***** File EPHEM.TXT
EPHEMERIS
The geocentric ephemeris for 0h UT each day has been calculated by the
Astrometry Network from the following set of osculating orbital elements
(Astrometry Network orbit no. 37). The orbital solution was fit to 1145
astrometric observations over the interval from 1972 March 11 to 1987 March 31
with a rms residual = 1.1 arcsec. Full planetary and nongravitational
perturbations have been taken into account at each time step in the ephemeris
computations. The angular elements are referred to the ecliptic plane and the
equinox of 1950.
Epoch of Osculation 1985 Sept. 12.0 ET
Time of Perihelion Passage 1985 Sept. 5.20602 ET
Perihelion Distance 1.0282677 AU
Eccentricity 0.7075130
Argument of Perihelion 172.48430 deg.
Longitude of Ascending Node 194.70674 deg.
Inclination 31.87869 deg.
Nongravitational Parameters:
Radial component, A1 +3.166 E-09 AU/(day)**2
Transverse component, A2 -0.599 E-09 AU/(day)**2
The nongravitational acceleration model is outlined in the following
reference:
Marsden, B.G., Sekanina, Z., and Yeomans, D.K. Comets and
nongravitational forces. V. In Astronomical journal, v. 78, 1973,
p. 211 - 225.
The definition of each output quantity is given below:
(Each line of the table is a fixed width of 106 characters plus ❮CR❯ ❮LF❯.)
Date: Calendar date and Julian date (times in these ephemerides are
universal times).
RA, DEC: Geocentric right ascension and declination referred to the
mean equator and equinox of 1950.0 - light time corrections
have been applied.
DELTA: Geocentric distance of comet in AU.
DELDOT: Geocentric velocity of comet in km/sec.
R: Heliocentric distance of comet in AU.
RDOT: Heliocentric velocity of comet in km/sec.
THETA: Sun-Earth-Comet angle in degrees.
BETA: Sun-Comet-Earth angle in degrees.
MOON: Comet-Earth-Moon angle in degrees.
PSANG: Position angle of extended Sun-Comet vector.
PSAMV: Position angle of minus comet velocity vector.
(Position angles are measured east from north.)
Ravenel N. Wimberly
Astrometry Team Member
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
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