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: 60° Pendulum Astrolabe
    From: Mark Coady
    Date: 2016 Jul 22, 06:04 -0700

    Geoffry,

    My knowledge of pendulum based astronomical devices is quite limited.  My question related to their accuracy is my understanding that a pendulum on the surface of the earth does not always point to the exact astronomical center of the earth.

    This pendulum "tilt" is related to the law of universal gravitation and the fact the earth lacks complete uniformity of mass.  It is both oblate and lumpy. The pendulum points to the gravitational center as affected by that location, and in places this may vary from the astronomical "center" or even the overall gravitational center by some value. 

    Such places in Bermuda I have seen noted as varying .25 miles in 15, measuring terrestrial distances vs using astronomical calculation.

    My curiosoty is how this pendulum issue might create an offset zenith and might affect a pendulum based device taking astronomical sights.  How does this device eliminate the error of astronomical vs. gravitational center.

    As the tilt apparently varies with local location, I would think it might throw off calculated positions vs WGS 84. 

    I say "I would think" because this particular device and issue is something I am only just learning about, so I could be "out in left field with snowshoes on" too..... 

       
    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