Help for EPHEMERIS

PURPOSE:
To compute information about the way one planet looks when viewed from another.
Computed quantities are:
Object range in km.
Object planetocentric west longitude in degrees.
Object planetocentric latitude in degrees.

EXECUTION:
Example:
To see the orientation of jupiter as viewed from the earth on February 21 1996
at 12 hours 23 minutes 14.6 seconds GMT.

ephemeris viewer=earth object=jupiter epoch="21 Feb 1996 12 23 14.6"


METHOD:
Spice file de403s.bsp is consulted for the ephemeris information. 
A light time correction is included.

The approximate time coverage for the bodies listed is:
 
   From: December 1, 1979
   To  : January  7, 2011

   As of November 13, 1995 this is the official ephemeris planned
   for use by the flight projects: Cassini, Mars Pathfinder, Mars
   Global Surveyor, Near Earth Asteroid Rendezvous.

Accuracy
 
   The JPL "DE" series of planetary ephemerides have been widely used
   throughout the astronomical community for over 20 years.  They have
   been put to many different uses.  A short list of the applications
   of these ephemerides includes:  the construction of the tables in
   the "Astronomical Almanac" (for that matter all almanac producers
   world wide), planning of solar system observations with the Hubble
   Space Telescope, navigation of interplanetary missions, lunar laser
   ranging, solar system radar ranging, and solar system observations
   via VLBI.
 
   This latest ephemeris, DE403, represents state-of-the-art planetary
   and lunar positions.
 
   One method of describing the accuracy of the positions provided in
   DE403 is to consider the angles between various ephemeris objects
   as viewed from Earth.
 
   If the two objects observed are taken from the list (Sun, Mercury,
   Venus, Mars, Moon) the angles computed from the ephemeris positions
   are accurate to one or two milli-arcsecond.(This assumes all
   appropriate corrections are applied for light time, stellar
   aberration, and relativistic effects to the ephemeris derived
   positions.)  If you add the barycenter of Jupiter to this list,
   uncertainty in ephemeris derived angles may grow to a few hundredths
   of an arcsecond.  Adding Saturn, Uranus and Neptune will raise the
   uncertainty level to approximately 0.1 arcseconds.  Finally, adding
   Pluto to the list raises the observable errors to 0.3 arcseconds
   for the present and increasing into the future.
 
   Radial distances to the centers of objects follow a similar trend.
   The radial distances between the inner objects of the solar system
   as computed via the ephemeris are accurate to 1 to 2 km.  The
   distance between the Earth and the Jupiter Barycenter is accurate
   to better than 10 km.
 
   The uncertainty in the distances to Saturn, Uranus and Neptune are
   approximately 1000, 2000 and 4000 km respectively.  For Pluto, the
   radial distance from earth may be in error up to 10000 km for the
   present and growing into the future.
 
   The above statements refer to the internal consistency of the
   ephemeris.  These statements of accuracy also hold when comparing
   positions with the J2000 radio source reference frame adopted by
   the IAU and IERS.
   When comparing the position a planet (other than Pluto) as seen
   from earth  with  catalogue positions of stars,  the DE403 positions
   of the planets are very likely to be more accurate than knowledge
   of the positions of the stars in the catalog (with the possible
   exception of the Hipparchos catalog). In the case of Pluto, the
   error in the DE403 position of Pluto is likely to be close to the
   error in the catalogue positions of stars.
 
References
 
   Jet Propulsion Laboratory Interoffice Memorandum IOM 314.10-127
   by E.M. Standish, X.X. Newhall, J.G. Williams and W.M. Folkner
   "JPL Planetary and Lunar Ephemerides, DE403/LE403"
 
Inquiries
 
   If you have any questions regarding this ephemeris contact
   NAIF team member
 
   Bill Taber
   (818) 354-4279
   btaber@spice.jpl.nasa.gov
 
   or NAIF group head
 
   Chuck Acton
   (818) 354-3869
   cacton@spice.jpl.nasa.gov
 
HISTORY:
3-1-97  J Lorre. 
COGNIZANT PROGRAMMER:  Jean Lorre
REVISIONS:
  10 SEP 98  GMY  Allow for input of planet or barycenter SPK data.
  21 JUL 1998 TIH Replace xgetenv_vic, clpool and ldpool with init_spice
                  which uses new spice subroutines (AR-100456)
  20 MAR 98  GMY  Fix parsing of epoch (AR 9682)

PARAMETERS: