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: equinox
    From: Paul Hirose
    Date: 2004 Mar 21, 18:55 -0800

    Here's what I got from the JPL Horizons program. Note that 06:50:04 TT is about
    06:49:00 UTC. The USNO MICA program was pretty close to Horizons, about 2
    seconds of TT different.
    Ephemeris / MAIL_REQUEST Sun Mar 21 16:47:51 2004  Pasadena, USA / Horizons
    Target body name: Sun (10)                        {source: DE-0406LE-0406}
    Center body name: Earth (399)                     {source: DE-0406LE-0406}
    Center-site name: GEOCENTRIC
    Start time      : A.D. 2004-Mar-20 06:50:00.0000 TT
    Stop  time      : A.D. 2004-Mar-20 06:51:00.0000 TT
    Step-size       : 60 steps
    Center geodetic : 0.000000,     0.0000,     0.0000{E-lon(deg),Lat(deg),Alt(km)}
    Center cylindric: 0.000000,     0.0000,     0.0000{E-lon(deg),Dxy(km),Dz(km)}
    Center pole/equ : High-precision EOP model        {East-longitude +}
    Center radii    : 6378.1 x 6378.1 x 6356.8 km     {Equator, meridian, pole}
    Target pole/equ : IAU_SUN                         {East-longitude +}
    Target radii    : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole}
    Target primary  : Sun                             {source: DE-0406LE-0406}
    Interfering body: MOON (Req= 1737.400) km         {source: DE-0406LE-0406}
    Deflecting body : Sun, EARTH                      {source: DE-0406LE-0406}
    Deflecting GMs  : 1.3271E+11, 3.9860E+05 km^3/s^2
    Atmos refraction: NO (AIRLESS)
    RA format       : HMS
    Time format     : CAL
    Units conversion: 1 AU= 149597870.691 km, c= 299792.458 km/s, 1 day= 86400.0 s
    Table cut-offs 1: Elevation (-90.0deg=NO ),Airmass (>38.000=NO), Daylight (NO )
    Table cut-offs 2: Solar Elongation (  0.0,180.0=NO )
     Date__(TT)__HR:MN:SC.fff     R.A.__(airls-apparent)__DEC        CT-UT
     2004-Mar-20 06:50:00.000     00 00 00.0518 -00 00 00.065    64.185608
     2004-Mar-20 06:50:01.000     00 00 00.0544 -00 00 00.049    64.185608
     2004-Mar-20 06:50:02.000     00 00 00.0569 -00 00 00.032    64.185608
     2004-Mar-20 06:50:03.000     00 00 00.0594 -00 00 00.016    64.185608
     2004-Mar-20 06:50:04.000     00 00 00.0620 +00 00 00.001    64.185608
     2004-Mar-20 06:50:05.000     00 00 00.0645 +00 00 00.017    64.185608
     2004-Mar-20 06:50:06.000     00 00 00.0670 +00 00 00.034    64.185608
     2004-Mar-20 06:50:07.000     00 00 00.0696 +00 00 00.050    64.185608
    Column meaning:
      Terrestrial Dynamical Time, "TDT" or "TT", is used here. This uniform time
    scale is based on Atomic Time (TAI) and is extrapolated to pre-1955 dates.
    Any 'b' symbol in the 1st-column denotes a B.C. date. First-column blank (" ")
    denotes an A.D. date.  Calendar dates prior to 1582-Oct-15 are in the Julian
    calendar system.  Later calendar dates are in the Gregorian system.
      NOTE: "n.a." in output means quantity "not available" at the print-time.
     R.A._(airls-apparent)__DEC. =
       Airless apparent right ascension and declination of the target with respect
    to the Earth true-equator and meridian containing the Earth true equinox of
    date. Corrected for light-time, the gravitational deflection of light, stellar
    aberration, precession and nutation. Units: HMS (HH MM SS.ffff) and
    DMS (DD MM SS.fff)
     CT-UT =
       Difference between uniform Coordinate Time scale and Earth-rotation
    dependent Universal Time. Prior to 1962, the difference is with respect
    to UT1 (CT-UT1).  For 1962 and later, the delta is with respect to UTC
    (CT-UTC).  Values beyond the next July or January 1st may change if a
    leap-second is introduced. Units: SECONDS
    The Horizons home page is here:
    Horizons isn't friendly, at least not the email interface. I've learned to keep
    examples of successful command emails on file, so when I need to do something I
    have a starting point known to work. Today it took me multiple tries to figure
    out Horizons doesn't accept time step values in seconds. "Unknown units
    specification -- re-enter" isn't very helpful if the parameter with illegal
    units isn't stated.
    The system is fast, though. The table above is an excerpt from a 60-line table I
    requested from Horizons. Right after dispatching the command email I checked for
    a reply, and it was already waiting.
    On the other hand, it took more than a day to receive the "detailed example"
    mentioned at the bottom of the home page.
    By the way, I checked to see if lunarians could get precise separation angles
    between the Moon and other bodies via Horizons. No such luck. In fact, only
    solar system objects are available.

    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