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: The Star of Bethlehem and Navigation
    From: Frank Reed
    Date: 2009 Jan 2, 22:06 -0800

    Marcel, you know, this whole business is actually very closely related to the 
    issue of leap seconds. Fact is, we can predict (and retrodict) the positions 
    of the planets and Sun and Moon relative to one another with high accuracy 
    for many thousands of years in either direction, future or past. But the 
    orientation of the Earth is tougher, in part because we're asking for a fine 
    order of difference and also because dissipative forces are responsible for 
    the variations of the Earth's rotation. 
    
    While we worry about leap seconds once every year or two, if you want to work 
    the same problem 2,000 years backward in time, you need something like three 
    hours worth of leap seconds, give or take 500. In other words, we can specify 
    atomic time or ephemeris time without much ambiguity and calculate most 
    phenomena in the heavens, like occultations and eclipses, with great 
    accuracy. Their relative timings will be accurate. But we don't know the 
    exact local time when those events occurred as seen from the Earth since we 
    don't know exactly how much mean time differed from "true" time back then. 
    Was it 4:30 or 4:35 local apparent time? Right now, there's no way to know.
    
    -FER
    
    
    
    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.fer3.com/arc
    To post, email 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