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
    Azimuth / elevation from sextant observations
    From: Paul Hirose
    Date: 2019 Jul 30, 14:26 -0700

    On 2019-07-30 8:16, Peter Monta wrote:
     > If you're observing from a fixed spot, and you know the
     > direction to a distant landmark, then that's just as good as a sea
    horizon
     > (in fact better, since the landmark is likely to be at least a few
    degrees
     > above the true horizon and thus in a better atmospheric path).  The
     > direction (i.e. topocentric azimuth and elevation) can be found with
    (what
     > else?) celestial, using either a sextant or a theodolite.
    
    Several years ago I had a dream in which I was observing sextant angles
    between a distant mountain peak and the Sun. Upon waking I remembered
    the dream with unusual clarity, and on further reflection I realized it
    was possible to measure azimuths and elevations of landmarks that way.
    
    Any sight reduction method can be used. With traditional paper and
    pencil techniques, begin with a plotting sheet. True north takes the
    place of the prime meridian. The estimated elevation and azimuth of the
    landmark are the dead reckoning latitude and longitude.
    
    In this application, time and position are known, so the celestial
    body's azimuth and refracted altitude are also known. In the sight
    reduction these become "GHA" and "declination".
    
    For observed altitude, use 90 minus the sextant angle.
    
    The sight reduction will yield azimuth and intercept. "Azimuth" is
    actually the position angle (in a horizontal coordinate system) of the
    body with respect to the landmark. But on the plotting sheet it's
    equivalent to computed azimuth.
    
    Elevation angles determined by this method are affected by terrestrial
    refraction. That's not necessarily a bad thing. It might be interesting
    to analyze the variability of terrestrial refraction. If the landmark is
    a distant isolated light you can observe all night with a wide choice of
    stars.
    

       
    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