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: Luni-Solar Distance
    From: Paul Hirose
    Date: 2010 Oct 28, 15:17 -0700

    George Huxtable wrote:
    > And I still wonder about the use of Frank's lunar-distance calculator, at-
    > http://www.historicalatlas.com/lunars/lunars_v4.html , to solve the 
    > converse problem from that it was intended for.  I would be grateful for 
    > any step-by-step guidance on how to go about using that calculator to 
    > establish the GMT at the moment of a lunar distance observation, from an 
    > unknown longitude, without observing the altitudes. 
    > Here is the example I asked about, once again-
    > "A navigator is somewhere on the Equator, at
    > lat = 0º, and knows it from his previous observations. We know (though he
    > doesn't) that at midnight, 00:00 hrs at the start of 26 March 2005, he is
    > exactly on the Greenwich meridian, at long = 0º, at which moment he takes a
    > precise lunar distance between the Moon's near limb (it's full Moon, so
    > either limb will do) and Regulus, of 36º 48.9'.
    > However, not knowing his exact longitude, he guesses it to be 01º 00' 
    > East."
    If longitude is unknown, I think the solution for time is indeterminate.
    My lunar program confirms George's distance to Regulus, and says the 
    value is increasing .31' per minute of time. Then I moved the assumed 
    position 1° east. This decreased lunar distance by .93'. In this case, 
    one degree of longitude east has the same effect as 3 minutes of time 
    So, if we move 5 degrees east and observe 15 minutes later, the two
    effects should cancel. Let's see. After I make those changes to the
    input data, my program says the lunar distance is 36°48.81'. Close!
    Moving the observation 17 seconds later makes it perfect. That is,
    George's lunar distance is observed from 0°N 0°E at midnight, and also 
    from 0°N 5°E at 00:15:17 UTC. There are an infinite number of such time 
    / longitude pairs. Without some additional constraint, there's no way to 
    know which one is correct.
    I filter out messages with attachments or HTML.

    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