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
    Name or NavList Code:
    Re: Sextant accuracy (was : Plumb-line horizon vs. geocentric horizon)
    From: Frank Reed CT
    Date: 2005 Feb 16, 14:05 EST
    Alex, you wrote earlier:
    "However there are well documented cases of much higher resolution.
    (One person tested in XIX century had resolution of 1",
    but this seems to be the world record. Several people were described
    who could see the phases of Venus with naked eye)."
    I mentioned before that I was skeptical, and it only dawned on me while I was throwing out last week's back-of-the-envelope calculations that one arc-second resolution is literally impossible. The diffraction limit is imposed by the laws of physics and gives a lower limit of 15 arcseconds under the very best of circumstances (under typical circumstances, this optical limit is about 30"). If Nature chose to pack more cone cells into our foveas than one for every 15" of angle across the retina, they would not yield higher resolution.
    Can anyone think of a loophole I've missed here? The diffraction limit has some fuzziness of definition (there's a pun in there somewhere), but I don't think it's enough to help.
    42.0N 87.7W, or 41.4N 72.1W.
    Browse Files

    Drop Files


    What is NavList?

    Get a NavList ID Code

    (please, no nicknames or handles)
    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 Settings

    NavList ID 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