Can you really go blind by staring at the Sun?

6th April 2011

Asked by: STEVEN A COLLINS, BY EMAIL

It’s possible, but the hazard is often exaggerated. Even at midday, a normal eye will only let in enough light to heat the retina by about 4°C. You need at least 10°C to cause thermal damage. Looking at the Sun during an eclipse for more than a minute can cause damage, because your pupils are more dilated, but it doesn’t result in total blindness and isn’t usually permanent. If the Sun is within 10 minutes of setting below a sea-level horizon, the more dangerous short-wavelength light is absorbed by the atmosphere and it should be quite safe to look at the Sun.

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