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    October Lunar
    From: Jeremy C
    Date: 2008 Oct 3, 08:42 -0700

        The sky cleared last night (October 2, 2008) for a bit, and a  waxing
    crescent moon along with Venus appeared low in the Western sky just
    after sunset.  It wasn�t an ideal situation for a lunar, but offered a
    chance to shoot one amidst the overcast days that have plagued me for
    the past week or so.  Position is Lat 41deg 14.7�N , Long 075deg
        I checked the index error and found 0.9� on the arc and then
    proceeded to shoot 10 near-limb lunar distances.  Without a horizon, I
    was stuck with calculating altitudes of both Venus and the Moon.
    Temperature is 50 degrees, but pressure is unrecorded.
        I have recently acquired Celestaire�s new version of the 7x35 scope,
    and it was my first time to use it on my sextant.  (Thank you Ken for
    the opportunity to get one before I leave for sea next week).  The
    extra magnification certainly helped in shooting the lunars, as was
    the steady shooting platform and low altitudes of both bodies.
        Admittedly, this was a poor time to shoot lunars.  Both bodies were
    well below 10 degrees of altitude, and the observed lunar distances
    were just below 12 degrees, which does not usually help with accuracy,
    but I wanted to practice, so I proceeded.
        The observed Lunar Distances were as follows:
    LDs                          Time (UTC)
    11deg 56.2  23h 13m 58s
    11deg 56.8  23h 14m 50s
    11deg 56.8  23h 15m 21s
    11deg 57.1  23h 15m 48s
    11deg 57.3  23h 16m 18s
    11deg 57.1  23h 16m 52s
    11deg 57.3  23h 17m 31s
    11deg 57.6  23h 18m 00s
    11deg 57.8  23h 18m 28s
    11deg 57.8  23h 19m 00s
    Using Frank�s calculator for the reductions, I found an average error
    of 1.11� with the outside errors being 1.3� and 0.9�.  Averaging the
    times and distances, I also got an error of 1.1�.  Since all of the
    sights seem to have a good �grouping� ie accurate, the error in
    precision is the real question.  Is it strange refraction due to low
    altitudes?  Perhaps is an error in my sextant calibration, or perhaps
    just a personal observation error.  I will have to shoot some more to
    see where the data point to.
    Navigation List archive: www.fer3.com/arc
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