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  • j_bertolottij_bertolotti@mathstodon.xyz
    Aug 5, 2026, 10:58 AM

    Health and Safety for the solar Eclipse

    On August 12 a large chunk of western Europe will experience a solar eclipse (here in the UK it won't be full, but 90-95% of the sun covered will be a beautiful spectacle anyway). Since I have read the most nonsensical advice on how to watch the eclipse (yes, this is the internet after all) let me try to help.

    First of all: why is looking at an eclipse dangerous for your eyes?
    The sun is BRIGHT. Our eyes evolved to see things using the small fraction of the sun's light that is scattered by a given object and reaches our eyes, which makes the sun painful to watch directly. Furthermore the sun is far away, which means that the rays of light arrive to us almost perfectly parallel to each other (if you want to be technical, the sun appears as a spatially coherent source), which means that the lens in our eyes will make an amazing job at focusing that light into a small spot on our retina. High brightness + small spot = your retina will burn and get scarred. Not fun.
    To make things worse, during the full eclipse there is a short time when the sun is fully obscured, and thus you don't need any protection to see the beautiful corona around it. But as soon as the moon move, the brightness skyrocket again and if you don't have any protection, it is "scarred retina" time.

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    #Eclipse #Eclipse2026 #Safety

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  • j_bertolottij_bertolotti@mathstodon.xyz
    Aug 5, 2026, 10:58 AM

    Thankfully it is not difficult to protect yourself. You need a filter that will let less that one part in a thousand to pass (do not bother with the exact number, just go with something CE certified). These are very cheap to produce, and since you are likely to need them for less than a hour, they are usually mounted on flimsy paper frames. As long as you don't break them, they are fine.
    What is NOT fine are sunglasses. They let way too much light through. Even worse, avoid binoculars&co like the plague.

    Another very safe option is what is called a pinhole camera. Take an opaque screen (I have successfully used cereal boxes before), make a small hole in it, and let the sun shine through it. Beyond (in the shadow of the screen) you will see a very crisp image of the sun, which is very safe to watch.
    If you want to be romantic (and you live in a place that allows you to do it), you can sit below a tree with a well-developed canopy. The small spaces between the leaves will each behave like a pinhole camera, and you will get tens or hundreds images of the eclipse on the grass. Very pretty ;-)

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