THOUSANDS OF British schoolchildren have been told to turn their back on next month's total eclipse, or risk permanent blindness.
Unless people turn away from the sun - even when it is obscured by the moon and darkness falls - they could face devastating eye damage.
Children have also been warned that badly-fitting cardboard "solar glasses" could also leave them exposed to damaging radiation.
Up to half a million people, many of them pupils on school trips, are expected to descend on Cornwall on August 11 in order to witness the first total eclipse visible in Britain in more than 70 years.
"It takes only seconds to cause the damage, and you won't even know it until it's too late," said Rebecca Mullen of the charity, Fight for Sight, which is issuing cardboard pinhole boxes, allowing pupils to view the eclipse safely with their backs turned.
If they look at it directly, UV rays could penetrate the eye, burning a hole in the retina. It causes no pain, with people only becoming aware of the damage a few days later when two permanent black spots distort their vision.
For around two minutes the moon will mask the sun, causing darkness illuminated only by the corona - the outermost part of the sun's atmosphere which appears as a halo around the moon. However, even then it is unsafe to look as infrared radiation is present.
Children, whose eyes are less developed than adults, are most at risk.
A spokeswoman for the Royal College of Optometrists said eye specialists were "praying for rain on the day". She said: "People just don't realise what a huge danger this is. It will undoubtedly be devastating for hundreds, if not thousands."
Those who think wearing sunglasses will protect them could actually suffer more harm as the shades cause the eye's pupil to dilate, leaving it even more exposed to harmful rays.
Ms Mullen is sceptical of the value of solar glasses, thousands of which will be given away on
the day. She said: "They are flimsy, cardboard one-size-fits-all things."
Ms Mullen's charity is most concerned by the large numbers of nursery and primary schools planning trips to Cornwall.
She said: "When you've got 30 or so small children, one of them is going to manage to turn around and look at the vital moment. My advice to anyone with small children is put them indoors, close the curtains and watch it on TV."