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    Re: Raw data for bubble
    From: Bill B
    Date: 2007 Mar 12, 20:53 -0500

    Gary wrote
    > Another point, for those learning celestial, I think it is usefull to
    > use the sextant correction tables from the Air Almanac rather than
    > those in the Nautical Almanac. In the N.A many of the corrections are
    > combined into one, e.g. refraction, semi-diameter and parallax in
    > altitude are all combined in the moon correction table. A learner will
    > not see the pattern or where the various items of the correction comes
    > from. Using the A. A. you have separate corrections for refraction
    > (for all bodies), dip (if using the natural horizon), semi-diameter
    > (if using the moon or the sun), and parallax in altitude (if shooting
    > the moon.) This can give you a better grasp on what is going on rather
    > than rote memorization of the process using the N. A. correction
    > tables.
    I have been trying to understand the components of the moon correction
    tables, and playing with the computational method preceding the concise
    reduction table in the N.A.  Below S = SD = semidiameter
    PA = HP cos H    = (S/.2724) cos H
    Ho = H - R + PA plus/minus S
    =  H - R + ((S/.2724) cos H) plus/minus S/.2724
    Gary mentioned refraction, semidiamter, and parallax.  The N.A. also has a
    formula to correct for oblateness. One of my texts mentions correction for
    augmentation of the moon (the change in apparent diameter due to change in
    distance for an observer on the face of the  earth vs. the center as the
    moon rises from the horizon to the zenith.
    To better understand the components, I have been deriving my own formulas
    for parallax and augmentation.  They are not elegant ;-)
    Here is where I get confused.  I can determine distance given the SD and
    radius of the Moon, I determine SD given if the distance and Moon's radius
    are known, etc.
    Thinking inside the box, that 0.2724d equates to 0d 16' 20.64", which if it
    is an SD, would put the moon 227,057 miles away (on the close side of its
    distance range) given a Moon diameter of 2159 miles.  HP is SD/0.2724, and S
    is derived by HP * 0.2724. It feels like a dog chasing its own tail.
    Without distance I can only derive distance by converting HP to SD which
    uses a constant from one set of circumstances.
    That said, four questions:
    1. Do the tables make any attempt (lacking Lat input) to account for
    2. Do the tables or PA plus/minus S compensate for augmentation? Is that
    perhaps built into the daily pages figures?
    3.  How the heck does one constant, 0.2724 and a simple expression (PA = HP
    cos H) get us even close?
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