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: Latitude and longitude around noon
    From: Robin Stuart
    Date: 2017 Mar 29, 04:35 -0700

    Lars,

           You asked: “Can you really extract those fifteen seconds of time from the raw data given by Frank, without knowing the longitude à priori? Aren't you pulling more information out of the data than that data contain?”

    Expanding on what Frank responded; The 15 seconds is not pulled from the data. It’s the known offset between the time of peak altitude and Local Apparent Noon (LAN) which is common to all observers at the given latitude and dos not depend on longitude. Another question to ask might be “can a fit to the data locate the time of the peak altitude to within 15 seconds?” to which I feel pretty confident that the answer is yes.

    You can retrace my own voyage of discovery on the need for this correction if you follow the thread starting here. Antoine “Kermit” Couëtte gave an expression for the offset in plain text

    " ΔT culmination-transit (s) = 48/π * (tan Lat - tan Dec) * ( d/dt Lat ['/hour] - d/dt Dec ['/hour] ) "

    here and original paper that derives it in full is here.

    In his original formulation of the problem Frank reminds us of the need for this correction when he states “Incidentally, my "northing" speed was zero, but the Sun is northbound at about 1 knot this time of year.”

    Regards,

    Robin

       
    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