What happens when we stare at the sun? --- Kiran, Tirupati, India
If you have read the article on how suntans and sunburns work, you know that the sun can kill skin cells. The UV rays in sunlight cause irreparable damage and the cells die. Fortunately for the skin, cell death is not catastrophic because the dermis is fairly thick. New skin cells replace the damaged cells, and after a week or two the skin is good as new.
Unfortunately for your eyes, there isn't a way to replace damaged cells in the retina like there is in the skin. So when someone stares at the sun, the cells in the retina die. And they they are dead for good. So a blind spot forms, or general blindness can occur in especially bad cases.
The moral of the story: Never look directly at the sun. Or at the arc of a welding machine or arc lamp.