Newbie: Voyager 2-Triton encounter?

[granthutchison]

Thanks, Selden. The other obvious problems are the V1 and V2 flybys of Jupiter; in both cases the moons are not in their correct positions, but the planet itself looks fine. I wonder whether anyone else has encountered this and tried to put together some samples for those events as well.

Two difficulties there - one is that the current CustomOrbits for the Galileans are rotated by ~20 degrees, again because of a conversion problem in the ascending node position. Beyond that, there are minor errors in the CustomOrbit positions of the Galileans (and Jupiter), sufficient to distort close encounters and mutual eclipses.
Chris should certainly have the big error fixed in the next edition of Celestia, but the smaller positional errors might take a bit more ironing out, and perhaps a trade-off between speed and accuracy.

Grant

[fisher]

Grant, how do I fix the 20-degree error in the ascending nodes, then? I'm not sure whether my orbital data for the Galileans is up to date or not. For example, here is what I have for Io; should my AscendingNode be 292.981 or 332.981? Or is there an entirely different value I can edit?

"Io" "Sol/Jupiter"
{
Texture "io180.jpg" #revised texture map with central prime meridian
# Texture "io2k.dds"
Radius 1821
CustomOrbit "io"
EllipticalOrbit
{
Epoch 2443000.00038375
Period 1.769138
SemiMajorAxis 421600
Eccentricity 0.0041
Inclination 0.040
AscendingNode 312.981
LongOfPericenter 97.735
MeanLongitude 106.724
}
RotationOffset 198 #correct orientation for map with central prime meridian
Albedo 0.61
}

P.S.: I've been trying to match Celestia to the predicted transit/shadow/etc. events for the Galilean moons as given by S&T (in turn based on the Bureau des Longitudes) but it's not even close, even accounting for the light-time difference. Do I have some bad numbers here?

Thanks,
Alex

[granthutchison]

Alex:

Grant, how do I fix the 20-degree error in the ascending nodes, then?

You can't, because Celestia is using a CustomOrbit for the Galileans (computed by a routine within the program itself) - the elliptical elements are shown merely for reference. It's the CustomOrbit in the current version of Celestia which contains the errors, and you can't modify that through solarsys.ssc. No choice but to wait for Chris to make the changes and release a new version.
I can reproduce individual events by defining appropriate elliptical elements and "commenting out" the call to CustomOrbit, but the Galileans have sufficiently variable orbits that any single elliptical definition very rapidly diverges from real events - I can, for instance, produce four or five days' worth of good eclipses and occultations, but then I start to lose alignment.

Grant

[fisher]

OK - nothing to do then but sit tight and wait. Thanks for the help!

Alex

[chris]

Alex:

Grant, how do I fix the 20-degree error in the ascending nodes, then?

You can't, because Celestia is using a CustomOrbit for the Galileans (computed by a routine within the program itself) - the elliptical elements are shown merely for reference. It's the CustomOrbit in the current version of Celestia which contains the errors, and you can't modify that through solarsys.ssc. No choice but to wait for Chris to make the changes and release a new version.
I can reproduce individual events by defining appropriate elliptical elements and "commenting out" the call to CustomOrbit, but the Galileans have sufficiently variable orbits that any single elliptical definition very rapidly diverges from real events - I can, for instance, produce four or five days' worth of good eclipses and occultations, but then I start to lose alignment.

I do have the Galilean moons mostly fixed now; longitude (wrt to Jupiter's equatorial plane) seems to agree completely with Horizons data, but the latitude is still a slight bit off.

The accuracy of the positions of Jupiter and other major planets is quite good (less than an arc second error if you're observing from Earth), but it's not good enough for close flybys of small satellites. The two choices are: use more VSOP87 terms for computing the orbits (which slows Celestia down), or use the JPL DE405 ephemeris files (which is faster and more accurate, but consumes a lot of memory for long time spans.)

--Chris

[Guest]

Chris, where can I get the most up-to-date orbital data for the Galilean moons, then (or is it not ready yet)? Thanks!

Alex

[HankR]

It seems reasonable to expect that certain events (such as close spacecraft flybys, satellite mutual eclipses, etc. ) will require very precise positional data which is not needed most of the time. Perhaps it would be possible to support user-supplied hi-resolution positional data for specific time intervals as a supplement to lower-resolution positional data that would be used by default the rest of the time.

