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: Alexandre Eremenko
    Date: 2005 Feb 13, 02:39 -0500

    On Sat, 12 Feb 2005, Frank Reed wrote:
    > Interesting. I don't know anything about this.
    > What can a typical trained
    > marksman achieve in terms of angular accuracy?
    0.4'-.5' without telescopic sights (See also Jared's message).
    unlike Jared, I see some analogy between star shooting
    and target shooting. In both cases, not only sharpness
    of your eye but also firmness of your hand is relevant.
    As I understand, a marksman does not really see the central circle
    on the target s/he intends to hit. She only sees the larger circle,
    but with some training she is able to aim at its center
    with better accuracy than her eye resolution.
    Something similar probably happens when an experienced observer
    determines the touch of two discs as you described.
    > know if there are any people who have
    > genetically superior foveas  in their
    > eyes with the cones more tighly packed
    According to my mother (an ophtalmologist), the density
    of those cone packing does not vary much among people,
    and 1' is the theoretical limit derived from this density.
    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). The
    reasons why some people
    have such resolution is not known. Or at least was not known
    30 years ago when my mother told me this.
    By the way the well-known double star (Mizar, zeta of Big Diper)
    was used to test the vision of ancient Arab warriors.
    The distance is 12', so this was not a very rigorous test:-)

    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