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: Time sight primer
    From: David C
    Date: 2020 Oct 10, 19:41 -0700

    In old textbooks there is a big emphasis on the times equations. Without having studied them in detail and learned them by rote they can be confusing. Here is an example.

    A week or so ago I took some PM sights and the next day some AM sights. I decided to work a sight from each day as a time sight, reduce them with Martelli which I was studying, and plot  the  LOP using the two point Sumner. I would use a plane chart. Easy I though. I could start a thread called "mix and match"  - at each point in the process I could chose a different path. For no particular reason I worked the PM sight first. The LOP looked sensible and passed close to my GNSS position.

    When I worked the AM sight things turned to custard. The resulting longitude did not make sense. I finally realised that the culprit was

    ATS = HATS + 12

    ATS  Apparant time at ship     HATS hour angle true sun.

    Martelli gives the ATS and  uses AM/PM notation. In the afternoon the "PM" takes care of the 12 hour factor.  Conversion from ATS to t is a simple matter of using the time to arc table in Norie.  However in the forenoon "AM" does not include 12 so the simple table lookup does not work.

    I hope that makes sense. I had just resolved the matter when I read Frank's post but will not know for certain until that I am correct until  I plot the second LOP and confirm that it passes near my GNSS position

       
    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