- Hank

[selden]

Hank,

I agree with you, but I'd like to spell out the details.

The Beginning and Ending directives already let you do this to a certain extent.

The best calculations of planetary and satellite positions require as many as a thousand terms in their orbital formulae. If Celestia does them, these calculations have to be performed in realtime between one screen update and the next for every object in the field of view. If you use heliocentric xyz trajectories, then the calculations don't have to be done in realtime -- Horizons does it for you and it can take as long as it needs to.

However, for the positions to be as accurate as we'd like, the xyz coordinates will have to use double precision values for locations around the outer planets. Right now Celestia only stores xyz trajectories in single precision. To minimize the storage space needed, Celesita also will have to be modified to use something better than the linear interpolation that it currently does between adjacent xyz position samples. That'd reduce the number of points that need to be stored back doen to a managable level.

[ou8poop2]

umm,...
Grant, maybe you could post your scc info for neptune as well. mine seems a bit skewed, because when i add your triton info in, im still 207,000 km from it at Voyager's closest approach. I probably either have old data, or screwed it up along the way somehow. But the parameters you included are added and work fine, so it has to be Neptune's orbit.

[selden]

ou8poop2,

What xyz file are you using for Voyager 2's trajectory?

Remember that Celestia only does a linear interpolation between adjacent trajectory samples. Whenever a spacecraft's path is changing quickly, as for the Voyager flyby of Neptune, one has to be careful to use samples that are very close to one another. Otherwise you can be mislead as Celestia follows the straight line between samples that are on either side of a major path change.

Using a fine-grained trajectory (~15 minute steps) for Voyager 2, I get a closest approach to Grant's elliptical orbit elements for Triton of about 38,700 km at about 1989 08 25 09:14 utc. At that time, the distance between Triton's positions as defined by Grant's elliptical elements and by Horizon's helipcentric cartesian coordinates is about 12,000 km, which seems reasonably good to me.

The trajectory files that I used are available at http://www.lns.cornell.edu/~seb/celestia/spacecraft.html#3.4.10. I also used Grant's solarsys.ssc and triton-v2.ssc files which are available athttp://www.lns.cornell.edu/~seb/celestia/hutchison/index.html

[ou8poop2]

yes, i think that fixed it
i was able to reproduce the encounter, using those ssc and xyz files. i know how to change the texture to the correct images (instead of the the supplied saturn.jpg)
what i am wondering is would anyone know how to correct the orbital info in the main solarsys.scc? in an overhead position, with the sun shining from the top of the screen, i see the neptune ane neptune-v2-xyz images overlapping; not too bad, though. But triton is sitting at the 9 o clock position while triton-v2-xyz is sitting at 7 o clock. so, does anyone have in their solarsys.ssc triton's orbital info that gets it anywhere CLOSE to where the voyager 2 encounter took place without using an xyz for triton itself?
ps, thank you very much Selden, at least i get to see two Tritons.

[selden]

ou8poop2,

The correct cure will have to wait until a future major release of Celestia (probably not 1.2.5, which is due out RSN ) when Celestia uses a multi-term CustomOrbit formula for Triton's orbit. In the near term, however, Grant Hutchison has created an EllipticalOrbit definition which is reasoably good. See his Web page at http://www.lns.cornell.edu/~seb/celestia/hutchison. It is not yet included in his modified version of solarsys.ssc on that page. It doesn't quite agree with the xyz trajectory, so now you'll have 3 Tritons on screen!

[granthutchison]

Grant, maybe you could post your scc info for neptune as well. mine seems a bit skewed, because when i add your triton info in, im still 207,000 km from it at Voyager's closest approach. I probably either have old data, or screwed it up along the way somehow. But the parameters you included are added and work fine, so it has to be Neptune's orbit.

Selden seems to have sorted this out for you while I wasn't looking - sorry.
You're right: the problem you had lay with the orientation of Neptune - the pole points in the wrong direction in the solarsys.ssc that comes with Celestia. So my revised elements for Triton above need to be combined with my revised solarsys.ssc that Selden pointed you at, which sorts the Neptune orientation.
I'm trying to batch these various corrections and consolidate them into my revised solarsys.ssc - the next revision will correct the ascending node errors for the various satellites that are still defined by elliptical orbits (including Triton, as above), and that should be posted very soon.

