Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Emergency sun declination
    From: Doug Royer
    Date: 2004 May 20, 13:48 -0700

    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
    >
    >
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site