Star Gazing

Tuesday morning the UK will experience a partial solar eclipse. These are rare events and are worth seeing even though it won't be as dramatic as the one in 1999. However it can still be dangerous and the Department of Health's Chief Medical Officer has issued advice on "safe viewing" of this stellar event.

As the eclipse will occur between 8.00 and 9.30 in the morning, if the weather is clear then it will be easily seen by millions on their way back to work or school after the Christmas break.

During a previous eclipse in 2005 a young boy suffered damage to his central vision after looking directly at the sun, so it is important that everyone, children and adults, is aware of the dangers and the precautions to take.

Anyone who wants to experience the eclipse must do so either by indirect means or by using special eye protection. Just because you experience no pain looking at the eclipse does not mean that your eyes have not been damaged, so follow this advice to be certain of a safe viewing experience.

Direct viewing

• Sunglasses are NOT safe. They do not block the harmful radiation that causes eye damage.
• To directly view the sun, you need to use properly designed and certified solar filters. These will be identified as such, and should have the CE mark and a statement that it conforms to EC Directive 89/686/EEC. Alternatively a welder's glass rated 14 or higher can be used.
• Even with the correct filters in place children could still be at risk if the fitting is designed for an adult's face. These should only be used by children with fully trained adult supervision.

Indirect viewing

This is the safest way to see the eclipse. A simple home-made "pin-hole" camera can be constructed to view the eclipse. You will need two thin but stiff sheets of white cardboard.

• Make a very small, clean hole in one piece (with a sharp pin).
• Stand with your back to the sun.
• Hold up the sheet with the hole so that it is exposed to the sun.
• Place the second sheet below the first. An inverted image of the sun should be cast on the second sheet.
• To make the image brighter, move the screen closer to the pinhole.
• Do not make the pinhole wide or you will only have a shaft of sunlight rather than an image of the crescent sun. 

Remember, this instrument is used with your back to the sun. 

 The sunlight passes over your shoulder, through the pinhole and forms an image on the cardboard screen, beneath it. DO NOT look through the pinhole at the sun.

Under no circumstances should you look directly at the sun.

By all means watch this special event but do so safely!