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    Re: Venus transit June 8 and sextants
    From: Fred Hebard
    Date: 2004 May 12, 09:29 -0400

    What's the problem with the shades that go over the eyepiece of the
    telescope overheating and blowing up?  They were a fixture of sextants
    for years and still are in some models.  Is there a history of this
    occurring or is this speculation?  A piece of glass blew into the
    cornea of my left eye and it was no fun.  Maybe the light from a
    telescope could burn a hole in your retina, but lacerating your cornea
    could be even more damaging to your eyesight.
    On May 12, 2004, at 6:17 AM, Frank Reed wrote:
    > Robert E asked:
    >  "Why is this dangerous?  Is it because there is a possibility of the
    > shades
    >  slipping out of position?"
    >  In a way, yes.
    >  Fundamentally, it is dangerous because there is a telescope in the
    > light path. This is intrinsically dangerous when you're looking at the
    > Sun. If you carry this risk alone, then there's no problem. But do
    > you??
    >  Imagine yourself out on a street corner with your sextant on June
    > 8th. You know what you're doing; nothing could go wrong. And you say
    > to yourself, 'I know what I'm doing... nothing could go wrong..."   So
    > you demo your sextant to your neighbor who happens to have heard about
    > the transit of Venus today and is enthusiastic to see the show. And
    > you're pleased to show the show... You swing the shades one way.. you
    > swing them back... you demo the sight... You hand the sextant to your
    > neighbor and before you've noticed he swings the shades out and looks
    > straight through at the Sun. He jumps away quickly but it's too late.
    > He's got a blindspot. He has permanent damage to his eye. And you've
    > got a legal and moral nightmare.
    >  That's a parable, of course, but the fundamental concept stands; it's
    > error-correction. So what do you do? How do you avoid the potential
    > for a minor error with major consequences when you're casually using a
    > sextant to observe the Sun?
    >  Frank R
    >  [ ] Mystic, Connecticut
    >  [X] Chicago, Illinois

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