Lyle Aldridge
Senior Member
As it relates to the naked eye, this is discussed to some extent in the Chou article linked to Russ's (RustierOne's) second post above. He says "thermal injury of the retina is normally not possible unless the pupil is well dilated or unless the solar disk is viewed through binoculars or a telescope (White et al. 1971, Sliney and Wolbarsht 1980)."(Emphasis in original).
He goes on to state, though, that [naked eye] staring at the sun poses a photo-chemical hazard, rather than thermal. Fortunately we humans have an involuntary response that usually prevents us from being able to do that. We close our eyelids and/or look away, usually in less than a second, before an injury can occur. There is always the risk. I'd guess, that some one of us is a freak of nature, so testing your own response is a bad idea.
One way we can overcome the reflex reaction - but definitely should not - is to stare at the sun through a tiny pinhole, as I did when viewing a partial eclipse when I was about 8 years old. DON'T!! That morning in the schoolyard, I felt no pain whatsoever, nor any other symptom of the harm I was doing. My injury was the photo-chemical type, not a thermal burn. But it was ultimately life-altering, when it showed up a decade later during an academy entrance physical, and put an early end to my dream of becoming a naval aviator and astronaut.
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I believe the eclipse was the annular on April 30, 1957. From where I was growing up in Washington State, there was only something like 20% occlusion. The pinhole I used was poked with a sharp pencil in a piece of construction paper.
