I remember in elementary school, a big deal was made of not looking directly at a solar eclipse. A very big deal. Even a quick, unprotected glimpse could cause blindness. At the time, it didn't make sense to me - why would looking at an eclipse be any worse than looking at an uneclipsed sun? Was the seemingly heightened paranoia because it's an event that people are likely to want to look at? Or is there something else about an eclipse that warrants the extra attention? Even NASA acknowledges that eclipse warnings may be a bit hyperbolic:
In the days and weeks preceding a solar eclipse, there are often news stories and announcements in the media, warning about the dangers of looking at the eclipse. Unfortunately, despite the good intentions behind these messages, they frequently contain misinformation, and may be designed to scare people from seeing the eclipse at all.The fact of the matter is yes, you can do serious damage to your eyesight looking directly at a partial solar eclipse. During the period of total eclipse - when the moon completely obscures the sun - it's safe to observe with the naked eye (see also NASA link above). However, this isn't without risk since the shadow will continue to pass and without proper timing you could find yourself looking directly at a partial eclipse. Even when 99% of the sun is obscured, the remaining 1% is intense enough to cause serious retinal damage.
Is looking at a partially-eclipsed sun more hazardous than an unobscured sun? In a way, yes. Because even a mostly blocked sun can be damaging and the surrounding illumination in these conditions can actually be quite dim. In this case the eyes natural defense - constriction of the pupil - doesn't kick in right away. The pupil is exposed to the sun in a dilated state, allowing more of the damaging light to enter the eye. (Of course an unobscured sun will be sending that much more light to your eye, so this isn't a proper comparison.)
The bottom line is that there's nothing magical about a solar eclipse, and nothing special about the light it gives off, but after every eclipse there's a spike in cases of retinal injury and eyesight damage. Take proper precautions when viewing an eclipse and don't stare directly at the sun - eclipsed or not.
[Image source: Wikipedia]