How to watch without hurting your eyes
There is no moment during this eclipse when it is safe to look at the Sun with unprotected eyes. Not at maximum, not when it looks dim, not through cloud. The UK and Ireland see a partial eclipse only, so a bright sliver of the Sun’s surface is exposed the entire time.
What works
- Eclipse glasses certified to ISO 12312-2. They should carry that number printed on them. Check them against a bright lamp first: if you can see anything other than the lamp’s filament, or if they are scratched, torn or creased, throw them away.
- A pinhole projector. Free, and completely safe because you never look at the Sun at all. Make a small hole in a piece of card, stand with your back to the Sun, and let the light fall through the hole onto a second piece of card. You will see a crescent. A kitchen colander casts dozens at once.
- Shade under a leafy tree. The gaps between leaves work as pinholes. During a 90% eclipse the ground under a tree is covered in crescents. This is the easiest and most striking way to watch, and it costs nothing.
What does not work
- Sunglasses, however dark, and however many pairs you stack.
- Smoked glass, exposed photographic film, or a CD.
- Looking through a phone camera to compose a shot.
- A telescope, binoculars or a camera lens - even with eclipse glasses on. They concentrate the light and will burn through the filter and then through your eye. Those need a proper solar filter fitted over the front of the instrument.
Too late to order
Nothing posted now will arrive in time, and glasses bought in a hurry from a stall or a marketplace are the ones most likely to be counterfeit. Use the pinhole projector or the tree shade above - both are free, neither can be faked, and for a partial eclipse this deep the crescents scattered across the ground under a tree are the better sight anyway. If someone near you has spare certified glasses, check them against a bright lamp first.
The particular risk this time
This eclipse happens with the Sun low in the west, between about 2° and 23° above the horizon depending on where you are and when you look. A low Sun looks dim and feels comfortable to stare at, because the atmosphere is filtering out the glare. It is not filtering out the infrared and ultraviolet that actually damage your retina. A comfortable-looking Sun is exactly as dangerous as a blinding one, and retinal burns are painless - you would not know until hours later.
Children
Glasses slip off small faces. Pinhole projection or tree shade is the better option for young children, and it holds their attention longer anyway.