The Sun is a star of light. It emits a radiance that dazzles us when we try to observe it directly. We instinctively close our eyes, which protects us. During an eclipse, that brightness is partially or totally reduced. We may think, for that reason, that we can look at the Sun at that time with no risk. But that isn’t true, and it can even cause irreparable damage to the eye.
The fact is, the Sun also releases invisible rays that reach us even when the Sun is partly blocked out. Those rays can be harmful for the eyes if we don’t adequately protect ourselves. Possible damage includes cataracts or macular degeneration with a resulting alteration of our vision.
During an eclipse, the most dangerous rays are the infrared ones. These can literally burn the retina and blind someone looking directly at the Sun at that moment. That burning is sneaky, because it doesn’t hurt. And just a few seconds are enough to cause permanent damage.
Safe watching of an eclipse is done by way of projection systems or by using filters especially designed to cut the harmful rays of the sun. The filter must be placed directly on the eyes, not on the telescope or the optical instrument. This prevents the harmful solar rays from getting through beside, under or above the filter.
Consult the professionals at the Planétarium Rio Tinto Alcan, your astronomy club or your eye care professional for more information on this subject.
Dr. Langis Michaud, optometrist, M.Sc. FAAO (Dipl)
Fellow - British Contact Lens Association (FBCLA)
Fellow - Scleral Lens Education Soc. (FSLS)
Fellow - European Academy of Optometry (FEAOO)
School of Optometry, Université de Montréal