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: Basic celestial naviagtion using a scientific calculator
    From: John Karl
    Date: 2010 Aug 14, 18:52 -0700

    Gary,

    You remind me of another reason why I like the book "CN in the GPS Age".

    The azimuth angle A calculated with your equation, sin A = cos d sin LHA/cos H, requires the arc-sine which has two solutions for A between 0 and 180, leading to a complicated ambiguity.

    But the above book uses Cos A = (sin d - sin L sin H)/(cos L cos H), employing arc-cosine for A which has a unique solution for A between 0 and 180. Then the rule to get Zn from A is simple:
    if LHA is greater than 180, Zn = A
    If LHA is less than 180, Zn = 360 - A.

    Since the LHA is known exactly, there is no ambiguity -- just simplicity.

    It's true that the cosine equation is a bit more complicated than the sine equation, but since d, L , and H are stored in the three calculator memories, punching in two more trig functions is an excellent trade off for avoiding ambiguity (and for keeping the discussion simple for beginners). Also this lack of ambiguity is even more valuable for higher level programming.

    BTW, it's useful to distinguish between the azimuth and called "Z" in tables, and the azimuth angle called "A" used in the above equations. These are different angles as explained in the above book.

    --JK
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------

       
    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