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    Re: Table A4 + elevation?
    From: George Huxtable
    Date: 2003 May 3, 22:08 +0100

    Marc Bernstein said-
    >The sight reduction tables for air navigation do have refraction tables. The
    >altitudes are listed in 5000' increments up to 55,000' and there is a
    >correction table for non-standard temperatures that goes from +47 to -95 C!
    >For 2100' and 20C, a little interpolation shows you need to subtract about
    >1.5' from Hs
    I don't understand this. What is Hs, in this context?
    The amount of refraction from a celestial body varies VERY greatly with its
    angular altitude in the sky, and so does the additional correction for
    height-and-temperature. Marc quotes an interpolated correction of about
    1.5', without specifying any angle for the incoming light. Such a large
    correction could only apply to a very small apparent angle, of the order of
    a couple of degrees, that is, a body just above the horizon, way below what
    any self-respecting navigator would choose to observe.
    Can Marc explain further, please?
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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