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JPLEPHREAD

JPLEPHREAD

Name


  JPLEPHREAD

Author


  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
  craigm@lheamail.gsfc.nasa.gov
  UPDATED VERSIONs can be found on my WEB PAGE:
      http://cow.physics.wisc.edu/~craigm/idl/idl.html

Purpose


  Open and read JPL DE200 or DE405 Ephemeride FITS File

Major Topics


  Planetary Orbits, Interpolation

Calling Sequence


  JPLEPHREAD, FILENAME, INFO, RAWDATA, JDLIMITS, STATUS=, ERRMSG=

Description



  JPLEPHREAD opens and reads the JPL DE200 or DE405 planetary
  ephemerides, as available in FITS format. The user must have the
  IDL Astronomy Library installed to use this routine.
  This routine is the initialization stage of a two-stage process to
  interpolate the JPL ephemeris. In this first stage, the file is
  opened, and the relevant portions of the table are read and stored
  into the two variables INFO and RAWDATA. In the second stage, the
  user actually interpolates the ephemeris for the desired bodies
  and to the desired ephemeris time using JPLEPHINTERP.
  Users must decide ahead of time the approximate dates of interest,
  and pass this range in the JDLIMITS parameter. Any date covered
  by the ephemeris is valid.
  JPLEPHREAD is able to read files of the following format:
    DE200 - Chebyshev - FITS format - Note 1
    DE405 - Chebyshev - FITS format - Note 1
    DE200 - Taylor - FITS format - Note 2
  Note 1 - Chebyshev formatted FITS files are available in the
            AXBARY package by Arnold Rots, found here:
              ftp://heasarc.gsfc.nasa.gov/xte/calib_data/clock/bary/
            or at the Markwardt FTP site:
              ftp://cow.physics.wisc.edu/pub/craigm/bary/
  Note 2 - Taylor-series based ephemerides have been available for
            years in the FTOOLS / LHEASOFT package produced by NASA's
            Goddard Space Flight Center. The original file is
            de200_new.fits, which covers the years 1959-2000,
            inclusive. A newer file is named
            de200_1950-2050_v2.fits, and covers the years 1959-2050.
            See Markwardt FTP site for these files.

Parameters



  FILENAME - name of ephemeris file (scalar string).
  INFO - upon completion, information about the ephemeris data is
          returned in this parameter in the form of a structure.
          Users must not modify INFO, although several fields are
          useful and may be accessed read-only:
              TSTART/TSTOP (start and stop time of data in Julian
                            days);
              C (speed of light in m/s);
              DENUM (development ephemeris number [200 or 405])
              AU (1 astronomical unit, in units of light-seconds)
  RAWDATA - upon completion, raw ephemeris data is returned in this
            parameter. Users are not meant to access this data
            directly, but rather to pass it to JPLEPHINTERP.
  JDLIMITS - a two-element vector (optional), describing the desired
              time range of interest. The vector should have the
              form [TSTART, TSTOP], where TSTART and TSTOP are the
              beginning and ending times of the range, expressed in
              Julian days.
              Default: entire table is read (note, this can be
              several megabytes)

Keyword Parameters



  STATUS - upon completion, a value of 1 indicates success, and 0
            indicates failure.
  ERRMSG - upon completion, an error message is returned in this
            keyword. If there were no errors, then the returned
            value is the empty string, ''.

Example



  Find position of earth at ephemeris time 2451544.5 JD. Units are
  in Astronomical Units.
  JPLEPHREAD, 'JPLEPH.405', pinfo, pdata, [2451544D, 2451545D]
  JPLEPHINTERP, pinfo, pdata, 2451544.5D, xearth, yearth, zearth, $
                /EARTH, posunits='AU'
   

References



  AXBARY, Arnold Rots.
      ftp://heasarc.gsfc.nasa.gov/xte/calib_data/clock/bary/
  HORIZONS, JPL Web-based ephermis calculator (Ephemeris DE406)
      http://ssd.jpl.nasa.gov/?horizons
 
  JPL Export Ephemeris FTP Site
      ftp://ssd.jpl.nasa.gov/pub/eph/planets/
      (ephemeris files are available here, however, they must be
      converted to FITS format using the "bin2eph" utility found in
      AXBARY)
  JPL Export Ephemeris CD-ROM - Ordering Information
      http://www.willbell.com/software/jpl.htm
  Standish, E.M. 1982, "Orientation of the JPL Ephemerides,
      DE200/LE200, to the Dynamical Equinox of J2000", Astronomy &
      Astrophysics, vol. 114, pp. 297-302.
  Standish, E.M.: 1990, "The Observational Basis for JPL's DE200,
      the planetary ephemeris of the Astronomical Almanac", Astronomy
      & Astrophysics, vol. 233, pp. 252-271.

See Also


  JPLEPHREAD, JPLEPHINTERP, JPLEPHTEST

Procedures Used


    FXBCLOSE, FXBOPEN, FXPAR(),
 

Modification History


  Written and Documented, CM, Jun 2001
  Use GETTOK() instead of STR_SEP() W. Landsman July 2002
  Add ephemeris file keywords to INFO, Jan 2002, CM
  Add fields to INFO to be consistent with JPLEPHMAKE, 04 Mar 2002, CM
  Correction of units for INFO.C (Thanks Mike Bernhardt), 2011-04-11, CM
  $Id: jplephread.pro,v 1.10 2011/06/27 18:44:44 cmarkwar Exp $



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