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    Re: Emergency sun declination
    From: Fred Hebard
    Date: 2004 May 21, 17:09 -0400

    A graphical method of computing the sine of a function.  Sine is
    opposite over the hypotenuse. #3 =opposite, #4=hypotenuse.  Then dec =
    22.5*sine(days past vernal equanox), etc for other seasons.
    On May 20, 2004, at 4:48 PM, Royer, Doug wrote:
    > What Jim has shown in his emergency dec. post has been taught in
    > lifeboat or
    > emergency navigation courses for sometime.It is accurate enough for
    > use in
    > these circumstances to warrant knowing how to accomplish it.It is a
    > straight
    > forward procedure.But you must have a rose or universal plotting
    > sheet.This
    > is something most likely to be had in a lifeboat or ditchbag.
    > Between each cardinal point there will lay roughly 90 days/points.Try
    > to
    > evenly section off in 1/3rds or less groups of days.Within the
    > sectioned off
    > group for the date in question guestimate the location for that date's
    > point
    > on the arc.
    > 1.Take a parrallel rule and from the horizontal axis,makeing sure it
    > stays
    > parrallel with that axis,move the rule up to the date's point on the
    > arc.
    > 2.Draw a line from that point to the vertical axis.
    > 3.Measure the distance from the line thus drawn to the point where the
    > vertical and horizontal axis's meet in the center of the rose.
    > 4.Measure the distance from the center of the rose to the edge of the
    > arc.
    > 5.Divide the "date measurement"(#3) by the total radius
    > measurement(#4)to
    > get the ratio of the two.
    > 6.Multiply that ratio by 22.50*(degree)
    > This will give you a working dec. of the sun enough to reduce a sight
    > or
    > series to establish some deceant idea of where you are in an emergency
    > situation.
    > Ken's meathod appears to be along the same lines,though I've never
    > seen it
    > before.
    > Hope this answered your question.
    > Thanks for taking the first stab Ken. I too am not sure that I
    > understand
    > what Jim but was ashamed to admit it.
    > Jim, do you have a diagram to illustrate your method?
    > Ken, I am going to take a stab at yours. Sounds interesting.
    > Robert
    >>> 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.
    >> I am not sure I understand what Jim is saying, but here is what I have
    > been
    >> preaching for many years.  I would very much appreciate someone
    >> telling me
    >> if I am wrong, and if so, how much wrong!
    >> I tell people to take a piece of paper and draw horizontal lines, each
    >> separated by an equal amount.  Label them +30, +20,+10,0,-10,-20,-30.
    > Draw
    >> a circle centered on the 0 line so that the top of the circle is on
    >> 23.5,
    >> and the bottom is on -23.5. Label the cardinal points June 21, Sept
    >> 23,
    > Dec
    >> 22, and March 21.  Then I tell them to fill in the dates around the
    >> circle
    >> (easier said than done), and read the declination directly.
    >> I am guessing that if the Earth were in a circular orbit around the
    >> sun
    >> instead of elliptical, then my analogue would be OK. Does the
    >> ellipticity
    > of
    >> the orbit make this wrong?
    >> Ken Gebhart

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