Stargazers in south and central Africa will be treated to a spectacular solar eclipse Thursday when the Moon wanders into view to make the Sun appear as a "ring of fire", astronomers say.

The phenomenon, known as an annular solar eclipse, happens when there is a near-perfect alignment of the Earth, Moon and Sun.

But unlike a total eclipse, when the Sun is blacked out, sometimes the Moon is too far from Earth, and its apparent diameter too small, for complete coverage.

"At the eclipse's peak, all that will be visible is a ring of light encircling the black disk that is the Moon," said astronomer Pascal Descamps of the Paris Observatory, in the French Indian Ocean island of Reunion to witness the event.

"That will be the magic moment," he told AFP.

Daylight should be slightly dimmed, as on a very cloudy day.

Only people along a very narrow, 100-kilometre (62-mile) band stretching across central Africa, Madagascar and Reunion will see the full effect of the ring, or annulus.

Anyone north, south, east or west of the band will see only a partial eclipse, or none at all.

The display will start at 0613 GMT in the south Atlantic, passing over Gabon, the two Congos, Tanzania and the northern tip of Mozambique and Madagascar.

Reunion island will get a good view before the eclipse ends around 1200 GMT over the Indian Ocean, said the Paris Observatory.

At the eclipse's peak, between 1008 and 1011 GMT, the Moon will cover about 94 percent of the Sun.

- Protect your eyes -

The experts warn that sunglasses offer insufficient protection for looking at the Sun, even when it is partly masked.

"Looking at the Sun without special protection, even for a few seconds, can cause irreversible damage to the retina", even blindness, said Descamps.

Special eclipse glasses can filter out the Sun's harmful ultraviolet and infrared rays.

One could also use a pinhole camera, which can be easily built at home -- basically a box with a hole on one side for light to pass through and project an inverted image on the opposite side.

Source: AFP