> > The theory is that you can't stand to look at the full sun long enough to damage your eyes. However, with part of the disc blocked by the moon, you can continue to look and the part that is still visible will burn your eyes. That's what they tell us.
>
> I had always heard it was something like since there was less light overall, your pupils would be more dilated thus letting the light from the disc (which is just as intense as always) do more damage. I have no idea how true that is.
>

I did an experiment once where I compared the ratio of UV light from the sun to the visible light. The measurements were taken 24 hours a day, 7 days a week, for about 2 weeks. If you looked at the data from the visible light detector (a photosomethingorother), you would watch as it gradually rose and then gradually declined, punctuated by drops every time a cloud passed in front of the sun. On the UV detector, it spent about a few minutes in the morning at sunrise getting up there, and then it _stayed_there_ the whole day, almost unchanged, until sunset, where it took a few minutes to drop all the way down. In other words, the clouds might block the visible light so you might not actually see the sun, but UV was still just as bright as ever.
If you want to know just how bright the UV from the sun actually is, there was one point where the ratio was 1:1... that was the last moment before sunset. At that point, the UV is just about to drop even though visible has dropped a lot already. Right then, the sun is just as bright in visible light as it is in UV, and that is just as bright as the UV is all day long. (UV shines right through clouds because, we supposed, the wavelength was much higher and didn't get "filtered out" by the couds).

I was sort of mulling this over one day, and also thinking about eye damage caused by the sun's UV, when I figured out a stupid trick. It was a very overcast day, and the sun was about to disappear. Using my peripheral vision, I tried to estimate about where the sun was going to be when the clouds covered it over. Closing my eyes, I had no after-image of the sun burned into my eyes. As soon as the sun disappeared completely, I just stared at the point where I last saw it (trying to track where it should be despite cloud movement). I stared for about a minute, then closed my eyes. Sure enough, there was a burned-in after-image of the sun in my eyes. The only thing I had been staring at were the thick, dark clouds, but the UV had still burned the sun's image into my eyes.
[Don't do this at home, unless it's Jan. 21]

-Enig"wish the photosomthingorother experiment took place during a solar eclipse"ma