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: Lunars using Bennett
    From: Frank Reed
    Date: 2008 Jul 04, 04:45 -0400

    George H, you wrote:
    "The Sun's contribution to correcting the lunar, mainly the effect of
    refraction, is small, especially when the Sun is high. The Moon's
    contribution, mainly its parallax, is much greater. and more dependent on
    its altitude. Perhaps, then, a precise value for Sun altitude isn't really
    needed, and it can be estimated instead. I haven't quite convinced myself of
    the validity of that argument, and offer it up, for what it's worth, for
    someone else to knock down."
    
    Happy to oblige. In fact, it turns out that what you've said here is
    backwards. The Moon's altitude is generally LESS important than the Sun's
    (at the same altitude). The allowable error in the Moon's altitude is
     err_h_moon = (6')*tan(LD)/cos(h_moon)
    which permits some remarkably large errors in the Moon's altitude, while the
    allowable error in the Sun's or other body's altitude is
     err_h_sun = (6')*sin(LD)/cos(h_sun).
    These formulae are somewhat modified by refraction especially for altitudes
    below 20 degrees, but the qualitative behavior does not change. These
    allowable errors refer to errors in the clearing process of 0.1 minutes or
    smaller. If we also use the Sun's altitude for local time, then any error
    there would apply directly (and that's an easy one to understand; assuming
    the Sun is near the prime vertical, an error of a minute of arc in the Sun's
    altitude yields an error of one minute of longitude, just as in modern LOP
    navigation).
    
     -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