in search of moons

Last night we tried to see Oberon and Titania around Uranus. I think I saw Oberon below the planet (in the C14). Isaac was certain he was seeing Titania above.

We then thought it would be good to try Triton orbiting Neptune. Ed T, after some research, suggested it should be quite possible, at a magnitude of 13.something. He reminded us that it is one of the larger moons in the solar system (it's 7th).

Last night we found neither TheSky6 nor Stellarium showed the Neptunian moons.

I decided to add the missing solar system data into Stellarium. I first looked in the JPL SSD site but it seems the small body browser is not for moons. I was referred to the HORIZONS site but it looked like it was only going to give ephemerides. Still, I initiated a search for Oberon, just to see if Stellarium data agreed with the current figures.

Well, it did offer up some handy data for Oberon (704): semi-major axis (km): 582.6 (10^3); orbital period: 13.463 d; eccentricity: 0.0008; rotational period: synchronous; inclination (deg): 0.10. I pulled the ssystem.ini for Stellarium. Huh. It's format is very different than what I've seen for asteroids and comets... To the point that I could not tell if Stellarium was right or not. So much for that.

All of this jostled a memory of enquiries to the Stellarium team about plotting Neptune's moons. I had a vague recollection that it required the use of a subversion. I wondered if I'd need to download it... After some frustrating but brief searching of the SourceForge forum, I found a dump of content needed for Triton and Nereid.

[triton]
name = Triton
parent = Neptune
radius = 1353.4
oblateness = 0.0
albedo = 0.76
lighting = true
halo = false
color = 1.0,1.0,1.0
tex_halo = NULL ;star16x16.png
tex_map = asteroid.png
rot_periode = 16.11
rot_rotation_offset = 71.5
rot_obliquity = 156.8
coord_func = ell_orbit
orbit_Epoch = 2447763.5
orbit_Period = 5.8768541
orbit_SemiMajorAxis = 354765.286
orbit_Eccentricity = 0.00002285
orbit_Inclination = 156.826240
orbit_AscendingNode = 147.899288
orbit_LongOfPericenter = 293.092400
orbit_MeanLongitude = 315.726316

[nereid]
name = Nereid
parent = Neptune
radius = 170
halo = false
color = 1.,0.9,0.75
tex_map = asteroid.png
tex_halo = NULL ;star16x16.png
lighting = true
albedo = 0.16
rot_periode = 11.52
rot_rotation_offset = 0.0
rot_obliquity = 0.0
coord_func = ell_orbit
orbit_Epoch = 2447763.5
orbit_Period = 360.13619
orbit_SemiMajorAxis = 5513400.
orbit_Eccentricity = 0.7512
orbit_Inclination = 6.68
orbit_AscendingNode = 190.678
orbit_LongOfPericenter = 17.690
orbit_MeanLongitude = 36.056

I decided to conduct an experiment. What's the worst that could happen? I copied the code (dated 1 Jul 2009). Saved the ssystem.ini file. Restarted Stellarium. Located Neptune. Zoomed it. Hey! There it was: Triton! OK!

We'll have to look for Neptune's biggest moon later tonight...