What’s so special about the sunlight during an eclipse? Isn’t it the same old sunlight we see the rest of the time?
Yes, it is, but because the event is so interesting to look at, and because the normally blinding solar disk is partly blocked out, the temptation is to look, and look, and look. See “Chemistry explains why you shouldn’t stare at the solar eclipse without proper protection” (C&ENews, print 21 Aug 2017, online 14 Aug 2017).
The article explains the photochemical events that trigger retinal damage (the “heat” of the sunlight is not to blame) and it describes several options for safe viewing of the Sun. Here’s a bit from the article:
The Greek philosopher Socrates is said to have told Plato in 399 B.C., “People may injure their bodily eye by observing and gazing on the sun during an eclipse.”
Despite the age-old wisdom, in the days after these dazzling events, doctors still report cases of blurry vision or even blind spots caused by peering at the sun. The injuries incurred are actually the same as when people stare at the sun on a normal day; the difference is people are particularly tempted to look up during an eclipse.
Normally, glancing at the sun isn’t much more than a “nuisance,” says Dirk van Norren, a retired professor of ophthalmic physics at the University Medical Center Utrecht. “But if you glance over an hour or so, it adds up,” he says. “That’s the whole danger of an eclipse.”
Van Norren estimates that it takes about 20 or 30 glances, adding up to approximately half a minute of staring, before an adult would get injured. Though skipping the proper precautions is a bad idea, most eclipse-related injuries are minor, he says, “because frankly, you’d have to be quite an idiot to stare so long into the sun.”
Chem 201 students should be able to assign E and Z labels (or say why this is impossible) for each C=C group in 11-cis-retinal and all-trans-retinal (see figure in article).