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: Longitude at noon
    From: Tracy Shrier
    Date: 2020 Sep 9, 14:58 -0700

    Hi Philippe,

    Are you are missing the difference between Mean sloar time and Apparent solar time? I know UT in the Air Almanac is Mean time. I recorded LAN with my watch referencing UT. Staying in the Almanac to reduce Long from GHA obviates the need for reconciling the difference. Does calculating Long from the time difference between Greenwich noon and LAN require the additional correction of the Sun's analemma - the 'equation of time'? Those on the NavList that know so much more can weigh in for us.

    Also of interest to me is the different GHA you derived: 111°28.2' vs my 111°27.9'. Not a big difference but is yours from the Nautical Almanac?   

    Lastly, in reviewing my work I see that I recorded the Sun's dec wrong, correctly using d = 5°40.2' gives me Lat 40°46.0' N, 0.6' off my GPS in my back yard!


    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