Why is it dangerous to look at a solar eclipse?

Looking directly at the photosphere of the sun (the bright disk of the sun itself), even for just a few seconds, can cause permanent damage to the retina of the eye, because of the intense visible and ultraviolet rays that the photosphere emits. This damage can result in permanent impairment of vision, up to and including blindness. The retina has no sensitivity to pain, and the effects of retinal damage may not appear for hours, so there is no warning that injury is occurring.

Under normal conditions, the sun is so bright that it is difficult to stare at it directly, so there is no tendency to look at it in a way that might damage the eye. During a total eclipse, however, with the sun covered, it is easier and more tempting to stare at it. Unfortunately, looking at the sun during an eclipse is dangerous even if totality occurs only briefly. Viewing the sun’s disk through sunglasses or any kind of optical aid (binoculars, a telescope, or even an optical camera viewfinder) is extremely hazardous. The best methods are to use special solar filters, welder’s glasses, or a pin-hole camera.


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