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    Re: Moon Lower Limb Ex-Meridian Back Sight (reduction solution)
    From: Greg Rudzinski
    Date: 2012 Jul 19, 09:06 -0700

    1. Apply dip and index correction to back sight (hs) Moon lower limb.


    115* 11.9' (hs)
    -2.7' dip
    0 I.C.
    115* 9.2' (ha) back sight lower limb


    2. 180* - 115* 9.2' = 64* 50.8' Moon upper limb (ha)


    3. 64* 50.8'
    - 0.5' refraction
    -15.0' semi diameter upper limb
    +23.0' parallax HP 55

    64* 58.3' (Ho)

    4. 64* 58.3'
    -8* 52.0' N. Declination
    + 27.5' ex-meridian correction

    56* 33.8'

    5. 90* - 56* 33.8' = 33* 26.2' N. Latitude

    For ex-meridian correction
    (a)=3.9 (t)=20.6

    (a)(t^2)/60
    (3.9)(20.6)(20.6)/60 = 27.6' added


    The ex-meridian Moon back sight reduction is a convoluted affair which explains why most CN practitioners avoid this observation.

    Greg Rudzinski


    [NavList] Moon Lower Limb Ex-Meridian Back Sight
    From: Greg Rudzinski
    Date: 14 Jul 2012 15:16
    Here is an ex-meridian back sight taken through a light haze to a sharp horizon while on an island mooring. What cove am I moored at ? This observation was extremely difficult even while on a mooring. Finding the Moon required observing the Moon to a short horizon then setting the sextant to 180 - the sextant reading. Even then getting the Moon into the field of view had me twisting about with my back to the Moon.

    7/10/2012
    UT 13:40:50
    Hs 115* 11.9' Lower Limb (back sight)
    Height of Eye 8 ft.
    Index Corr. 0.0'
    (a) =3.9
    (a)(t^2)/60 = added XM correction

    Semi Diameter 15.0'
    HP 55.0'
    Declination 8* 52.0' N
    GHA 123* 39.6'
    LHA 5* 9.7'
    Time After Meridian Passage 20.6 minutes


    Greg Rudzinski



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