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: Cones of Position, Lunars and the Apollo Sextant
    From: Ed Popko
    Date: 2019 Aug 4, 05:42 -0700

    Frank,

    This explanation helps a lot. Now I know the apex of the cone is the center of the moon (cleared lunar), a point I missed when first trying to visualize this. And yes, a diagram would certainly help.

    I'm guessing here. I assume the body (star or planet) and the observer are somewhere on the surface of this very large cone, as it radiates out in 3D space from the moon. Yes?  

    Unlike traditional CelNav where the cone's centerline intersects the body's Ground Point on earth, the centerline of the lunar's cone will never pass through the earth. And because the stars are so far away when compared to the moon'd distance from earth, that centerline will always point from the moon more than 90 degrees away from earth. And if I still have this right, the Circle of Position formed where cone intersects the moon's surface, would only be partially visible from earth because part of that COP is over the moon's horizon. But none of moon's COP is particularly useful to us since we are not on the moon to make use of it.

    Returning to earth, it's easy to see that the cone's 'diameter' is so large that the portion of it's surface that passes through the earth is a plane of all practical purposes. And that plane's intersection on earth scribes a LOP, the observer is on that LOP.

    Is any of this right so far?

    Some questions:

    1. Does the cone's surface also pass through the center of the earth as well as the observer?

    2. How does our assumed position on earth relate to this Line of Position (cone intersection at a given UT)?

    Ed

       
    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