Seeing a total eclipse is a fantastic experience. But without proper preparation it can also be very dangerous to the eyes.

No pain does not mean no damage

Viewing the partly eclipsed Sun without protective equipment will result in a retinal burn.

Depending on how long the retina is exposed to the Sun, this injury may cause permanent damage to vision.

There is no pain when the retina is being burned, and the resulting visual symptoms do not occur until at least several hours after the injury has occurred - by which time it is far too late.

This photograph is the back of the eye of a man who viewed the partial solar eclipse of 1966 without eye protection. The arc-shaped scars are typical of an eclipse burn, and the vision in this eye has been reduced to 20/30 (6/9).

This picture shows a more extreme form of solar retinopathy in the left eye of a young man who stared unprotected at a partial eclipse of the Sun.

Several crescent-shaped burns can be seen in the central retina, and these have resulted in blindness in this eye, with his vision reduced to below 20/400 (6/120).

How can you view the eclipse safely?

Totality rarely lasts longer than a couple of minutes, depending on your location on the eclipse path; and for most people, only a partial eclipse will be visible. Although the sky will become very dark, it will not be safe to look at the Sun without proper equipment and viewing techniques.

Indirect viewing

Most health professionals recommend the simple pinhole viewer. You can make this with a cardboard box or with two pieces of stiff card. Punch a tiny hole in one of the cards and, with your back to the Sun, hold the card up so that light falls through the hole, projecting an inverted image on to the other card. Do not look at the Sun through the pinhole.

Direct viewing

Many eclipse watchers may want to view the totally or partly eclipsed Sun directly.

Viewing the partial eclipse in London in 1954 - how not to do it

Special eclipse viewers made of either aluminised polyester or a very dark polymer material are available but these cannot be guaranteed to be totally safe.

The filter material is usually mounted in a cardboard frame that can be worn on the head like eyeglasses, or held by hand in front of the eyes. Which design you use is a matter of personal preference, but viewers bearing the "CE" mark from Europe may be more safe. If you do choose to use a viewer, always follow the manufacturer's advice. A shade number 12, 13, or 14 welder's filter can also be used.

Don't use dangerous substitute filters

Materials that should not be used as solar filters include:

Sunglasses

Photographic neutral density filters

Smoked glass

Polarizing filters

Compact discs

Floppy disk media

Black colour film

Any black and white film negatives bearing images.

Children's safety

The spectacle-shaped viewers may be too large to be worn securely by some children. While older children may wish to use eclipse viewers, very young children should only watch the eclipse on television, or with an indirect viewer. All children should be closely supervised while watching an eclipse.

A total eclipse is a beautiful sight to behold. Enjoy watching it safely.

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This page has been written with advice from the UK's Particle Physics And Astronomy Research Council (PPARC), the Department of Health, the BBC's Chief Medical Officer and Professor Ralph Chou, who also supplied the pictures. It was prepared for the 1999 solar eclipse and updated for the 2001 eclipse visible in southern Africa.