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    Re: Winter Sextant Sight Accuracy?
    From: Jared Sherman
    Date: 2002 Jan 10, 6:35 PM

    George-
     Latitude about 43N and tht puts a late afternoon sun around 11-12d above
    the horizon.
     I am aware of the possible errors, causes, and effects and did in fact run
    them all through a calculator to see just how far a change of 5F or 50mb or
    eye height would affect things, I have notes on exactly how far each can
    affect the readings.
     And I am aware of sextant index error which I think was the root
    problem--the index zero wheel may have loosened under my gloved hand, I will
    be checking this again and have since re-zero'd on a star which gives me a
    far tighter zero.
     The effect of taking a warm sextant out of the car does not exist, after an
    hour in my trunk near 35F the sextant is nicely prechilled thank you.
    
     The question remains: Has anyone found that it is harder to get absolute
    accuracy when shooting an afternoon sun from a lattitude 43N during the
    winter, when refraction causes the three factors of eye height, air
    temperature, and air pressue to be far greater in effect than they are for a
    typical summer sight from these same lattitudes?
    
     I also suspect that some mirage (from the ocean/air temperature difference)
    and a rough horizon (either thermal mirage or waves at sea) were involved. I
    wasn't getting a real crisp sight and I've gotten crisper before, I'm
    wondering if that air/water temp difference causes enough distrotion in the
    winter to make it something to routinely be mindful of.
    

       
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