Looking directly at the Sun, even during a partial eclipse, can cause serious, irreversible eye damage in seconds. That single sentence is the whole reason this article exists, and everything below follows from it.
The five rules, unchanged from the site’s own safety section
- Always use certified ISO 12312-2 eclipse glasses. That standard number is the only thing worth checking on the packaging.
- Check the glasses for scratches or punctures before using them. A damaged filter is not a slightly-worse filter — it’s an unfiltered one, in the exact spot the scratch is.
- Don’t use regular sunglasses, X-ray film, CDs or homemade filters. None of them block enough infrared and ultraviolet light, regardless of how dark they look.
- Inside the path of totality, it is only safe to look without protection during the exact seconds of totality — when the solar disc is completely hidden. Outside that window, or before and after those seconds, protection is mandatory at all times, with no exceptions.
- If you’re photographing the eclipse, your camera and telescope need their own dedicated solar filters, separate from your eye protection.
Why the “exact seconds” matter more here than in a typical eclipse
This is the one place where this specific eclipse changes the practical advice, not the rule itself. Totality is short and it varies sharply by city — from just 30 seconds in Bilbao to 108 seconds in Oviedo, with most towns somewhere in between (see our piece on the sunset eclipse for the full city-by-city breakdown). A 30-second safe window doesn’t leave room for hesitation: know in advance, from your own city’s timing, roughly when totality starts and ends, so you’re not still fumbling with your glasses when the one truly safe stretch of the whole evening opens and closes.
The rest of the event — every second before totality begins and every second after it ends, including the entire partial phase, which in several cities runs until the Sun sets — glasses stay on, full stop. There is no such thing as “it’s mostly covered now, it should be fine”: partial coverage of 50%, 90% or 99% is still bright enough to damage your retina exactly as fast as looking at the uneclipsed Sun.
The practical takeaway
Buy your glasses in advance from a reputable source, check the ISO 12312-2 marking and inspect them for damage the day of. Know your city’s exact totality window from the map above. Keep the glasses on for everything except that window, and put them back on the instant totality ends — not when you think it’s ended, but at the time you looked up beforehand.