By BBC News Online Science Editor Dr David Whitehouse

Stand by for an assault on all your senses. A total eclipse of the Sun is a unique experience - some say a little unnerving. You will get the most out of the event if you know what to expect.

There are periods when little appears to be happening, but it is over very quickly, so make sure that you take in the full spectacle when the action starts. Immerse yourself!

First contact

A tiny notch appears at the Sun's limb. The exact moment for this can be calculated, but it takes 10 seconds or so to notice it. For an hour and a half, the Moon creeps across the Sun. But for most of that time there is no perceptible diminution in the light or fall in temperature. Don't get a crick in your neck just yet - the best is still to come.

The crescent

The next stage is the crescent. Stand under a tree or near a bush and the gaps in the foliage will act as tiny pinhole cameras creating images of the crescent Sun on the ground. As the wind moves the leaves, the ghostly images dance around you. An old-fashioned cheese grater - one with just a single sheet of metal - will create the same effect.

Shadow bands

Then come the shadow bands. These are the atmospheric equivalent of the ripples of light that can be seen at the bottom of a swimming pool.

As totality nears, things start to happen more quickly: The sky darkens, the temperature falls, the shadow of the Moon will race across the surface of the Earth. No wonder primitive man believed the end of the world was at hand.

Second contact

We are heading into totality. The last sliver of the Sun's disk is about to vanish. A single, glorious burst of light - a diamond ring - appears briefly and then disappears. We have reached the second contact. The Earth is dark, the birds are in confusion, bats may come out and streetlights may come on automatically. Around the Sun its magnificent outer atmosphere, the Corona, becomes visible. Look around - you will see stars and planets.

Baily's beads

The Moon's limb is not smooth: there are mountains and valleys and sunlight may shine down them, producing flickers and flashes of light. This effect is called Baily's Beads after the English astronomer Francis Baily.

Then totality ends and the diamond ring is seen once more, briefly signalling the end of the most dramatic part of the eclipse.

Anti-climax

For many, the Moon's slow passage off the face of the Sun is now something of an anti-climax. Everyone will be talking about those two minutes of totality. It is an extraordinary event that will not be repeated again in the UK for many years.

This page was prepared for the 1999 total solar eclipse on 11 August. The next total eclipse can be seen across southern Africa on 21 June, 2001.