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    Re: Oblateness correction
    From: George Huxtable
    Date: 2010 Nov 30, 20:36 -0000

    Lars wrote-
    From: "Lars Bergman" 
    Sent: Tuesday, November 30, 2010 5:42 PM
    Subject: [NavList] Oblateness correction
    In the Sight Reduction Procedure chapter in the Nautical Almanac, the
    correction for the oblateness of the earth, to be added to the Moon's
    parallax in altitude, is given (in degrees) as
    OB = -0.0032 (sin Lat)^2 cos H + 0.0032 sin (2 Lat) cos Z sin H
    where H is apparent altitude, Z true azimuth in the range 0 ... 360 and Lat
    is latitude in the range -90 ... 90. Now, in the second term the sine of
    two times latitude gets different signs depending on hemisphere. Shall it
    be like this, or ...?
    Lars, 59N 18E
    Lars is worried about apparent lack of symmetry of this correction, between
    Northern and Southern hemispheres.
    But if he takes two situations, in which the positions of the Moon and the
    observer have both been reflected about the equator, then the azimuth of
    the Moon, as seen by the observer, will be shifted into a different
    quadrant, reversing the sign of Cos Z, and thus undoing any asymmetry.
    Is that an answer?
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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