Thanks Andrew and Barry.
I entered the data from Ians page
http://astroblogger.blogspot.com/201...tellarium.html
[Encke]
name = 2P/Encke
parent = Sun
radius = 24
oblateness = 0.0
halo = true
color = 1.0,1.0,1.0
tex_halo = star16x16.png
tex_map = nomap.png
coord_func = comet_orbit
orbit_TimeAtPericenter = 2455415.077574995
orbit_PericenterDistance = 0.3369758246572427
orbit_Eccentricity = 0.8479456370992317
orbit_ArgOfPericenter = 186.4988142344296
orbit_AscendingNode = 334.5696032945518
orbit_Inclination = 11.78284902989807
lighting = false
albedo = 1
sidereal_period = 365.25
Is not working ... is there anything else I should be doing?