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: Pub. 249 and the spherical earth
    From: Roger W. Sinnott
    Date: 2017 Dec 20, 19:29 -0500

    There is one area of sextant navigation where the Earth's ellipsoidal shape has an effect:  lunar distances.  The "clearing" process is supposed to move the measured Moon-star angle from what it is at the Earth's surface to what it would be at its center.  But all the standard corrections just move it to where the observer's vertical line, extended downward, intersects the Earth's rotational axis -- NOT the geocenter.

     

    Chauvenet talks about this in his Manual of Spherical and Practical Astronomy (Vol. 1, page 397, of the 1891 edition reprinted by Dover).  In his fully worked example for an observation made at latitude 35 N, the final adjustment to the geocenter alters the lunar distance by another 4.7 arcseconds.  It appears this correction could grow two or three times larger for sights made in high latitudes.

     

    Roger

     

     

       
    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