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: A noon fix inland with an peri-sextant
    From: Frank Reed
    Date: 2017 Dec 19, 14:13 -0800

    "The results were as shown in the photos below. The n-s error was 0.5nm and the e-w error was 1.4nm.  "

    Very nice! Did you try, or have you heard of, my trick for getting the exact time for the central line? Plot your sights on thin graph paper or even a transparency and then fold it in half, loosely at first. Hold it up to a light. The sights before noon and the sight after should overlap as narrowly as possible on one half-parabola. You slide the folded paper back and forth until they line up and then you make a hard fold. The crease now represents the axis of symmetry. Unfold and you can then read off the GMT. This is the best way I have found to do this manually --without a least squares fit in a spreadsheet or similar app, that is. Note: at sea almost always, and on land when not near the solstices (not a worry at this time of year), you have to correct this symmetry axis time for relative motion between the observer and the Sun. This is easy: either a simple table or a short calculation. But if we neglect this it can throw off the longitude by many miles.

    Frank Reed

       
    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