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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Shadow sights for longitude
    From: Brad Morris
    Date: 2018 Jan 13, 15:05 -0500
    Hello Geoffrey 

    I found your description quite compelling and read it several times over to be assured that I properly understood it.  Would you mind confirming my understanding? 

    1) Two stars have the same celestial longitude.
    2) we have a vertical line and a vertical slit, separated by a few meters 
    3) when the stars are observed and they are not on our meridian, only one or the other will be blocked by our equipment referenced in (2).  Why?  The azimuth of the objects are dissimilar when not on our meridian.
    4)  as the earth rotates, the vertical slit is moved, keeping one of the two stars occluded.  The delta azimuth diminishes as the meridian transit nears.
    5)  eventually, both stars are on our meridian and the delta azimuth becomes momentarily zero.  We can then use that as our reference to project other lines on the ground.

    Do I have that right?

    Questions:
    a) two points define a line, consequently, there will be pairs of stars which coincidentally will align vertically when not on the prime meridian.  How did the Egyptians know which two stars had the the same SHA and therefore which pair to use?  
    b)  You mentioned that the referenced stars are circumpolar.  This would mean that they would align twice a day, unlike other random pairings. Is this how the star pair was selected?
    c) How did you keep the vertical slit vertical?  Or from rotating in the slightest of breezes?

    Thanks in advance!

    Brad



       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID 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