Spitzer heliocentric positions, velocities, and Julian dates We are currently planning to implement these calculations in the S16 software release of the Spitzer pipelines, which will go into operations early next year. Here is a sample snippet of the new information that will be added to the FITS headers of Spitzer image products: SPTZR_X = 6084048.364647 / Heliocentric J2000 x position (km) SPTZR_Y = -138993559.088106 / Heliocentric J2000 y position (km) SPTZR_Z = -62551818.282086 / Heliocentric J2000 z position (km) SPTZR_VX= 29.396946 / Heliocentric J2000 x velocity (km/s) SPTZR_VY= 0.639668 / Heliocentric J2000 y velocity (km/s) SPTZR_VZ= 0.729644 / Heliocentric J2000 z velocity (km/s) SPTZR_LT= 508.824176 / One-way light time to Sun's center (s) SCLK_OBS= 837186592.637 / SCLK (~sec. since 1/1/1980) at ramp start. ET_OBS = 205991150.144 / Ephemeris time (seconds past J2000 epoch) DATE_OBS= '2006-07-12T15:44:44.960' / UTC date & time at ramp start. MJD_OBS = 53928.6560759 / Mod. Julian Date (UTC) (days) at ramp start. HMJD_OBS= 53928.6558680 / Corresponding Heliocen. Mod. Julian Date UTCS_OBS= 205991084.960 / UTC seconds past year 2000 at ramp start. The inertial reference frame for the calculations is ICRF, with its origin at the Sun's center. The target used for computing helocentric Julian data is specified by RA_RQST and DEC_RQST in the FITS header. Note that since the range of the target is unavailable, it is impossible to include a correction for the target's Spitzer/Sun parallax. In the meantime, if you urgently require this information for a given target and specific Spitzer SCLK values, you are welcome to submit a Spitzer Helpdesk question and we will do our best to accommodate your request in a timely manner. An old (but still working way) to get heliocentric states of Spitzer with respect to the Sun-center. Either: 1) Mail the file at the very end of this file as a plain-text message to "horizons@ssd.jpl.nasa.gov" ... with subject "JOB". It will return heliocentric states of Spitzer with respect to Sun-center. Edit the file to change times, output steps, aberration corrections, etc. Or: 2) To do this interactively, to understand what is going on: telnet ssd.jpl.nasa.gov 6775 (command line) telnet://ssd.jpl.nasa.gov:6775 (browser window URL) type (in response to prompts): -79 e v @10 f 2005-jan-4 2005-jan-14 1d The results will be computed and displayed. They can be e-mailed or FTP'ed by the user as preferred. Type ? or ?! at any prompt for an explanation of the prompt, if they wish to vary from the example above. OUTPUT WILL LOOK LIKE THIS ******************************************************************************* Ephemeris / PORT_LOGIN Fri Dec 3 12:10:56 2004 Pasadena, USA / Horizons ******************************************************************************* Target body name: Spitzer Space Telescope (-79) {source: pfile.nio} Center body name: Sun (10) {source: DE-0406LE-0406} Center-site name: BODYCENTRIC ******************************************************************************* Start time : A.D. 2005-Jan-04 00:00:00.0000 CT Stop time : A.D. 2005-Jan-14 00:00:00.0000 CT Step-size : 1440 minutes ******************************************************************************* Center geodetic : 0.000000, 0.000000, 0.00000 {E-lon(deg),Lat(deg),Alt(km)} Center cylindric: 0.00000, 0.000, 0.000 {E-lon(deg),Dxy(km),Dz(km)} Center radii : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole} Output units : AU-D Output format : 03 Reference frame : ICRF/J2000.0 Output type : GEOMETRIC cartesian states Coordinate systm: Earth Mean Equator and Equinox of Reference Epoch ******************************************************************************* JDCT X Y Z VX VY VZ LT RG RR ******************************************************************************* $$SOE 2453374.500000000 = A.D. 2005-Jan-04 00:00:00.0000 (CT) -7.609682013429106E-02 9.154791873490874E-01 4.114832195678167E-01 -1.713478357059860E-02 -1.234555880333105E-03 -8.133909810289680E-04 5.813544227402228E-03 1.006583979849566E+00 -1.599512941958680E-04 2453375.500000000 = A.D. 2005-Jan-05 00:00:00.0000 (CT) -9.321974899059239E-02 9.141118598628044E-01 4.106101623850374E-01 -1.711024393478818E-02 -1.500054002281918E-03 -9.326905952650625E-04 5.812625573753074E-03 1.006424919900919E+00 -1.581605768905870E-04 2453376.500000000 = A.D. 2005-Jan-06 00:00:00.0000 (CT) -1.103156480885221E-01 9.124791826559124E-01 4.096179098668365E-01 -1.708072460417264E-02 -1.765242188304123E-03 -1.051775740826879E-03 5.811717401015029E-03 1.006267674665776E+00 -1.563219501222729E-04 2453377.500000000 = A.D. 2005-Jan-07 00:00:00.0000 (CT) -1.273795396405996E-01 