Grant

[ou8poop2]

LOL
THREE Tritons?! My world couldn't get any better!
That's okay, not rushing anyone: there a lot of things now that need attention, and im happy for now to have a reasonable fix.
My thanks to both, Selden and Grant - keep up the great work!

[JackHiggins]

I can beat that- ive got 5 tritons now all with different elements and NONE of them seem to work properly!!! the closest i get is about 2 million km (just a tad off) I think il wait until this is all sorted out & get all the updates then... (or wait for 1.2.5 when its finished!)

[granthutchison]

I can beat that- ive got 5 tritons now all with different elements and NONE of them seem to work properly!!! the closest i get is about 2 million km (just a tad off) I think il wait until this is all sorted out & get all the updates then... (or wait for 1.2.5 when its finished!)

My revised solarsys.ssc and new textures at
http://www.lns.cornell.edu/~seb/celestia/hutchison/
now contains the whole works in one package - corrections to Neptune's orientation, Triton's orbit and Triton's orientation. If you use that, ditch all your other Triton definitions (six is just too many Tritons for one solar system ), and plug in the Voyager 2 xyz data from Selden, you should see a pretty good encounter.

Grant

[billybob884]

instead of putting up a whole new solarsys.ssc, why dont you just post a list of code to add/replace in the solarsys.ssc for those that have made their own "ajustments"

[granthutchison]

instead of putting up a whole new solarsys.ssc, why dont you just post a list of code to add/replace in the solarsys.ssc for those that have made their own "ajustments"

Well, there's now an alteration to almost every body in solarsys.ssc except Earth, Moon and asteroids - so one is pretty much the equivalent of the other. But here goes:

Code: Select all

# Data for our solar system.

#Revisions by Grant Hutchison December 2002:
#Correct orientation of axes and prime meridians for all planets
#Appropriate position of prime meridians for all synchronous satellites
#Re-orientation of some maps, to place prime meridian in the centre
#Addition of IAU grids as optional maps
#Addition of Venus surface map from USGS and Hyperion surface map by Phil Stooke, both public domain
#Original venus.jpg rotated to orientate cloud patterns correctly, and used as a CloudMap

"Mercury" "Sol"
{
   Texture "mercury.jpg"
   #Texture "westgrid.jpg" #added IAU grid texture map
   BumpMap "mercurybump.jpg"
   BumpHeight 2.5
   Radius 2440

   CustomOrbit "vsop87-mercury"
   EllipticalOrbit {
   Period            0.2408
   SemiMajorAxis     0.3871
   Eccentricity      0.2056
   Inclination       7.0049
   AscendingNode    48.33167
   LongOfPericenter 77.456
        MeanLongitude   252.251
   }

   RotationPeriod 1407.509405 #revised value
   Obliquity   7.01
   EquatorAscendingNode 48.42 #revised value

   RotationOffset   291.20 #correct orientation for map with central prime meridian

   Albedo            0.06
}

"Venus" "Sol"
{
   Texture "venussurfacerotate.jpg" #added surface map with central prime meridian and correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   HazeColor [ 0.5 0.35 0.2 ]
   HazeDensity 0.35
   Radius 6052

   Atmosphere {
      Height 60
      Lower [ 0.8 0.8 0.5 ]
      Upper [ 0.6 0.6 0.6 ]
      Sky [ 0.8 0.8 0.5 ]
      CloudMap "venuscloudsrotate.jpg" #rotated venus.jpg, to orientate cloud patterns correctly
      CloudHeight 50 #height of densest cloud layer
      CloudSpeed  90 #clouds super-rotate - one rotation in 4 days
   }

   CustomOrbit "vsop87-venus"
   EllipticalOrbit {
      Period            0.6152
      SemiMajorAxis     0.7233
      Eccentricity      0.0068
      Inclination       3.3947
      AscendingNode     76.681
      LongOfPericenter 131.533
           MeanLongitude    181.979
   }

   RotationPeriod  5832.479839 #revised value
   Obliquity   178.78 #revised value
   EquatorAscendingNode 300.22 #revised value


   RotationOffset   137.45 #correct orientation for map with central prime meridian

   Albedo            0.77
}

"Mars" "Sol"
{
   Texture "mars180.jpg" #revised texture map with central prime meridian
   #Texture "westgrid.jpg" #added IAU grid texture map
   BumpMap  "marsbump180.jpg" #revised bump map with central prime meridian
   BumpHeight 2.5
   Color   [ 1 0.75 0.7 ]
   HazeColor [ 1 1 1 ]
   HazeDensity 0.45
   Radius 3394
   # Oblateness 0.006

