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: Basics of computing sunrise/sunset
    From: Douglas Denny
    Date: 2009 Jun 19, 02:17 -0700

    I disagree with you.
    
    Illuminance through an optical system depends on the relative sizes of 
    objective and exit apertures. Ignoring inefficiencies of the lenses, if all 
    the light entering passes through the exit aperture (and in properly designed 
    optical system it should) then the difference in intensity in/out is in the 
    ratio of the square of the diameters of the apertures.(ie their areas).
    
    If this was not so - explain please why it is that stars invisible to the 
    naked eye of aperture diam 6mm - because they are too faint (intensity too 
    low to stimulate the retinal cells),   become sudenly visible with a 
    telescope of aperture say, 100 mm diam?
    
    The answer is in the relative light gathering of the objective aperture being 
    bigger by far than that of the eye, and all that light becomes reduced to the 
    aperture of the eye through the exit pupil of the telscope.
    
    Douglas Denny.
    Chcihester. England.
    
    
    --~--~---------~--~----~------------~-------~--~----~
    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