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: A simple question, I hope, on almanac SHA
    From: Frank Reed
    Date: 2013 Apr 12, 10:27 -0700

    Hi Stan,

    I was giving someone else a hard-time recently about non-descriptive subjects, so I've modified this subject to provide just a hint of what your question was about. I hope you don't mind! :)

    You wrote:
    "The SHA of stars changes very slowly, so the Nautical Almanac uses a single value for the three days of a daily page. I would have to believe that this is the value for 1200 UT of the middle day (rounded to 0.1'), but I have not been able to find this, or something contrary, documented anywhere."

    I would guess you're right, too. I was having dinner here on the island last night with Herbert Prinz (delicious seafood at Jamestown Fish), and a text message came in during dessert with your message so I offered it up for discussion. We spent hours talking about navigation and astronomy and NavList, so SHA trivia fit right in! We agreed that your suggestion is almost certainly correct. HP also pointed out that, of course, this is documented somewhere in technical publications on the Nautical Almanac, but good luck digging it up. I suggested that you could determine this by re-calculation. Find as many cases as you can where the SHA changes by 0.1 minutes from one page to the next. Then find some source that calculates SHA's for every hour (my site does) and as long as they're using nearly identical input data and nearly identical precession and nutation models, you should be able to find cases where the SHA flips its tenths digit on just the right date. Here's the link for my web-based software that does this: http://reednavigation.com/lunars/nadata_v5.html. Other NavList members, including Paul Hirose, have similar tools available.

    -FER


    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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