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: Lunar altitudes
    From: Jan Kalivoda
    Date: 2003 Apr 14, 20:34 +0200

    The end form of the error equation for the method of finding GMT by lunar altitudes is:
    dRA of Moon = sec l (cosec az dalt - cosec AZ dALT)
    d - error of a value
    RA - Right Ascension (its error creates error of the GMT found through 
    interpolation for GMT according to RA of the Moon)
    l - latitude of the observer
    AZ, az - azimuths of the Moon and of the star in the time of observation
    ALT, alt - altitudes of ..... (dtto)
    This equation affirms all details said about errors of the method in this thread during the last days.
    Therefore, if George pledges regularity of refraction above 10 degrees, this 
    method should be very accurate above the artificial horizon :)
    Jan Kalivoda
    ----- Original Message -----
    From: "George Huxtable" 
    Sent: Monday, April 14, 2003 7:23 PM
    Subject: Re: Lunar altitudes
    > Jan Kalivoda said-
    > >George is fully right in my opinion. For neutralizing the errors in both
    > >altitudes owing to irregular dip, only their azimuths matter and the
    > >nearer they are, the better.
    > >
    > >But for neutralizing the effects of irregular refraction on both
    > >altitudes, the altitudes are more important, although the azimuths can be
    > >relevant as well.
    > >
    > >And of course, the time of both observations should be the same, otherwise
    > >a change of atmospheric conditions can wreck the result completely.
    > >
    > >Therefore the advice of old authors seems logical - the same time,
    > >neighbouring azimuths, neighbouring altitudes of both bodies; and both
    > >should stay near the prime vertical, so that both LHA's obtained might be
    > >as reliable as possible. These are the cases 1) and 2) in George's reply.
    > =================
    > I'm going to quibble a bit further here.
    > It can only be when the azimuth difference between the two bodies is small,
    > that there's any advantage at all to be gained in arranging the two
    > altitudes to be similar.
    > And unlike the refraction-component of dip, refraction at higher altitudes
    > (above 10 deg, say) is well understood and well predicted, shows little
    > variation with local atmospheric conditions (and those variations are
    > readily calculated). Therefore, I think that the "advice of old authors"
    > (to arrange that the altitudes of the two bodies should be similar) is
    > without any firm foundation. At such altitudes, I doubt that "irregular
    > refraction" is of any importance: but I am ready to be convinced otherwise.
    > George Huxtable
    > ================================================================
    > contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > ================================================================

    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