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    Re: Venus transit June 8 and sextants
    From: Robert Eno
    Date: 2004 May 12, 14:28 +0100

    Thank you Frank,
    
    A few good points to be sure. I can tell you this though: there is
    absolutely no danger of any ham-handed neighbour of mine ever getting
    hold of my precious sextant. I twitch uncontrollably even when an expert
    handles it and feel a great sense of relief when it is finally handed
    back to me.
    
    God!  I am shuddering already.
    
    But a follow-up question: another poster (not sure if it was you Fred)
    indicated that he brings the sun down to the horizon to view it; the
    implied message being that it is safer. My question is, why is it any
    safer to look at the sun's image by bringing it down to horizon level
    than it is by setting the sextant at 0 and looking at it directly
    (notwithstanding a decreased chance of neck strain). You are still
    observing a very bright object; albeit one reflected to another location
    by the index mirror. Even at that, you would still be blinded if the
    shades suddenly fell out of line.
    
    Robert
    
    
    
    
    
    
    >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
    >
    >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
    > ------------------- Email sent using AnyEmail (http://netbula.com/anyemail/) Netbula LLC is not responsible for the content of this email

       
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