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: Eqn. of time
    From: John Cole
    Date: 2007 Jan 10, 18:01 -0800

    FrankReedCT---.com wrote:
    
    > And let's not forget
    > _http://www.analemma.com/_ (http://www.analemma.com/) .
    > It's a detailed site on all aspects of the analemma and the equation of
    > time, and also one of the oldest amateur web sites on the Internet with really
    > good graphic content on a technical subject. It dates back to the late 20th
    > century (!).
    >
    
    Thanks, Frank, for the reference.  A great site, very well done.
    
    Now, perhaps the historians and/or old timers can help with the
    following.
    
    My first exposure to celestial navigation was many years ago as an
    undergraduate in applied mathematics. Navigation at sea was disposed of
    in perhaps one lecture during a semester course on spherical astronomy
    taught by dons who generally looked down on anything of practical use
    and certainly never showed us how to use an almanac.
    
    We were taught that right ascension was tabulated and converted to GHA
    knowing Greenwich Sidereal Time (GHA Aries):
    
    GHAMS (Mean Sun) + RAMS = GST (GHA Aries).
    GHA star + RA star = GST
    
    When I became interested in practical celestial navigation forty years
    later right ascension had disappeared from the scene and GMT had almost
    disappeared as well.
    
    In some old texts I have noted excerpts from almanacs where for the sun
    two quantities R and E were tabulated (together with declination) as a
    function of GMT where R was defined as RAMS + 12h
    and E was defined as 12h - ET (Equation of Time). So GHAS = GMT + E.
    
    Thus during the period from the early 1900s sun data in the nautical
    almanacs seem to have evolved from tabulations of RA, through
    tabulations of R and E, to today's tabulations of GHA (or SHA in the
    case of stars).
    
    I assume the almanacs have always been subject to fads in the schools
    including fads in notation, academic astronomers versus practical
    navigators, competition among publishers of almanacs for sales based on
    improved ease of use, politics, and so forth. Can anyone share with us
    the history of this evolution?
    
    John Cole
    
    
    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    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