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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 
writes:
> 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@jimthompson.net
> www.jimthompson.net
> Outgoing mail scanned by Norton Antivirus
> -----------------------------------------
>

   

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