Why is looking at the sun during a solar eclipse worse than looking at the sun on a normal day?
The amount of UV radiation doesnt decrease substantially during a solar eclipse. The amount of visual radiation does though causing your eyes to dilate. The net result is that your eyes let in a lot more UV radiation than it would normally receive.
The sun is really, really bright. If you try to look directly at it, hopefully you have an impulse to look away. Even if you manage to suppress that impulse, you’re at least going to squint, shade your eyes, or do something to mitigate the damage.
During an eclipse, most of that brightness (in the visible spectrum, at least) is gone. Your eyes can open almost fully. That natural impulse to look away is much smaller and easier to suppress. You can look directly at it longer.
Longer exposure = increased chance of permanent damage.
The suns ability to damage your eyes is not usefully diminished by a total solar eclipse. While it doesn’t look bright enough to hurt your eyes, there’s still too much light and solar radiation by multiple levels for your eyes.
However, because the moon is blocking a lot of the light, it feels comfortable to look at. This means that you do not feel or see anything too bright from your perspective.
Which means that even though it feels fine, there’s still way too much damaging light getting in. Normally the sun is so bright that you’re naturally averse to looking at it. An eclipse is special because you don’t *feel* anything happening, but it’s still happening.
Imagine that you had a poison that tasted like cherries. It’ll kill you if you drink even a little of it, but normally you don’t because you can smell and taste the cherry flavor. Except you install a water filter and it filters out most of the poison but not all of it. Now you can’t taste it, but it’s still poisonous. It might take slightly more water to kill you, but it’s still there and horribly dangerous.
There’s also the fact that normally, the sun is boring, and a normal person wouldn’t be inclined to stare at it for long. “Ow! Crap! Yep, that was the sun, all right.”
During an eclipse, something *interesting* is going on up there, and people who otherwise know better than to stare at something painfully bright might find themselves “toughing it out” to see what’s going on.
That’s a bad idea.
It is bad looking at the sun during the day as well.
However during an eclipse it gets dark and your eyes open up to let more light in and then the “diamond ring” phase of the eclipse occurs and it gets very bright very quickly and can damage your eyes.