Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Navigation without Leap Seconds
    From: Bill Noyce
    Date: 2008 Apr 18, 15:54 -0400

    Leap seconds correct for variations (mostly the slowing down) in the
    rate of the Earth's rotation.  I think everything else that's an input
    to the Nautical Almanac tabulations -- the Earth's orbit around the
    sun, and also the other planets, the Moon's orbit around the earth,
    proper motion of the stars, etc. -- is computed from the free-running
    time that ignores leap seconds.  In a way, we're still clinging to the
    pardigm used in the Almanac's early days, when things were tabulated
    by Greenwich Apparent Time.  Fortunately for navigation, and for
    Geoffrey's long-term almanac, most celestial objects don't move very
    much in a few seconds.  Thus, for practical navigation, it doesn't
    matter whether we use UTC or the free-running clock for their
    positions.  It *does* matter when we go to translate those positions
    into GHA.
    To answer the question that started the thread, I think future
    navigators will compute a position, then adjust their longitude.  That
    uses (marginally) better positions for the celestial objects than the
    alternative, which would apply a sort of "equation of time" before
    looking up positions.
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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