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
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: Understanding a 1902 Sumner
    From: David C
    Date: 2017 Jan 20, 22:44 -0800

    Sorry if I was oblique with my refrence to EOT but looking at a modern table for March the EOT is negative.  Look at the data form - Cor. Eq. T  5 13.3 + A.T.  It seems to me that it shows M.T.G. = EOT + A.T.  So to get apperent time :

    A.T. = M.T.G. - EOT

    I saw the  + AT reference but was not sure if the "+" meant add to AT to get MT or the opposite. I tried both and  subtracting  gave me a sensible answer.

    Here are my results

    GPS   41° 17.57' S    174°  47.36' E

    CoP app    41° 17.3' S   174°   48.0' E

    Blackburne's Sumner    41° 18' 30" S  174° 46' 27"

    These numbers tell me three things:

    • The observations were accurate to <0.3'. This is to be expected given that they were taken on land by an experienced Extra Master who was Nautical Adviser to the NZ Government and also Examiner of Masters and Mates.
    • There were errors in Blackburne's reduction method. This was acknowledged by Blackburne.
    • The concept of a datum is meaningless when comparing observed  positions.

    Thanks to John and Frank for pointing me in the correct direction. I plan to follow the links and download the 1902 NA. Then I can work the timesights from scratch using the sin2 1/2t  (hav) formula and tables.

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID 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