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: determination of longitude and the prime vertical
    From: Frank Reed CT
    Date: 2007 Apr 15, 04:15 EDT
    George H, you wrote:
    "If Polaris is indeed that far out, can any predictions from that site be
    trusted, for precise work? I wonder if others have comments about that."
    That was one of the reasons I put together my own online Nautical Almanac (at the address below). You may recall that this is not the first time problems have cropped up in the star data on that site. A couple of years ago, you helped Omar Reis fix the problem with proper motion (of all the stars), which, in fact, he had not included at all. For historical analysis, this was a very big problem. I can't tell what's wrong with his Polaris position, but yes, it's wrong. It seems to be a pattern: many software developers have built tools for calculating the positions of celestial bodies for navigation. They usually get the planets and Sun and Moon right. But they frequently have problems with the navigational stars. I suppose this is because the testing procedure is very different. For stars you have to look at very small errors accumulating over years, and you have too look at the positions during different seasons of the year. With the planets, using any of a variety of methods, once you have it right for every January 1st for five years in a row, you're probably all set. Because of the way Solar System positions evolve, it's just not very likely that an error could emerge that would not show up on those five test dates.
     
    -FER
    42.0N 87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars




    See what's free at AOL.com.

    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to 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