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
    Re: Index Error
    From: Robert Eno
    Date: 2004 May 5, 11:01 +0100

    Interesting concept. I am still trying to wrap my mind around it to see
    if there are any flaws. It appears to make sense to me.
    Nevertheless, the question remains, how does one apply the rest of the
    correction. One text suggests "applying the correction until the sextant
    can be adjusted" but does not tell the reader 1.) how this difference is
    to be applied and 2) what adjustments must be made to the sextant.
    Every time I reach a point where I think I have it all figured out
    another glitch appears to take the wind out of my sails.
    P.S. I should mention that backlash is not a factor here: it is my
    practice to rotate the verier drum in the same direction; always. Even
    the finest sextants have a bit of backlash.
    >I don't think you should be performing this step:
    > 62.6 - 0.7 = 61.9
    >You observed two diameters.  Let's correct each of them
    >separately for the derived index error:
    >  32.0 - 0.7 = 31.3
    >  30.6 + 0.7 = 31.3
    >Therefore your measurements say twice the diameter is 62.6,
    >which is the same as you get by simply adding the two raw
    >observations together.
    >Thus, your measured semidiameter is 15.65 -- a bit closer,
    >but still not exact.
    >If you measure the SD to be too small, it could be explained
    >by flattening due to refraction.  Basically, the altitude of
    >the lower limb is less than the altitude of the upper limb,
    >so their refraction corrections would be different.  But the
    >difference should be no more than 0.05' for reasonable altitudes.
    >If you measure the SD to be too large, it could be explained
    >by the illusion that brighter objects appear larger -- is this
    >called illumination?
    >        -- Bill
    Email sent using AnyEmail (http://netbula.com/anyemail/)
    Netbula LLC is not responsible for the content of this email

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting 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