June 5, 2001. Copyright 2001. Graphic News. All rights reserved.

SunÕs cosmic ballet over Africa

LONDON, June 5, Graphic News: Lusaka will get its moment in the sun -- by being cast into darkness -- as hundreds of foreign scientists and amateur astronomers descend on the impoverished Zambian capital to observe the first total eclipse of the sun of the new millennium.

On June 21 the rare astronomical show will send the moonÕs shadow streaking across the South Atlantic, and into southern Africa, before ending at sunset in the Indian Ocean.

A solar eclipse is truly a gift of nature, astronomers say. Through some fluke, the moon is the right size and at the right distance to precisely block all but the corona, the flaring outer envelope of the sun, which is a million times dimmer than the solar centre.

When the moonÕs orbit carries it between Earth and the sun, a shadow is cast onto Earth that causes momentary deep twilight. For those seconds of totality, the corona can be viewed and analyzed scientifically.

The path of the umbra -- the 125-mile-wide (200km-wide) centre track where the moon precisely shadows the body of the sun -- will begin as the MoonÕs shadow touches down in the South Atlantic Ocean at 09:33GMT, just off the coast of South America.

A partial eclipse of the sun will occur across a much broader band. Known as the Òpenumbral shadow,Ó approximately 4,300 miles (6,900 km) in diameter, the partial eclipse will be seen from Sub-Saharan Africa in the north to South Africa in the south. The MoonÕs dark umbral shadow will sweep across the Earth at velocities of 1,250 miles per hour (2,000 km/hr) or more.

To see the total eclipse of the Sun, one must be located in the narrow path of the umbra. Because the umbra is so small and is moving so quickly, the total eclipse lasts no more that 4 minutes 56 seconds from any location along its entire path.

For scientists, the five minutes or so of total eclipse represents a precious opportunity to probe the sunÕs corona, the fiery outer layer, and see things about the solar systemÕs star that are impossible to view at other times.

However while a total eclipse can be safely viewed with the naked eye, a partially obscured Sun can cause permanent retinal damage and Òeclipse viewersÓ that filter out hazardous rays should be worn.

Douglas Duncan, an astronomer at the University of Chicago, says there are three safe ways to look at the sun, starting with glasses with special filters.

A second way is to poke a pinhole in one piece of paper and hold a second piece of paper about a foot (30 cm) below.

ÒYou get a little teeny, tiny round image of the sun," says Duncan. That small image will turn to a crescent as the eclipse occurs. ÒPoke six pinholes and youÕll get six images.Ó

A third way is to use a pair of binoculars -- but do not look through them.

ÒPoint the fat end of the binoculars at the sun and youÕll find an image comes shining out of the eye-piece just like a projector,Ó he said.

From start to finish, the penumbra takes a little over five hours to sweep across the Earth. The umbra itself takes just over three hours to travel from the South Atlantic, through southern Africa and Madagascar before ending at sunset in the Indian Ocean.



On the web: Details of the times, duration and location of the eclipse, as well as other background material, is available at http://sunearth.gsfc.nasa.gov/eclipse/OH/OH2001.html
/ENDS
Sources: Reuters, Associated Press