an eclipse in 1919 measured the position of stars during totality and confirmed Einstein's prediction.

Watching from space

Today, most of the scientific study of solar eclipses focuses on the Sun's superheated outer atmosphere - the corona. This is normally difficult because of the ferocious glare of the Sun, but when the Moon blocks out the glare, the surrounding corona is revealed in glorious detail.

For this particular eclipse, several spacecraft will be studying the Sun from orbit, notably the Solar and Heliospheric Observatory and the Japanese satellite Yokoh, as well as the recently launched Transition Region and Coronal Explorer satellite.

The corona is a layer of thin gas at a temperature of many millions of degrees. It lies over the Sun's visible surface, which is at a relatively modest 6,000 degrees. Just how the corona gets so hot is a mystery.

Eclipse experiments

So scientists will be looking for patterns in the inner corona that may be shock waves bringing energy up from below.

They will use the satellite observations and high-speed cameras on the ground.

Some scientists believe that rapidly-oscillating magnetic waves are generated by turbulence in the Sun's upper layers. These may travel along magnetic loops for hundreds of thousands of kilometres and violently whip up the heat of the corona. Researchers hope to photograph these loops in action.

Another experiment will look at the large-scale structure in the corona over the entire duration of the eclipse.

Astronomers do have instruments that simulate an eclipse by artificially blocking out the Sun's disc but nothing gives them as good a view of the corona as a real solar eclipse - as long as it is not cloudy.

The 1999 total eclipse can be viewed on 11 August.