   Atmosphere {
      Height 30
      Lower [ 0.8 0.6 0.6 ]
      Upper [ 0.7 0.3 0.3 ]
      Sky [ 0.83 0.75 0.65 ]
   }

   CustomOrbit "vsop87-mars"
   EllipticalOrbit
   {
   Period            1.8809
   SemiMajorAxis     1.5237
   Eccentricity      0.0934
   Inclination       1.8506
   AscendingNode     49.479
   LongOfPericenter 336.041
        MeanLongitude    355.453
   }

   RotationPeriod    24.622962
   Obliquity   26.72 #revised value
   EquatorAscendingNode 82.91 #revised value

   RotationOffset 136.005 #correct orientation for map with central prime meridian
   
   Albedo            0.150
}

"Phobos" "Sol/Mars"
{
   Mesh "phobos.3ds"
   Texture "phobosmirror.jpg" #revised texture map to bring features into correct position
   #Texture "westgridmirror.jpg" #added IAU grid texture map
   Radius 11

   EllipticalOrbit
   {
   Period         0.31891023 #mean value
   SemiMajorAxis  9377.2 #mean value
   Eccentricity   0.0151 #mean value
        Inclination    1.075 #mean value
        AscendingNode  128.694 #at epoch J2000.0
   ArgOfPericenter 213.804 #at epoch J2000.0
        MeanAnomaly    191.771 #at epoch J2000.0
   }

   Obliquity      1.075 #normal to orbit
        EquatorAscendingNode 128.694 #correct orientation for given ascending node
   RotationOffset 45.575  #correct orientation map with central prime meridian

   Albedo         0.07
}

"Deimos" "Sol/Mars"
{
   Mesh "deimos.3ds"
   Texture "deimosmirror.jpg" #revised texture map to bring features into correct position
   #Texture "westgridmirror.jpg" #added IAU grid texture map
   Radius 6

   EllipticalOrbit
   {
   Period      1.2624407 #mean value
   SemiMajorAxis   23463.2 #mean value
   Eccentricity   0.00033 #mean value
   Inclination   1.791 #mean value
   AscendingNode   25.229 #at epoch J2000.0
   ArgOfPericenter   208.213 #at epoch J2000.0
   MeanAnomaly   344.128 #at epoch J2000.0
   }

   Obliquity      1.791 #normal to orbit
   EquatorAscendingNode 25.229 #correct orientation for given ascending node
   RotationOffset 192.341 #correct orientation map with central prime meridian

   Albedo         0.08
}

"Jupiter" "Sol"
{
   Texture "jupiter.jpg"
   #Texture "westgrid.jpg" #added IAU grid texture map
   HazeColor [ 0.4 0.45 0.5 ]
   HazeDensity 0.3

   Radius 71398
   Oblateness 0.064

   CustomOrbit "vsop87-jupiter"
   EllipticalOrbit
   {
   Period           11.8622
   SemiMajorAxis     5.2034
   Eccentricity      0.0484
   Inclination       1.3053
   AscendingNode   100.556
   LongOfPericenter 14.7539
        MeanLongitude    34.404
   }

   RotationPeriod    9.924920 #revised value: System III - magnetic field
   Obliquity   2.22 #revised value
   EquatorAscendingNode   337.77 #revised value

   RotationOffset 305.40 #correct orientation for map with central prime meridian

   Albedo            0.51
}


"Amalthea" "Sol/Jupiter"
{
   Texture "asteroid.jpg"
   #Texture "westgridmirror.jpg" #added IAU grid texture map
   BlendTexture true
   Color   [ 0.5 0.12 0.16 ]
   Mesh "amalthea.3ds"
   Radius    124

   EllipticalOrbit
   {
   Epoch         2452583.763194445 #2002 Nov 05.26 (Galileo encounter)
   Period      0.49817905 #revised to mean value
   SemiMajorAxis   181994.98
   Eccentricity    0.0046637841
   Inclination     0.39217201
   AscendingNode   224.4139186 #revised value
   ArgOfPericenter 293.4707817
   MeanAnomaly     319.3794140
   }
   
