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: Luni-Solar Distance
    From: Douglas Denny
    Date: 2010 Oct 18, 14:59 -0700

    George wrote:
    "If the time was known, there would be no point in taking a lunar. That's
    the purpose of measuring a lunar-distance; to determine the time. So
    there's a bit of a paradox, in calculating altitudes with which to clear a
    lunar, for which time and position are both needed. To get round it, you
    have to assume a trial longitude first, and then use the lunar observation
    to refine that assumption".
    --------

    Exactly so. George has expanded on my terse meaning. He has said more accurately what I meant.

    I too have noted mention of using calculated altitudes to obtain time from a lunar distance if the altitudes were not obtained accurately (perhaps due to a hazy horizon?) and I wondered how they were to do that without a chronometer, when the whole purpose was to find time (and hence longitude) in the first place.

    It became apparent when it is suggested recalculating the altitudes with the found approximate calculated time, and then recalculating the lunar distance to give a new more accurate time - in other words an iteration process.

    The question is: does this converge? and how quickly. To save my going in to the maths to find out - does anyone know?

    Douglas Denny.
    Chichester. England.
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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