Staring at the sun will make you go blind.

Factual Questions
1

Because of the coming solar storm this weekend I have been reading admonitions not to do this in several articles about the solar flare. It occurs to me, however, that most people like myself can look at the sun for several seconds (possibly longer) at a time with no apparent ocular damage. Wouldn’t your eye simply close involuntarily some point due to the dis-comfort. How long do you have to look directly at the sun before eye damage is apparent?

2

It depends on a lot of things. The primary concern is burning of the retina, which can happen long before it feels uncomfortable. Especially at high noon, you should never look directly into the sun, even for less than a second, for this reason. The pupils can’t contract all the way shut, and your eyelids are controlled by (mostly) voluntary muscles, so you can severely hurt yourself.

3

You can view the sun safely with #13 or #14 welder’s glass or with those mylar eclipse glasses. Much more info about viewing the sun and how to avoid eye damage here:
http://www.skypub.com/sights/eclipses/solar/safety.html

4

Well Tralfaz, you can get permanent visual field cuts from retinal damage with less than 15 seconds of exposure. These individuals are generally out in strong sunlight, and they will forever see the afterimage of the sun in the center of their vision. Makes it a bitch for driving, and reading too. It doesn’t hurt, it just plays hell on the retina. Pain from bright light is due to the rapid constriction of the iris as it tries to cut down on the light entering, but if you’re already out in sunshine, looking at the sun won’t be painful, 'cuz your iris will be about as constricted as it can get.

Examining the retina in these patients is kinda neat, it looks like somebody had a grassfire right in the middle of a red-orange lawn, leaving a black burned space right over the macula, where the center of vision is.

5

Galileo studied sunspots by looking right at the sun, and eventyally spoiled his vision this way.
Only approach I can imagine is to do it with one eye and time how long it takes to permanently ruin that. Then, use your other eye, but not that long…