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: Working a lunar - a PS
    From: Brad Morris
    Date: 2009 Aug 6, 16:34 -0400

    Hi Hanno

     

    I have been considering your statement “If I see things right, there must be a LOP which connects all those locations on Earth that have a given, fixed difference DT between the meridian passages of sun and moon” 

     

    Just to be sure I understand your statement, I will re-write it.  The first object crosses your meridian. Let us assume that it is the sun.  While this is LAN, we don’t care about that, you merely start your timepiece stopwatch.  Next we wait for the second object to cross your meridian.  When it does, you stop your timepiece.  We observe the delta time.  From this one data point, we are expecting a LOP.

     

    This has nothing to do with the altitudes of the objects, just the Delta Time of the meridian crossing.

     

    One problem (not insurmountable) is that the two celestial objects have apparent diameters.  As such, we must perform a few more measurements.  That is, assuming you are using an older theodolite with 5 wires, you would record the 5 times that the leading limb crosses each wire and the 5 times that the trailing limb crosses each wire, and then mathematically determine when the object was on your meridian.

     

    The next problem (not insurmountable) is to align the theodolite to your meridian. Even Bowditch in the 1800’s knew how to do this.  However, the requirement to align the theodolite to the meridian precludes any use of this method whilst at sea.

     

    Now which LOP corresponds to the Delta Time (DT)?  I suggest to you that it is your MERIDIAN.  Anyone, at any other latitude, that is on your longitude will measure the same precise value that you do.  Now there’s an interesting outcome!  Sure, the altitudes will be different, but the DT will be the same. 

     

    Can we tell which meridian?  Considering that the moon essentially travels it’s diameter in an hour, we run right into the resolution problem, very similar to the Lunar lack of resolution.   Since we will be measuring with a theodolite, we will have a very good measurement for the time of meridian crossings, assuming that the theodolite is aligned to the meridian to perfection.   Assuming you measure precisely and accurately, then the answer is yes.

     

    Best Regards

    Brad

     

     



    "Confidentiality and Privilege Notice
    The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you."

    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@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