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: Back In Hobby: Some Questions, Please
    From: Alexandre Eremenko
    Date: 2007 Apr 30, 11:54 -0400

    > You wrote:
    > Were these altitudes taken at
    > night using a sea horizon? (...one last hope
    > for a sensible explanation).
    No, they were taken in conjunction with Sun-Lunar
    distances. Thus Sun was shining.
    On May 1774 (my first two postings under Point Venus)
    they were taken with ordinary sextant/quadrant,
    against a sea horizon, but the height of the observer
    over the horizon was not recorded.
    On August 27 1773 (my last posting on Point Venus)
    they were taken with astronomical quadrant using
    a plumb line instead of the horizon.
    I have the following possible explanation.
    The timing of these altitudes was not done carefully.
    Presumably they used one clock with which three
    simultaneous observations were timed
    (Sun alt, Moon alt and the Lunar).
    Of course they took most care to time the Lunar.
    So perhaps when the guy taking the lunar said "Now!"
    the person in charge of the clock recorded the time.
    The two other guys taking altitudes did not give
    separate commands to record the time, and tried to
    record their altitudes approximately at the time
    when they heard this "Now" signal.
    This could easily lead to several seconds or more mismatch
    in the timing of altitudes. And the altitudes change
    This is my conjecture.
    In any case it seems clear that they did not really care
    much about accuracy of these altitudes.
    Perhaps they dod not inspect the verniers with magnifying glass
    being afraid to miss the next "Now" from the Lunar guy.
    But I even don't know whether their
    sextants/quadrants were equipped
    with any magnifying glasses. Probably not, as they had
    large radii.
    There can be other explanations as well: the corral reef/waves
    obscuring the horizon under Moon... etc.
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com

    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