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Last Updated: Friday, 30 May, 2003, 21:33 GMT 22:33 UK
'Ring of fire' coming
An annular eclipse of the Sun occurs this Saturday.

ZONE OF ANNULARITY
Map BBC
Darkest (antumbral) shadow sweeps east to west from Scotland
Most of Europe, Middle East, and Asia to get partial eclipse
Next total solar eclipse in November is viewable only Antarctica
The event, which will see the Moon slip in front of the Sun's disc, will throw a dark shadow on the North Atlantic region. It is timed to last from 0345-0431 GMT (0445-0531 BST).

Annular eclipses are not quite as spectacular as total solar eclipses because the sky never goes completely black.

Viewers with the correct equipment will instead catch a brilliant ring of sunlight around the Moon. Under no circumstances, say astronomers, should people look towards the star with the naked eye; blindness could result.

The "path of annularity" across the Earth's surface begins in northern Scotland, and then sweeps across Iceland and portions of Greenland.

The point of greatest eclipse is timed for 0408 GMT. At this point, the axis of the path is 60 kilometres (37 miles) out at sea, northwest of Iceland.

A partial eclipse, in which the Moon just takes a bite out of the side of the Sun's disc, will be seen across a much broader region.

Most of Europe (except Spain and Portugal), the Middle East, as well as central and northern Asia, are favoured here.

Proper equipment

Not every eclipse can be total. The Moon's orbit around the Earth is not perfectly round; the satellite's distance from the planet varies from about 356,000 to 407,000 km (221,000 to 253,000 miles).

This difference makes the Moon's apparent size in our sky fluctuate by about 13%.

SCOTTISH ANNULAR ZONE
Map, BBC
Find flat, cloudless north-east horizon to view eclipse
Coastlines or hills are best locations
Only use protected optical equipment or approved glasses
Under no circumstances squint at Sun with naked eye
If the Moon happens to eclipse the Sun on the near side of its orbit, it totally blocks out the star (a total eclipse). But if the Moon eclipses the Sun on the far side of its orbit, the satellite will not completely obscure the star's disc - and a "ring of fire" or annulus of sunlight is seen.

The effect is to throw an "antumbra" or "negative shadow" on the Earth's surface as the Moon moves across the face of the Sun. It is the track of this antumbra that is referred to as the path of annularity.

And although the daylight will significantly dim for those in this path, a substantial portion of sunlight will still be visible and potentially highly dangerous to anyone tempted to squint at the eclipse.

Unless you have access to a telescope or binoculars equipped with proper solar filters, or approved eclipse glasses, the advice is to use a pin-hole camera technique to project the eclipsing Moon and Sun on to a piece of paper.

High hill

This particular annular eclipse is slightly unusual because the antumbra has a very high, northern track across the planet, and the northern edge of the negative shadow actually misses our planet.

In fact, some rare celestial geometry means the track of annularity has a peculiar "D" shape.

What is more, this path runs from east to west rather than the west to east direction to which we have become accustomed with so many eclipses.

The Scots will be the first to catch the event. This is a sunrise eclipse and they will need to find a flat, cloudless north-east horizon to get a good view. A high hill or coastal location would be ideal.

Time-lapse annular eclipse, SPL
Sunlight catches mountainous peaks on the lunar limb to give the ring a beaded appearance
The Moon's antumbral shadow first touches down at 0345 GMT (0445 BST) about 100 km (62 miles) north of Glasgow.

It then moves in a northwestern trajectory, which stretches across Loch Ness, the Isle of Lewis (Outer Hebrides), Orkney Islands and Shetland Islands.

The shadow's edge reaches the Faeroe Islands at 0351 GMT where annularity lasts 03 minutes 08 seconds.

By 0359 GMT, the shadow reaches the southeastern coast of Iceland. From Iceland, it then races across the Denmark Strait, and bisects Greenland, where over a third of the enormous island lies within the track.

Just before reaching Baffin Island, the negative shadow leaves Earth in the Davis Strait at 0431 GMT. From start to finish, the antumbra's entire sweep lasts a little under 47 minutes.

There is a total solar eclipse this year on 23 November but it will only be visible from Antarctica. A partial eclipse will be visible though from parts of Australia, New Zealand and South Africa.

Have you witnessed the eclipse? Send us your comments using the form below. If you have any pictures please send them in jpg form to yourpics@bbc.co.uk.


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WATCH AND LISTEN
The BBC's Sue Nelson
"If the weather holds, Shetland is in for a treat"



SEE ALSO:
Moon dives behind Earth
16 May 03  |  Science/Nature
Mercury passes across Sun
07 May 03  |  Science/Nature
Millions wonder at southern eclipse
04 Dec 02  |  Science/Nature


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