BBC News Online: Sci/Tech

Viewing an eclipse

Looking directly through a telescope or other lens can blind you in an instant, and even looking with the unaided eye can cause permanent damage.

Experts advise viewers not to use ordinary sunglasses or filters. Some cut down the light but still let through enough heat to cook your eyes. The human eye does not have nerves so even if the eye is being damaged the victim will feel no pain as a warning.

The only safe filters are ones made of glass or mylar and specially coated with a metallic layer. These are available from specialist shops. Or some types of welding goggles can be used.

Seeing a partial eclipse safely

The safest way to view the Sun during the partial phase of the eclipse is by the projection method.

• Make a pinhole on a cardboard sheet big enough to allow the sunlight to pass through. The smaller the hole, the sharper but dimmer the image - a sharp pencil point is about right.
• Project the image of the sun onto a surface 1.5 m away, either a wall or another sheet of card.
• Or you can project a brighter image with a telescope or one half of a pair of binoculars - but remember not to look through the lens!
• A final way is to use a small mirror to project the image to a distance of about 10 m.

Relevant Stories

What is an eclipse? ( | Sci/Tech)
Shadow falls over South America ( | Sci/Tech)

Summaries

In this section

Vying for a name in cyberspace
Hackers penetrate Pentagon
Russian army gets wired
Shadow falls over South America
Brain repairs give new hope to stroke victims
Computers key to jobs success
Lung exerciser offers new asthma hope
A marriage made in cyberspace
UK government dithers on encryption regulation (From Special Report)
Computers come to life
Birthday could determine height