Stephen,
ssystem.ini for 1P/Halley from MPC looks like this
Code:
[1phalley]
parent=Sun
orbit_Inclination=162.1905
coord_func=comet_orbit
orbit_Eccentricity=0.96715
orbit_ArgOfPericenter=112.293
absolute_magnitude=5.5
name=1P/Halley
orbit_Epoch=2455800.5
slope_parameter=3.2
lighting=false
tex_map=nomap.png
color=1.0, 1.0, 1.0
orbit_AscendingNode=59.3774
orbit_MeanMotion=0.0130342
orbit_MeanAnomaly=121.511
orbit_SemiMajorAxis=17.88185
albedo=0.04
radius=5
type=comet
This is taken from JPL/Horizons and
Andreas' parser (mine seems to be broken), and has more significant digits in the values. There have been no observations added to the data since 1994, so the numbers will not have changed in Stellarium's lifetime.
Code:
[1PHalley]
# Data taken from JPL/HORIZONS
# correct for the specified time frame:
# Start Time : A.D. 2011-Jul-11 00:00:00.0000 CT
# Stop Time : A.D. 2011-Jul-11 00:00:00.0000 CT
name = Comet 1P/Halley
parent = Sun
coord_func = comet_orbit
radius = 5.5
oblateness = 0.0
albedo = 1
lighting = true
halo = true
color = 1.0,1.0,1.0
tex_halo = star16x16.png
tex_map = nomap.png
orbit_Epoch = 2455753.500000000
orbit_TimeAtPericenter = 2446477.4971088152
orbit_PericenterDistance = 0.5884617797497997
orbit_Eccentricity = 0.9670918775720379
orbit_ArgOfPericenter = 112.2709434640211
orbit_AscendingNode = 59.35052908354584
orbit_Inclination = 162.1932522284531
# use M1 and k1 for the total magnitude of comets
# absolute_magnitude = M1 brightness when 1 AU from sun and 1 AU from earth
# slope_parameter = 0.4*k1 rate of brightening when approaching the sun
type = comet
absolute_magnitude = 5.5
slope_parameter = 3.2
Andrew