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: Lunars calculator
    From: Jim Thompson
    Date: 2005 Apr 2, 05:58 -0400

    I should let Frank or George explain this, but maybe if I take a stab then
    I'll learn too.
    The oblateness correction accounts for the distortion of the earth into an
    oblate spheroid (spinning ellipse) from a true sphere (spinning circle),
    caused by its spin around the polar axis.  As a result, parallax in altitude
    can vary by less than 20 seconds of arc between the spherical and oblate
    spheroid models.  This correcttion is not enough to worry about in most
    practical CN, even for lunar distance sight reduction.
    On page 280 of the Nautical Almanac (2004): "If an error of 0.2' is
    significant (then the) expression for the parallax in altitude for the Moon
    should include a small correction OB for the oblateness of the Earth...".
    On http://www.clockwk.com/lunars/easylun.html
    Frank wrote, "The method I've described here does not include a correction
    for the oblateness of the Earth. This can be added easily but it's a fairly
    minor issue."
    On http://www.i-DEADLINK-com/lists/navigation/0503/0048.html
    Alex quoted Frank, "Earth's oblateness yields a slightly non-vertical
    component to parallax..."
    On http://www.i-DEADLINK-com/lists/navigation/0210/0231.html
    Herbert Prinz wrote, "...correction for oblateness of the earth amounting to
    3" of arc..."
    Jim Thompson
    PLEASE NOTE NEW: jim3{at}jimthompson.net
    Outgoing email scanned by Norton Antivirus
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Bill
    > Sent: April 2, 2005 12:40 AM
    > Subject: Lunars calculator
    > Trying my hand at Lunars. In the results on the Frank/Centennia Software's
    > calculation screen, there is an angle given above "Corrected for
    > oblateness." I am unable to correlate that angle to anything I am aware of
    > at this point in my journey.
    > Any help in understanding its significance would be appreciated.
    > Thanks
    > Bill

    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