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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Jack Aubrey's fixing of longitude
    From: Hewitt Schlereth
    Date: 2011 Jun 22, 09:44 -0400
    "Lunars can be ruled out as the necessary data was not available at the time."

    I dunno. Throughout the series there are quite a few mentions of Jack taking lunars.

    Hewitt

    On Wed, Jun 22, 2011 at 5:36 AM, Albert <alrodok@aol.com> wrote:

    Geoffrey

    In my oppinion, Patrick O'Brian's description is not just fiction. The situation on the island looks very real and reflects the considerable efforts made at the time to lay down far distant islands. Too bad that he does not say a word about the method…

    As with any other method to find the Greenwich time, Jack's procedure surely did not require the use of chronometers. Lunars can be ruled out as the necessary data was not available at the time. Regarding the lunar occultation, why should he rely on such a seldom event?

    I would like to slightly modify my first suggestion and offer two possible methods:

    a) By using a precision theodolite, he measured the azimut of the moon when her lower limb touched the horizon. Under certain circumstances, this value may differ as much as 0.2 minutes of arc for two observers 30 miles apart. And again "two seven four" would be the exact azimut.

    b) He measured the exact azimut of the moon and Venus just as they were vertically in line ("with Venus clear above her…). This value also differs for two observers.

    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?

    Get a NavList ID Code

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

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID 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