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
    Name or NavList Code:
    Email:
       
    Reply
    Re: AP3270 Table 5
    From: David Pike
    Date: 2017 Mar 27, 06:29 -0700

    I said:  Yes, you can get + and – d.  When declination is the same name as the latitude, d appears in my complete edition of AP3270 Vol 3 to be positive.  One of our spherical trig experts will no doubt explain why that has to be so.
     

    Maybe it’s not that difficult to explain.  For the special case of the body’s LHA=0, the PZX spherical triangle becomes a straight line and the sign of d (in HO249/AP3270 Vols 2 and 3) can be easily seen from a 2-D diagram (Photo 1).  For other cases, perhaps a model is the best way of studying the problem.  Imagine a grapefruit pierced by three mapping pins, P, Z, and X, bounded by a rubber band.  P is the Pole, Z is the position of the observer, and X is the sub-stellar point of the celestial body.  The side ZX is the co-altitude of the body on the PZX spherical triangle, or 90-Hc.  As pin X is moved up or down equating to a change in decination, side ZX will stretch or contract.  If the rubber on side ZX stretches, co-alt is increasing, so Hc is decreasing and d is negative in sign and vice versa (photo 2).  My apologies to those in the Southern Hemisphere for putting north at the top.  Dave P



    File:



    File:



       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

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

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID 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