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: Averaging lunars: was Lunars with SNO-T
    From: Herbert Prinz
    Date: 2004 Nov 1, 05:52 -0500

    George Huxtable wrote:
    > It may be interesting to read what Tobias Mayer had to say on this topic,
    > [...]
    Thanks to George Huxtable for posting and Steven Wepster for translating. While
    we are at it, Note I, immediately preceding the quoted passage might also be of
    interest. In an earlier message I had casually compared the repeating circle
    with our averaging technique. This note reminds me that the two methods are
    different in one respect.
    In Note I, Mayer says that the final error of an observation is inverse
    proportional to the number of individual distances that have been accumulated
    into this observation. Therefore, if one assumes an instrument error of 2' to
    3', six observations are plenty sufficient to get the error below 30".
    In passing I remark that the goal for accuracy that Mayer sets himself is truly
    down to earth, much less ambitious than that of some of our list members! But
    my question is: Is his arithmetic right?
    It is right, if we assume that the observer is perfect and the only purpose of
    the averaging process is the elimination of instrument error and reading error
    (due to limited resolution of the division of the limb). This is what Mayer had
    in mind.
    When we average with a sextant, we are in a different situation. We can never
    get around the instrument error or the reading error with repeated readings.
    Our assumption is that the observer is not perfect and each observation is
    fraught with random error. This error is inverse proportional to the square
    root of the number of observations.  Given the above parameters, six
    observations would not be sufficient.
    If an imperfect observer producing random errors had a perfect sextant and a
    perfect repeating circle, the result of a repeated observation would be the
    same on both instruments (statistically). The error would obey the inverse
    square root law on both instruments. Mayer did not address this kind of error.
    He did not have the appropriate error theory. Might he have thought that he had
    divided random error by the number of observations, too? I don't know the
    Herbert Prinz

    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