Even when most of the Sun is hidden by the Moon, the remaining light can permanently damage your eyesight.
Looking directly at the Sun can burn the light-sensitive retina at the back of the eye, causing a condition known as solar retinopathy.
Worryingly, the retina has no pain receptors, so you may not realise that damage is occurring. Symptoms, including blurred vision, blind spots, distorted sight and changes in colour perception, may not become apparent until several hours later.
Use genuine eclipse glasses
If you want to look directly at an eclipse, use proper solar-viewing glasses or a purpose-made handheld solar viewer. These should comply with the recognised ISO 12312-2 international safety standard.
Buy them from a reputable optician, astronomy supplier or established retailer. Check the glasses carefully before use and discard them if the filters are scratched, torn, punctured, wrinkled or separating from the frame.
Ordinary sunglasses are not suitable, regardless of how dark or expensive they may be. Welding masks, smoked glass, exposed photographic film, CDs, DVDs and sweet wrappers are also unsafe.
Put your eclipse glasses on before looking towards the Sun. When you have finished viewing, turn away from the Sun before removing them. Children should be closely supervised throughout.
Never combine eclipse glasses with optical equipment
Do not look through binoculars, a telescope or a camera while wearing eclipse glasses. These instruments concentrate the Sun’s rays and can cause severe eye injuries while also damaging the viewing glasses.
Cameras, telescopes and binoculars need professionally manufactured solar filters fitted securely over the front of their lenses. If you are uncertain about the equipment, consult an experienced astronomer or attend an organised public viewing event.
You should also avoid pointing your smartphone directly at the Sun for prolonged periods. This can damage its camera sensor. Holding a phone between your face and the Sun does not provide reliable eye protection.
Try indirect viewing
One of the safest ways to enjoy an eclipse is through projection. A simple pinhole projector can be made using two pieces of white card. Make a small hole in one card, stand with your back to the Sun and allow the sunlight to pass through the hole onto the second card.
The projected image will show the Moon gradually moving across the Sun. Never look through the pinhole itself.
A kitchen colander provides another easy method. Hold it so that sunlight passes through its holes and projects onto the ground or a sheet of white paper. Each hole will create a tiny image of the eclipsed Sun.
Watching a reputable live television or internet broadcast is the safest option of all, particularly for young children or anyone who cannot obtain genuine solar-viewing glasses.
What if you accidentally look at the Sun?
Seek urgent medical advice if you experience blurred or distorted vision, a dark or empty area in the centre of your sight, unusual sensitivity to light or changes in colour vision after watching an eclipse. Do not assume the problem will simply disappear.
An eclipse should be a memorable experience for all the right reasons. A little preparation—and the correct viewing equipment, will allow the whole family to enjoy it without putting their eyesight at risk.
Guidance is available from Moorfields Eye Hospital, the Royal Astronomical Society and NASA’s eclipse safety service.
https://www.ras.ac.uk/news-and-press/news/how-see-best-solar-eclipse-visible-uk-1999?utm_
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