Solar eclipse

[Nitin Nigam]

Hi All,
I want to know about how a partial solar eclipse can damage eyesight. As far as i know total eclipse is dangerous because when sun is completely covered, it become near darkness (and if you are watching it now, the pupil of your eye will be wide open), and the moment sun come out from behind it suddenly becomes bright suddenly(And your pupil will not be able to shrink fast enough, allowing a lot of light falling on your ratina, causing harm to the eyes)

So i know total eclipse is harmful, but can partial eclipse be harmful in the similar way or any other way?

P.S. Please don't say that harmful radiations come to earth when sun is hidden.... if that was the case we would not go out in the night also.

[Nickolas Case]

If my memory serves me, it is the partial eclipse you can't look at. If you think about it, a partial eclipse puts out a lot more light than the fraction of the sun that escapes pre and post full eclipse. Any full eclipse I have ever witnessed hasn't been SO dark that one couldn't plainly see.

A cool trick (learned in elementary) is to take two pieces of white paper, poke a hole in the center of one and hold the second about 8-10 inches behind the first.

Happy star gazing!

[Mandar Khire]

I don't know about how a partial solar eclipse can damage eyesight!
or i am also not follows cool tricks as Nickolas Case told us.

I want to say the easiest & safer way to see any eclipse is,
you should look it on television (follow the rules of television viewing to protect eyes from television, other wise television also damage eyesight).

Don't be superstitious like this or like that way.
[ August 02, 2008: Message edited by: Mandar Khire ]

[Mike Simmons]

This guy (a professor of optometry published by NASA) says that the period of totality is perfectly safe to view, but the partial eclipses before and after are indeed dangerous. I think the problem is that our irises open wider because there's less total light in the field of view, so it seems safe - but the intensity of light at particular points on the iris (the parts where the visible sun is imaged) is as high as ever. Also, normally we don't have any reason to stare at the sun for prolonged periods, but with an eclipse, something interesting is happening, so temptation is higher. And the damage is painless and not apparent for several hours, so people have no feedback telling them there's a problem.
[ August 02, 2008: Message edited by: Mike Simmons ]

[Nitin Nigam]

Originally posted by Nickolas Case:
If my memory serves me, it is the partial eclipse you can't look at. If you think about it, a partial eclipse puts out a lot more light than the fraction of the sun that escapes pre and post full eclipse. Any full eclipse I have ever witnessed hasn't been SO dark that one couldn't plainly see.

A cool trick (learned in elementary) is to take two pieces of white paper, poke a hole in the center of one and hold the second about 8-10 inches behind the first.

Happy star gazing!

Fraction of sun will still give lesser light the full sun. We occasionally look at the full sun and that is not harmful (If we pass the glance, not stare). How come a partially eclipsed sun (which is less bright)be harmful?

[Mike Simmons]

I believe I just answered that. The total amount of light is less, but the intensity at any one spot on your retina is the same as it is for the full sun. The iris expands because it detects less total light, but the parts of your retina where the sun's image appears are still burned. The nerves controlling the iris respond to the total brightness they detect across the whole eye, not the brightness at a single point (or small region). So they don't recognize the danger.

[Nitin Nigam]

Originally posted by Mike Simmons:
The nerves controlling the iris respond to the total brightness they detect across the whole eye, not the brightness at a single point (or small region). So they don't recognize the danger.

Hmmm... this seems reasonable.
Thanks Mike.