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 km/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.200', 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.html
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