***** 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 following osculating orbital elements are consistent with orbit No.
37 for comet Giacobini-Zinner. Using these orbital elements and the export
version of the Astrometry Network's Two-Body Ephemeris Generation program,
users can generate their own ephemeris information. If care is taken to use
the set of orbital elements with the epoch of osculation closest to the
desired ephemeris dates, the Two-Body program can generate ephemeris
information that is equivalent to corresponding information in the perturbed
ephemeris (to approximately the one arc second level of accuracy). Each set
of orbital elements is in the same order as the elements listed above - the
only differences being that the epochs of osculation and dates of perihelion
passage time are given as Julian dates rather than calendar dates. The second
line of each element set contains the calendar date corresponding to the epoch
directly above it on the first line.
*** P/GIACOBINI-ZINNER TWO-BODY ELEMENTS ***
2445700.5 2446313.80826 1.0277733 0.7074560 172.50765 194.72648 31.88883
1984 JAN 1.0
2445760.5 2446313.78415 1.0278735 0.7074520 172.50306 194.72512 31.88666
1984 MAR 1.0
2445905.5 2446313.74234 1.0279973 0.7074700 172.49552 194.72187 31.88300
1984 JUL 24.0
2446010.5 2446313.72086 1.0280537 0.7074990 172.49097 194.71937 31.88110
1984 NOV 6.0
2446085.5 2446313.71462 1.0281091 0.7075130 172.48907 194.71629 31.87953
1985 JAN 20.0
2446135.5 2446313.71147 1.0281744 0.7075238 172.48668 194.71350 31.87852
1985 MAR 11.0
2446170.5 2446313.70885 1.0282203 0.7075369 172.48449 194.71158 31.87805
1985 APR 15.0
2446200.5 2446313.70682 1.0282472 0.7075499 172.48304 194.71017 31.87785
1985 MAY 15.0
2446225.5 2446313.70581 1.0282598 0.7075571 172.48261 194.70908 31.87782
1985 JUN 9.0
2446245.5 2446313.70540 1.0282658 0.7075591 172.48266 194.70825 31.87788
1985 JUN 29.0
2446260.5 2446313.70534 1.0282678 0.7075574 172.48291 194.70773 31.87798
1985 JUL 14.0
2446270.5 2446313.70541 1.0282682 0.7075542 172.48318 194.70744 31.87807
1985 JUL 24.0
2446280.5 2446313.70555 1.0282682 0.7075493 172.48348 194.70719 31.87817
1985 AUG 3.0
2446310.5 2446313.70601 1.0282677 0.7075240 172.48427 194.70676 31.87857
1985 SEP 2.0
2446345.5 2446313.70569 1.0282674 0.7074920 172.48399 194.70679 31.87883
1985 OCT 7.0
2446445.5 2446313.70702 1.0282850 0.7074944 172.48697 194.70542 31.87866
1986 JAN 15.0
2446515.5 2446313.71046 1.0283345 0.7075117 172.49304 194.70334 31.87887
1986 MAR 26.0
2446655.5 2446313.72280 1.0284169 0.7075378 172.50478 194.69813 31.88055
1986 AUG 13.0
2446755.5 2446313.73818 1.0285772 0.7075412 172.51722 194.69455 31.88229
1986 NOV 21.0
2446835.5 2446313.74355 1.0287378 0.7075237 172.52457 194.69371 31.88282
1987 FEB 9.0
Appendix
Observation Interpolation Program
The program OBSNTERP is an interactive, seven point Lagrange inter-
polation program that will return ephemeris data for periodic comet Giacobini-
Zinner over the interval January 5, 1984 through May 27, 1987. To run the
program, type OBSNTERP <carriage return> and respond to the prompts. The
executable requires a math co-processor. The Fortran source code is given in
the files labeled with the extension .FOR and the ephemeris data table for
comet Giacobini-Zinner is EPHEM.TAB. You can speed up the interpolation time
by shortening the data table to include only the interval that you require and
by requesting output for dates in chronological order. The information in the
data table was generated with IHW orbit number 37, which was based upon 1145
astrometric positions over the interval March 11, 1972 through March 31, 1987.
(Each line of the table is a fixed width of 110 characters plus <CR> <LF>.)
The definition of each output quantity is given below:
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