9.105815050715770E-01 4.085066942145562E-01 -1.704622964991585E-02 -2.030041617293819E-03 -1.170610953240682E-03 5.810819984438392E-03 1.006112291802249E+00 -1.544359191363143E-04 2453378.500000000 = A.D. 2005-Jan-08 00:00:00.0000 (CT) -1.444064507007346E-01 9.084192552895924E-01 4.072767830894525E-01 -1.700676468429686E-02 -2.294373441466383E-03 -1.289160779128745E-03 5.809933596311451E-03 1.005958818455594E+00 -1.525030043828000E-04 2453379.500000000 = A.D. 2005-Jan-09 00:00:00.0000 (CT) -1.613914147072323E-01 9.059929403399337E-01 4.059284795956564E-01 -1.696233686439338E-02 -2.558158812638683E-03 -1.407389788108522E-03 5.809058505872969E-03 1.005807301243057E+00 -1.505237414087019E-04 2453380.500000000 = A.D. 2005-Jan-10 00:00:00.0000 (CT) -1.783294730291898E-01 9.033031460899434E-01 4.044621222512004E-01 -1.691295489517730E-02 -2.821318908680434E-03 -1.525262584759726E-03 5.808194979225336E-03 1.005657786238839E+00 -1.484986807405493E-04 2453381.500000000 = A.D. 2005-Jan-11 00:00:00.0000 (CT) -1.952156765157134E-01 9.003505372050140E-01 4.028780849470683E-01 -1.685862903201086E-02 -3.083774960130354E-03 -1.642743820657463E-03 5.807343279248631E-03 1.005510318959215E+00 -1.464283877651264E-04 2453382.500000000 = A.D. 2005-Jan-12 00:00:00.0000 (CT) -2.120450870472106E-01 8.971358570824424E-01 4.011767768940716E-01 -1.679937108255240E-02 -3.345448276935179E-03 -1.759798206445529E-03 5.806503665514289E-03 1.005364944347585E+00 -1.443134425727788E-04 2453383.500000000 = A.D. 2005-Jan-13 00:00:00.0000 (CT) -2.288127790885268E-01 8.936599277587458E-01 3.993586425578484E-01 -1.673519440803050E-02 -3.606260275377800E-03 -1.876390524000370E-03 5.805676394201896E-03 1.005221706760070E+00 -1.421544398587410E-04 2453384.500000000 = A.D. 2005-Jan-14 00:00:00.0000 (CT) -2.455138412428061E-01 8.899236497897173E-01 3.974241615814506E-01 -1.666611392392464E-02 -3.866132505078226E-03 -1.992485638604044E-03 5.804861718014359E-03 1.005080649950823E+00 -1.399519887574192E-04 $$EOE ******************************************************************************* Coordinate system description: Earth Mean Equator and Equinox of Reference Epoch Reference epoch: J2000.0 xy-plane: plane of the Earth's mean equator at the reference epoch x-axis : out along ascending node of instantaneous plane of the Earth's orbit and the Earth's mean equator at the reference epoch z-axis : along the Earth mean north pole at the reference epoch Symbol meaning [1 AU=149597870.691 km, 1 day=86400.0 s]: JDCT Epoch Julian Date, Coordinate Time X x-component of position vector (AU) Y y-component of position vector (AU) Z z-component of position vector (AU) VX x-component of velocity vector (AU/day) VY y-component of velocity vector (AU/day) VZ z-component of velocity vector (AU/day) LT One-way down-leg Newtonian light-time (day) RG Range; distance from coordinate center (AU) RR Range-rate; radial velocity wrt coord. center (AU/day) Geometric states/elements have no aberration corrections applied. Computations by ... Solar System Dynamics Group, Horizons On-Line Ephemeris System 4800 Oak Grove Drive, Jet Propulsion Laboratory Pasadena, CA 91109 USA Information: http://ssd.jpl.nasa.gov/ Connect : telnet://ssd.jpl.nasa.gov:6775 (via browser) telnet ssd.jpl.nasa.gov 6775 (via command-line) Author : Jon.Giorgini@jpl.nasa.gov ******************************************************************************* >>> Select... [A]gain, [N]ew-case, [F]tp, [K]ermit, [M]ail, [R]edisplay, ? : E-MAIL BATCH REQUEST TO SEND TO HORIZONS !$$SOF ! ! Example e-mail command file. If mailed to "horizons@ssd.jpl.nasa.gov" ! with subject "JOB", results will be mailed back. ! ! This example demonstrates a subset of functions. See main doc for ! full explanation. Send blank e-mail with subject "BATCH-LONG" to ! horizons@ssd.jpl.nasa.gov for complete example. ! EMAIL_ADDR = ' ' ! Send output to this address ! (can be blank for auto-reply) COMMAND = '-79' ! Target body, closest apparition OBJ_DATA = 'YES' ! No summary of target body data MAKE_EPHEM = 'YES' ! Make an ephemeris START_TIME = '2005-Jan-04 00:00' ! Start of table (UTC default) STOP_TIME = '2005-Jan-21 00:00' ! End of table STEP_SIZE = '1 day' ! Table step-size TABLE_TYPE = 'VECTOR' ! Specify VECTOR ephemeris table type CENTER = '@10' ! Set observer (coordinate center) REF_PLANE = 'FRAME' ! J2000 equatorial plane VECT_TABLE = '3' ! Selects output type (3=all). OUT_UNITS = 'KM-S' ! Vector units; KM-S, AU-D, KM-D CSV_FORMAT = 'NO' ! Comma-separated output (YES/NO) VEC_LABELS = 'YES' ! Label vectors in output (YES/NO) VECT_CORR = 'NONE' ! Correct for light-time (LT), ! or lt + stellar aberration (LT+S), ! or (NONE) return geometric ! vectors only. !$$EOF