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: Problem: index correction by star
    From: Frank Reed
    Date: 2020 Oct 15, 11:53 -0700

    I would say that your problem is that you were taught (or have read) that you need to eliminate all "side error". That's the apparent left/right gap between the direct and reflected images. This is totally un-necessary. No error arises if there is a gap. The expression "side error" is a misnomer. Adjust your sextant leaving a left/right gap of, let's say, one minute of arc. Then you can place your star images side-by-side without much effort. This will yield good results if you can't try a tabletop approach (as below).

    I spent many years testing various methods for testing and reducing index error. The best that I have found requires a small "spotting scope" --a telescope with a magnification of 30-50x. Place your sextant on its side on a table looking at some suitably distant vertical "edge". Remove the standard scope. Mount the spotting scope on a small tripod so that it is aligned with the usual light path that the standard scope would see. You may want to place a temporary paper or cardboard baffle around the horizon glass so that you can guarantee you are only seeing the scene through the normal sextant view. With a magnification around 40x, ever tiny tenth of a minute of arc adjustment is directly visible, and you can repeatably and reliably assess (or better yet, zero out) your index error. With a good metal sextant, this adjustment or assessment will probably last for a whole observing season, possibly even for years.

    Frank Reed

       
    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