Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Position from altitude and azimuth.
    From: Bill Lionheart
    Date: 2020 May 20, 07:18 +0100
    Just to be clear I concluded that an isoazimuthal curve is not a small circle although it can be close. It has a variable curvature and non zero torsion. 

    Moreover the angle subtended by a chord at the circumference of a circle on a sphere is not constant. 


    On Wed, 20 May 2020, 02:32 David Pike, <NoReply_DavidPike@fer3.com> wrote:

    Bill Lionheart you wrote: So the discussion Frank and I were having off list is how how to turn this in to a proof that the isoazimuth is a small circle. 

    I’ve been thinking about this and I’ve come to the conclusion that it’s important here to decide whether we mean ISO Z and ISO Azimuth.  E.g. consider Dec 30N and azimuth 060.   Z can flip at GHA + 180 ,  such that Z is still 60, but azimuth is now 360 – 60, so you’ll get a ring which might or might not be a perfect circle.  If you stick with ISO Azimuth.  Your saying the direction of the star is always at 60 degrees to the meridian, so in this particular case you’d get a spiral.  DaveP  

    View and reply to this message

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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