'Ring of fire' eclipse treat for southern skygazers

Paris - A spectacular "ring of fire" solar eclipse on Sunday will regale skygazers in South America and southern Africa, with seafarers in the nearby Atlantic getting a front-row view too, astronomers say.

The eclipse - during which the Sun will all but disappear as the Moon crosses its path - will be most visible in a 100km band cutting through Chile, Argentina, Angola, Zambia and the Democratic Republic of Congo.

A so-called annular solar eclipse occurs when the Earth, Moon and Sun line up.

But even when perfectly aligned, the Moon is too far from Earth to completely block out the Sun, creating instead the impression of a fiery ring.

Change in quality

At first, it will look as if a "bite" has been taken out of the Sun, said Terry Moseley of the Irish Astronomical Association, stressing that viewers should not observe the eclipse unfold with the naked eye.

"This 'bite' gradually gets bigger and bigger as the Moon - which is itself invisible - moves further and further in front of the Sun," he said.

"As about 90% of the Sun is covered, you'll notice a distinct drop in temperature and brightness and a change in the quality of the light which is hard to describe."

As the day darkens, birds and animals may enter a night-time routine, thinking sunset is nigh.

At the height of the eclipse the Moon will be right in the middle of the Sun, leaving "a perfect, beautiful, symmetrical ring" of light around the edge before exiting on the other side, said Moseley.

For people just outside the band of optimal viewing, the phenomenon will appear as a ring thicker on one side than the other, said Moseley - "not symmetrical, but still an amazing sight."

Anyone further afield will see little or nothing.

Potential spoiler

It will take about two hours for the Moon to move across the face of the Sun, but the "ring of fire" peak will last a mere minute.

Weather is the only potential spoiler.

Nasa's eclipse website recommends watching the weather forecast a day or two before the eclipse and picking somewhere with a cloud-free prediction.

"Good weather is the key to successful eclipse viewing - better to see a shorter eclipse from clear sky that a longer eclipse under clouds," it says.