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
    or...
       
    Reply
    Re: Jack Aubrey's fixing of longitude
    From: Albert Rodok
    Date: 2011 Jun 24, 04:10 -0700

    Hi Frank,
    I enjoy very much this kind of brain storming. You guys are forcing me to put these old neurons of mine to work… Long time ago that I used to check our chronometers- just for the fun of it – by taking lunars. The very hard way – using trigonometric and logarithm tables – as neither a calculator nor lunar distance data were available on board.

    Regarding your remarks about using the azimuth: Yes, determining the precise moonset azimuth can be difficult, although it all depends on the atmospheric conditions. I have some times seen the moon going down clear, and in the tropics this is usually a fast event. As the azimuth is also sensitive to declination, the accuracy of the method depends on the actual "behavior" of the moon. Continuing with the brain storming: you could set the theodolite to a certain altitude (in order to avoid refraction problems), let's say 5°, and measure the azimuth when the moon reaches this altitude…

    As you see, I am trying to "rescue" the call "two seven four" for which the List has no explanation…

    At the moment I tend to another interpretation of this literary fantasy. As no lunar data for planets was available, I think that the occultation of Venus can also be ruled out, as an occultation (please correct me) is a special case of lunar (distance = 0). Nor was it a normal lunar, as the team was waiting for something to happen and a lunar can be taken any time.

    To sum up: they waited for the occultation of a star. And again, here comes the "azimuth man"…

    By measuring the exact azimuth you can reduce the local hour (angle), as now you have the precise declination and the local latitude. The Nautical Almanac gives you the Greenwich time for this event.

    You could of course use an artificial horizon and take a shoot of the moon, which however might become problematic if she is already very low (we never trusted altitudes of less than 15°).

    Albert

    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting 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