Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
    Re: False Horizons
    From: Nicolàs de Hilster
    Date: 2007 Nov 20, 20:10 +0100

    Isonomia wrote in 3932:
    > Eventually for my younger child  I tried setting up a plank in the
    > garden and tying the sextant up with  string to give a level, but the
    > darn sun moved so quick that it ran off the  end before I had a chance
    > to set it up with any accuracy. I'd appreciate any ideas!
    >   
    
    Then I proposed:
    >> Perhaps making a simple quadrant would do for the kids and instead of
    >> using two visors to look through you could make one with one small open
    >> visor and a larger closed one to cast the smaller visor's shadow onto
    >> the larger (so they do not have to look at the sun). After that exercise
    >> you can explain that a sextant does a similar job using two mirrors.
    >>
    >>     
    Which resulted in Isonomia asking me:
    > The principle sounds a good one for younger children and if the sun
    > ever shines, I'll try out what I think you mean to see how accurate it
    > is. But it would help if I understood what you meant by a "closed
    > visor".
    So I will try to explain here:
    
    Normally a quadrant is used in a forward manner, like you can see on 
    image 'using a quadrant.jpg'. Facing the sun with the naked eye is not 
    really commendable, so my proposition was to use the quadrant backwards. 
    For this we need a quadrant with an open visor ('A' in the other image) 
    and a closed visor ('B').
    
    For visor A you could take a screw eye, for B a piece of cardboard with 
    a cross drawn on it. Of course the line through the centre of the screw 
    eye and the intersection of the cross should be parallel with the 
    zero-line of the quadrant.
    
    Accuracy depends on the diameter of the quadrant, but it is known that 
    astrolabes could produce readings accurate as 20 arc minutes (radius 
    approximately 16cm).
    
    Nicolàs
    
    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

    File:


    File:


    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