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: John Karl's Celestial Navigation in the GPS Age
    From: Sean C
    Date: 2018 Apr 30, 16:45 -0700


    In my copy of 229 vol. 2, on the page for LHA 32° and Lat. 24° contrary name, the tabular values given for a declination of 18° are:

    Hc: 37°40.2'

    d: -47.6'

    Z: 140.5°

    The value of Hc must be adjusted for the 8.5 minutes of declination using the "d correction" and the interpolation tables. So, we turn to the interpolation table on the inside front cover. (The table in the front is for declination increments ranging from 0' to 31.9'. The table in the back is for increments ranging from 28' to 59.9'.) We look at the row for 8.5' of declination increments and the column for the tens part of the "d correction": 40'. There, we find a value of 5.7'. Next, we look at the nearest decimals row and units column for the rest of the correction: 7.6' and we find a value of 1.1'. We add this to the previous value of 5.7' to get a total correction of 6.8'. The "d correction" is negative, so we subtract 6.8' from the Hc of 37°40.2 to get 37°33.4'. (I'm not sure why John's value differs by 0.1', but this is trivial.)

    Now we must adjust the Z value according to the rules at the top or bottom of each opening of 229. Since our latitude is South, we use the rules at the bottom of the right hand page. And since the LHA (32°) is less than 180°, we must add the Z value to 180° to get the azimuth. 180° + 140.5° = 320.5°, which we can round to 321° if we like.

    If any of that was unclear, feel free to ask for clarification.


    Sean C.

    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