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Ahha,

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.

Fred

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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