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: Additional error found in H.O. 249
    From: Gary LaPook
    Date: 2009 Oct 8, 01:17 -0700

    Wouldn't one obtain the SHA
    and declination of a star from the Nautical Almanac for the day in
    question?
    Why would it be preferable to obtain
    this from HO 249 other than convenience?
    
    Sure if you have the current N.A. or the Air Almanac or
    Geoffrey Kolbe's excelent long term almanac.
    
    But if you use the epoch 2010 data from volume 1 and apply precession
    and nutation you do not need any other books. Unfortunately the volume
    2 and 3 almanac positions are unusable since the precession and
    nutation tables do not cover this long period of time.
    
    
    gl
    On Oct 7, 2:13�pm,  wrote:
    > Quote:-
    > "I do understand that stars have proper motion."
    >
    > They do, but even the fastest moving have completely negligable proper 
    motion and are difficult to measure with the most sophisticated photographic 
    methods over long periods of time.
    >
    > Precession and nutation are the main reasons for apparent star motions, 
    simply speaking measured by and referenced to the changes of the first point 
    of Aries around the equinoctial and the obliquity.
    > The changes are only slight, with a period of 25800 thousand years for full 
    precession around the equinoctial; �with �nutation having �much shorter 
    period linked to the motion of the Moon of 18.6 years but the effects are 
    miniscule: in the order of longitude by 17" and obliquity by 9".
    >
    > Douglas Denny.
    > Chichester. England.
    >
    > ==============
    > Original Message:-
    >
    > Hi Gary
    >
    > What is the magnitude of these errors? �Several arc-seconds? An arc-minute? �
    > Several arc-minutes? A degree?!!?!?!?
    >
    > My 1853 Bowditch gives a long term almanac, in which the motion or rate for
    > the stars is given for a year, and you just multiply by years and add to the
    > base value. �Surprise, it agrees quite
    > readily with current values (not perfectly, but dang close). �It didn't seem
    > like a huge delta for a 156 year run (1853 -> 2009). �I can't imagine this
    > to be a huge injected error for 1982 -> 2009.
    >
    > �Wouldn't one obtain the SHA
    > and declination of a star from the Nautical Almanac for the day in question? �
    > Why would it be preferable to obtain
    > this from HO 249 other than convenience?
    >
    > Best Regards
    > Brad
    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList+unsubscribe@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