How dangerous is it to watch a solar eclipse without proper dark glasses? I recall a Feynman story where he watched the first nuclear bomb test without eye protection, just through the window of a truck. Under the theory that normal glass filters most UV light.
Well, Feynman was one of the most brilliant scientists in history, but he was also quite insane. (As one of his students, I say this with a great deal of love and respect for him!) To answer your question, though, we need to distinguish between a partial eclipse and a total eclipse. You had best use eye protection for a partial eclipse, or even better, use a pinhole projector as I described elsewhere in this thread.…
But one must be careful. As soon as the moon stops blocking the sun, there are sun rays concentrated in a tiny point. Like looking at the point of a powerful laser, it doesn't feel as powerful as it actually is. Esp. regarding invisible wavelengths.