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: Digital Camera Celestial Navigation
    From: Paul Hirose
    Date: 2008 Jul 06, 21:12 -0700

    Marcel Tschudin wrote:
    > Why not measuring the sun's horizontal diameter? This measure is
    > (almost?) not affected by refraction.
    
    I discovered the "almost" a few days ago, when programming a function to
    compute refracted semidiameter. The values at the 12 and 6 o'clock
    position angles (in the horizontal frame) were exactly what I expected
    for a Sun-sized object, but at 3 and 9 o'clock they were about .2" too
    small.
    
    After some debugging, I realized there was nothing wrong with my code.
    Refraction reduces the semidiameter in every direction. When the left
    and right limbs refract up, they move on great circles which converge at
    the zenith. With a body of 16' semidiameter, and sea level refraction,
    this decreases the semidiameter about .27". I tested this at several
    altitudes from 10 degrees to 80, and it didn't vary more than .01".
    
    In this case, the algorithm was smarter than its designer.
    
    Later I remembered that Jean Meeus ("Astronomical Algorithms", chapter
    on refraction) says the Sun's horizontal diameter is reduced slightly by
    refraction. His figure (credited to Danjon) is .6", practically
    independent of altitude.
    
    --
    I block messages that contain attachments or HTML.
    
    --~--~---------~--~----~------------~-------~--~----~
    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