What happens if you look at solar eclipse without safety glasses?

Any time you look at anything, a tiny image of it is focused onto the retina in the back of
your eye. If you had a tiny piece of film back there, you'd get a picture of whatever you're
looking at.

If the thing you're looking at also happens to be sending out heat in addition to light, then the
heat also gets focused onto the retina in the back of your eye. You're not aware of it, because
our eyes aren't tuned to respond to heat. But it's there.

That's why it's dangerous to look at the sun. It's a very intense source of heat, so at the same
time you're looking at it and forming a tiny image of it on the retina in the back of your eye, you're
also forming a tiny, very intense hot spot on your retina.

Have you ever used the sun and a magnifying glass to burn a piece of paper or cook an ant ?
That tiny hot spot is the same as the spot that appears inside your eye when you look at the sun.
If you leave it there long enough, you wind up with a small, permanent blind spot in your eye, right
there in the middle where you put the things that you want to see most clearly.

All of this is true any time the sun is up, and that includes the time during an eclipse. The thing
about an eclipse is that when strange things are happening with the sun, everybody is standing
there saying "Wow! Cool! Look at that! I've never seen anything like it. Everybody look at the sun!".
And then everybody else stops what they're doing and looks at the sun. So during a solar eclipse,
you have a lot of people who would never look at the sun, and they're staring at the sun.

That's what's dangerous about a solar eclipse.