Why is staring at the sun bad?

Why do people tell kids not to look at the sun, when the body's natural reaction is to look away anyhow?

It is true that the human body naturally reacts to bright light. However, when staring at the sun, this is not always the case. It is especially dangerous during an eclipse because the illumination is less, reducing your tendancy to look away.

The most common injury to the eye from looking at the sun is a retinal burn. The retina has no pain recepters, so you will not realize that you are damaging your eye until it is too late. As a person stares at the sun, the sun's image on the retina is heating up and the retina may become severly burned.

Apparently kids are at the greatest risk for retinal damage(http://www.drgreene.com/21_169.html). Tell your kids to imagine what happens when they hold a magnifying glass up to a piece of paper. If it is held there too long, the paper gets burned. The lens of your eye is like a magnifying glass, and you don't want to burn your retina!

Warning, techno-babble: Unlike a light bulb, which is an extended source, the sun is acts like a point source, which means that the light will be more focused on your retina causing greater risk of damage. However, because the sun is a point source, you can easily "view" the sun, or a solar eclipse by using a pin-hole camera. One simple trick I used during a solar eclipse was to criss-cross my fingers between my hands and look at the shadow on the ground. I could see an image of the sun on the ground through every space between the shadows of my fingers.

Remember, the only safe time to stare at the sun is at night!