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    Re: Emergency sun declination
    From: Henry Halboth
    Date: 2004 May 22, 16:19 -0400

    Determination of the Sun's declination lacking  a conventional tabulation
    thereof, whether approximate or accurate, is really a rather simple
    matter. Basic input requires that an understanding that .......
    The obliquity of the ecliptic = 23-26-30, or thereabouts
    The Sun's average daily motion in the ecliptic = 59'08" + is a measure of
    celestial longitude
    The ecliptic constitutes a great circle, as well as the hyp of a right
    spherical triangle
    Utilizing the foregoing, in the application of Napier's Rules,
    declination may be calculated by ...
    Sine declination = Sine 23-26-30 x Sine (59'08" x # days since equinox)
    The solution can be as accurate or approximate as circumstances may
    warrant. Accuracy will be increased as the following factors become known
    Date + time of Sun's entry into Aries or Libra, which varies per year
    Date + time of Sun's entry into Gemini + Taurus + Cancer, etc.
    True daily motion established by other means.
    Estimation of a table of natural sines can be produced in a myriad of
    ways, whether graphic, interpolative, or otherwise, and seems unnecessary
    of very much explanation. Regardless, if you have planned well enough to
    wind up in a lifeboat dry and equipped with sextant + dividers + penciis
    + plotting sheets + protractor + whatever + space to work + seasickness
    remedy to keep your workspace clean, you most probably will have a set of
    navigational tables as well, and maybe even a pocket GPS.
    By the way, I am surprised that mention has not been made of the traverse
    table in conjunction with the graphical methods mentioned, as further
    proposed but Dutton + others.
    On Wed, 19 May 2004 18:37:20 -0300 Jim Thompson 
    > What about this method for emergency calcuation of declination?
    > 1. Label a compass rose June 22 at 000o, Sept 23 at 090o, Dec 22 at
    > 180o and
    > March 21 at 270o.
    > 2. The radius on the vertical axis is the declination of the sun. A
    > horizontal line from any date around the circle intersects that
    > vertical
    > radius.
    > 3. Measure the length of the vertical axis from the center to the
    > intersection of the horizontal line, divide that length by the full
    > radius,
    > and multiply that ratio by 22.5o.
    > 4. Error is +/- 0.5o.
    > Jim Thompson
    > jim2{at}jimthompson.net
    > www.jimthompson.net
    > Outgoing mail scanned by Norton Antivirus
    > -----------------------------------------

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