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Re: equinox
From: Paul Hirose
Date: 2004 Mar 21, 18:55 -0800
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: TIME 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: http://ssd.jpl.nasa.gov/horizons.html 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.