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    Re: Getting to know a sextant.
    From: Tony Oz
    Date: 2017 Feb 25, 13:24 -0800

    Hello!

    As we've get a nice four-day-long holiday till next Monday, so I'm taking my sextant to the Finnish Gulf shore to practice a bit. Still no scope, only the ghost ring attached.

    After the index mirror adjustment and horizon mirror tuning-in - I guess only the excentrisity error remains.

    I found a book from 1976 on the navigator's equipment handling and adjustments. Among other things it explains how to calibrate a sextant by star-star measurements. This particular topic was already discussed here some time ago.

    Here's what that book says on the topic:

    • to measure the six certain angles, star-Polaris;
    • properly clear the data;
    • compare with the given table.

    The suggested stars are (see p-045):

    • Kocab;
    • Alioth;
    • Capella;
    • Vega;
    • Alpheratz;
    • Altair.

    One can easily calculate the current angle values from the current NA.

    But the book goes on and gives the table (see p-290) with per-month star-Polaris angles. Some of those angles do change noticeably though the year.

    What is this? A parallax by Earth's orbiting the Sun, right?

    Since I'd like to make an estimation of the excentrisity in my sextant - where can I get the modern parallax data (per-month) of those stars?

    Please comment.

    Regards,

    Tony

       
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