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
    Lunars in the Nautical Almanacs in 1919 and later
    From: Frank Reed
    Date: 2005 Apr 16, 21:56 EDT

    The predicted lunar distance tables were dropped  from the British Nautical
    Almanacs in 1907 and from the American Nautical  Almanacs in 1912. But
    instructions on computing and using them were included for  quite a while after those
    dates in appendices to the almanacs.
    The  "American Nautical Almanac" included an appendix through 1933 that
    explained how  to calculate a lunar distance if a navigator chose to use them. It
    gave two  simple methods for calculating the distance, one that gave the cosine
    of the  distance which was appropriate for large angles and the other that
    produced the  sine of the distance which was good for small angles. The appendix
    was updated  with fresh examples every year. There was no advice on clearing
    a measured lunar  in the American almanac.
    The British "Nautical Almanac Abridged for the  Use of Seamen" included an
    appendix through 1919 or 1924 or perhaps 1928  (haven't found out for sure yet
    and secondary sources disagree) that explained  how to calculate a predicted
    lunar distance using versines, haversines, or log  haversines. But this appendix
    went much further than the one in the American  almanac. It also included
    good, basic instructions on the general principle of a  lunar distance and
    described the calculations necessary to clear a lunar using a  method closely
    related to Airy's excellent method. This appendix suggested  shooting lunars with
    the Sun, the bright planets, the usual nine lunars stars,  and also Castor,
    Betelgeuse, and Procyon as good options for lunar  distances.
    So why were they keeping this up so many decades after lunars  had fallen
    into practical disuse? In short, for the same reasons we think about  doing
    lunars today. The introduction to the appendix in the British Abridged  Nautical
    Almanac says it perfectly: "there is probably no better method of  becoming an
    expert observer with the sextant than by practising this  observation".

    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