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: Any "on line" Star Position Computation available ?
    From: Andrés Ruiz
    Date: 2011 Jun 21, 08:17 +0200
    Trying to do some tests, I have upgrade my soft to the last NOVAS version 3.1 and find discrepancies in the results.
    Here is the kindly answer of USNO.

    ---------- Forwarded message ----------
    From: AA Help <help{at}aa.usno.navy.mil>
    Date: 2011/6/20
    Subject: RE: GHA of Aries using NOVAS 3.1
    To: Andres Ruiz <navigationalalgorithms---.com>
    Cc: AA Help <help{at}aa.usno.navy.mil>


    Without delving too deeply into your NOVAS code, the software that generates our celestial navigation table (http://aa.usno.navy.mil/cgi-bin/aa_flamenav.pl) has been neglected. It is stiill based on NOVAS F2.0, which does not include the most recent models for nutation and precession. The file of Delta-T values is uses for computations does not appear to have been updated since 2000. We discovered these shortcomings recently when the software had to be recompiled to accomodate a server upgrade. We will be updating that service shortly.

    You did not mention which NOVAS C3.1 version of solarsystem you are using; the software that generates the celestial navigation table uses SOLSYS version 2 (the Fortran equilivant of solarsystem version 2) with JPL ephemeris DE200. Most of our other services that use an external ephemeris now use JPL ephemeris DE405.



    Respectfully,



    Astronomical Applications Dept.

    U.S. Naval Observatory

    Washington, DC

    ________________________________
    From: Andres Ruiz [navigationalalgorithms---.com]
    Sent: Monday, June 20, 2011 8:25 AM
    To: AA Help
    Subject: GHA of Aries using NOVAS 3.1

    Dear NOVAS support,

    I have some difficulties calculating GHA of Aries with NOVAS 3.1
    The C code is this:

    short int NauticalAlmanac( BodyNovas celestialBody, char *starName,
    short int year, short int month, short int day, double h, double m, double s,
    double leap_secs, double ut1_utc,
    double *ra, double *dec, double *gha,
    double *sd, double *hp,
    double *eot,
    double *illumination, char *fase )
    {
    double gast, last, theta;
    const short int accuracy = 0; // full accuracy

    ////
    ///
    // Aries
    double utc     = (double)h+(double)m/60.0+(double)s/3600.0;
    double ut1     = utc + ut1_utc/3600.0; // h
    double delta_t = 32.184 + leap_secs - ut1_utc; // s

    double jd_utc = julian_date( year, month, day, utc );
    double jd_ut1 = jd_utc + ut1_utc / 86400.0;  // UT1 Julian Dates

    // Greenwich apparent sidereal time
    if( (error = sidereal_time( jd_ut1, 0.0, delta_t, 1, 1, accuracy, &gast )) != 0 ) {
    fprintf( logF, "Error %d from sidereal_time.", error);
    return (error);
    }

    *gha = ang_0_360( 15.0*(gast) );  // 0º <= gha < 360º

    ////
    ///
    }



    With this program based in NOVAS 3.1 I have obtained : GHA_ARIES = 211º 40.8'
    date UTC UT1 TT UTCjd TTjd UT1jd dT objt GHA
    24/04/2011 0:00:00 _00:00:0.23339 _00:01:6.18400 2455675.5 2455675.501 2455675.5 66.41739 Aries 211º 40.8'
    With http://aa.usno.navy.mil/cgi-bin/aa_flamenav.pl and with my own calculations based in Meeus´s "Astronomical algorithms" GHA_ARIES = 211º 40.9'
    GAST = 14:06:43.49917

    Why this 0.1' error?

    Could You help me? What I am doing wrong?
    Best regards

    --
    Andrés Ruiz
    Navigational Algorithms
    http://sites.google.com/site/navigationalalgorithms/

       
    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