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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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