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From: palmer@cit-vax.Caltech.Edu (David Palmer)
Newsgroups: sci.astro
Subject: Re: Sunset Eclipse?
Message-ID: <1058@cit-vax.Caltech.Edu>
Date: Sun, 19-Oct-86 17:59:55 EDT
Article-I.D.: cit-vax.1058
Posted: Sun Oct 19 17:59:55 1986
Date-Received: Tue, 21-Oct-86 22:09:47 EDT
References: <649@nike.UUCP> <696@cadomin.UUCP>
Reply-To: palmer@cit-vax.UUCP (David Palmer)
Distribution: world
Organization: California Institute of Technology
Lines: 36

Organization : California Institute of Technology

    The danger of looking at a partially eclipsed sun is much greater than
that of looking at an uneclipsed sun.

	When the sun is partially eclipsed, it produces less light (obviously)
which makes your surroundings darker.  To compensate, your eyes open up from
an iris diameter of about 1mm to a diameter of about 7mm, a fifty-fold
increase.

	Then, when you look at the sun, the image you see has a much greater
intensity (light per unit area on the retina) than it would have if your eyes
were stopped down and you looked at an uneclipsed sun.  (The iris has adjusted
so that the same total amount of light comes through, but since the area
producing that light has been decreased, the intensity has increased.)

	This high intensity light can damage the retina much more quickly
than an ordinary glance at the sun can.

	Another point, someone mentioned that they had used two slides made
from unexposed film as a sun filter.  I have heard that THIS IS A VERY BAD IDEA.
Apparently, color film, when exposed and developed, only blocks out the
visible light, letting IR and UV through.  Probably the same is true of
exposed and developed color slide film.  You should only use exposed and 
developed black and white film, which apparently, does not have this problem,
although it may have others.  (Use at least two layers, and, just in case,
only use one eye.  Monocular vision is better than none)


			David Palmer
			palmer@cit-vax.edu
			...seismo!cit-vax!palmer

	I've followed you, talked to your neighbours, tapped your phone,
	and even shot at you to see how you would react.  From my observations
	I have come to one irrefutable conclusion: You are Paranoid.