Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Shadow sights for longitude
    From: David Fleming
    Date: 2018 Jan 13, 10:47 -0800

    I had not heard of shadow sharpeners but I believe you are right.  It seems that they are again a pinhole camera that allows you to image the edge of the shadow producer!


    I'm imagining that the precision of the length measurements remain constant.  That is, if the best I can do is 1 mm out of 10cm scale then if I make 
    a larger instrument that I'll be limited to the same precision or 1cm out of 1 meter, or...


    On Sat, Jan 13, 2018 at 7:23 AM, David Pike <NoReply_DavidPike@fer3.com> wrote:

    David Fleming wrote:  Increaseing shadow length will not improve the accuracy.  As has been noted the accuracy is limited by the sun not being a point source of light. 

    I think we’re talking about two different error sources here.  There’re the difficulties caused by the Sun not being a point source of light and also the difficulties in measuring the base and the perpendicular of our triangle accurately, even if the Sun was a point source.  Size won’t improve the former although it might make that difficulty more obvious, but it can improve the latter.  DaveP

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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