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: September Equinox computation
    From: Jay Borseth
    Date: 2002 Sep 24, 13:09 -0700

    There is a C version of Novas which can use the DE200 ephemeris
    available at http://aa.usno.navy.mil/AA.  Pocket Stars
    (www.nomadelectronics.com) uses the C version of Novas and DE405.  You
    can look on the bibliography section on the download page for more info
    on merging JPL and Novas.
    
    The results I'm getting put the equinox at:
    
       4:51:54 AM GMT on 23 Sep 2002, crossing at E 105 degrees 9' 56".
    
    - Jay
    
    -----Original Message-----
    From: Navigation Mailing List
    [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] On Behalf Of Dan Allen
    Sent: Tuesday, September 24, 2002 9:29 AM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Re: September Equinox computation
    
    
    On Tuesday, September 24, 2002, at 04:43 AM, Pierre Boucher wrote:
    
    > Which method would you use to PRECISELY compute (hh-mm-ss) the
    > September equinox?
    
    This is actually a fairly hard problem.  We usually know that the
    equinox has a declination of zero and a right ascension of 12:00:00
    hours in September.
    
    My computation calculates the position of the sun using the Meeus
    formulas and iterates with a secant root finder to find when the
    declination is zero, or when the right ascension is 12:00:00.  The hard
    part is that our mathematical models do not always have a time when
    these two quantities have these two desired values.
    
    I always seem to be a few minutes off of what the Naval Observatory says
    is the beginning of Fall and I have discussed this with a friend at the
    Jet Propulsion Laboratories (JPL) and he says that what I need to get
    the "right" answer is the full DE200 emphemeris package, which is huge
    and largely in Fortran. Alas, I am a C programmer.
    
    Dan Allen
    
    PS - My computations for this year put the equinox at 4:52:04 AM GMT on
    23 Sep 2002.
    
    
    

       
    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