Boy, lotsa stuff here.
They don’t get around to teaching you this stuff in optics class, I tell you.
1.) Continuously looking at the sun in one spot is Not A Good Idea. You don’t fry your retina (that would require oil), but you can heat it up considerably. The energy density is pretty high, and continued looking will cause damage. See the last entry in the Bad Astronomer’s message board Here, where a practicingg optometrist who’s seen this says that less than 2 minutes’ exposure wil probably cause damage:
http://www.bautforum.com/archive/index.php/t-2419.html
2.) The sun is about 93 million miles away, which is, for reasonable calculations, infinitely distant. minor7’s point doesn’t really apply – the sun’s image is less than a gnat’s whisker away from the actual focal point.
3.) One of the great things (usually) about the eye is the way that, unlike a flat photographic plate or a flat CCD, we have a sensitive surface that can form into a curved shape. Our eyes can therefore conform to the shape needed to get a good fiocused image everywhere (and which also allows the eyeballs to rotate in the sockets. A pretty neat design), so you can’t take refuge in the “the sun’s not in focus away fro m the center” argument – the sun is in focus off-axis. If it weren’t, your peripheral vision would be pretty useless.
4.) The retina is more tightly packed near the center of vision, in the part called the fovea (as already noted), which is the most sensitive for vision, and where we do most of our seeing. I’ve never heard or reasd anything about its relative sensitivity to pain. I’d suspect it was higher, but have nothing to back that up. Damage to the fovea has bigger consequences than damage to other parts of the retina, however, for obvious reasons.
5.) my suspicion is that damage to the other parts of the retina are just as possible with prolonged looking as at the fovea if you continue to look at the same place. But you probabnly aren’t. Your eye moves around , and the sun’s image is probably not striking the same part of your non-fovea retina all the time. If you’re looking right at the sun, you’re keeping the image about in the same place. If you’re not, there’s a heckuva lot of area that not the fovea it can be hitting. Even if you think you’re looking in the same place, I’ll bet you aren’t – your eyes can shift their gaze, and you can move your head as well. The sun’s image is probably moving around on the inside of your eyeball, rather than hitting the same spot repeatedly.
6.) Your eye has a couple of defenses against excessive intensity, in addition to shifting gaze. Your pupil will close down to restrict the amount of incoming light. Not only does this reduce the overall amount of light coming in, but having a smaller pupil also increases the size of the image on your retina (for a small and distant source. Otherwise, it still spreads out the light somewhat for a larger object), thereby decreasing the intensity (photon flux per unit area). In the second place, people squint, which also closes down the effective aperture even more, further restricting the light coming in and making the image larger.