   Obliquity   0.4 #axis normal to orbit
   EquatorAscendingNode 224.41 #correct orientation for given ascending node
   RotationOffset   209.583 #correct orientation for given orbital parameters

   Albedo          0.06
}

"Io" "Sol/Jupiter"
{
   Texture "io180.jpg" #revised texture map with central prime meridian
   #Texture "westgrid.jpg" #added IAU grid texture map
   Radius   1821

   CustomOrbit "io"
   EllipticalOrbit
   {
   Epoch 2443000.00038375
   Period         1.769138
   SemiMajorAxis  421600
   Eccentricity   0.0041
   Inclination    0.040
   AscendingNode    312.981
   LongOfPericenter  97.735
   MeanLongitude    106.724
   }

        RotationOffset 198 #correct orientation for map with central prime meridian

   Albedo         0.61
}

"Europa" "Sol/Jupiter"
{
   Texture "europa180.jpg" #revised texture map with central prime meridian
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius   1565

   CustomOrbit "europa"
   EllipticalOrbit
   {
   Epoch 2443000.00038375
   Period         3.551810
   SemiMajorAxis  670900
   Eccentricity   0.0101
   Inclination    0.470
   AscendingNode    101.087
   LongOfPericenter 155.512
   MeanLongitude    176.377
   }

   RotationPeriod 85.22834590 #corrects synchronization error in current Celestia
   RotationOffset 32 #correct orientation for map with central prime meridian
   Albedo         0.64
}

"Ganymede" "Sol/Jupiter"
{
   Texture "ganymede180.jpg" #revised texture map with central prime meridian
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius   2634

   CustomOrbit "ganymede"
   EllipticalOrbit
   {
   Epoch 2443000.00038375
   Period         7.154553
   SemiMajorAxis  1070000
   Eccentricity   0.0015
   Inclination    0.195
   AscendingNode    119.841
   LongOfPericenter 188.831
   MeanLongitude    121.206
   }

   RotationOffset 40 #correct orientation for map with central prime meridian

   Albedo         0.42
}


"Callisto" "Sol/Jupiter"
{
   Texture "callisto150.jpg" #revised texture map with central prime meridian
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius   2403

   CustomOrbit "callisto"
   EllipticalOrbit
   {
   Epoch 2443000.00038375
   Period        16.689018
   SemiMajorAxis  1883000
   Eccentricity   0.007
   Inclination    0.281
   AscendingNode    323.265
   LongOfPericenter 335.933
   MeanLongitude     85.091
   }

        RotationOffset 260 #correct orientation for map with central prime meridian

   Albedo         0.20
}


"Saturn" "Sol"
{
   Texture "saturn.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Color [ 1.0 1.0 0.85 ]
   HazeColor [ 0.0 0.0 1 ]
   HazeDensity 0.25
   Radius 60330
   Oblateness 0.1076

   CustomOrbit "vsop87-saturn"
   EllipticalOrbit
   {
   Period           29.4577
   SemiMajorAxis     9.5371
   Eccentricity      0.0542
   Inclination       2.4845
   AscendingNode   113.715
   LongOfPericenter 92.432
        MeanLongitude    49.944
   }

   RotationPeriod      10.656222 #System III - magnetic field
   Obliquity           28.052
   EquatorAscendingNode  169.53 #revised value

   RotationOffset   358.922 #correct orientation for map with central prime meridian

   Albedo            0.50

   Rings {
      Inner   74658
      Outer  140000
      Texture "saturn-rings.png"

      # Bjorn Jonsson <http://www.mmedia.is/~bjj> recommends this
      # color for rendering Saturn's rings.  No idea if it's right,
      # but it looks nice
      Color  [ 1.0 0.88 0.82 ]
   }
}

"Mimas" "Sol/Saturn"
{
   Texture "mimas.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   BlendTexture true
   Color [ 0.75 0.63 0.58 ]
   Radius    199

   CustomOrbit "mimas"
   EllipticalOrbit
   {
   Period         0.9424218
   SemiMajorAxis  185520
   Eccentricity   0.0202
   Inclination    1.53
   MeanAnomaly   23
   }

   RotationOffset 330 #correct orientation for map with central prime meridian

   Albedo         0.5
}

"Enceladus" "Sol/Saturn"
{
   Texture "asteroid.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius     249

   CustomOrbit "enceladus"
   EllipticalOrbit
   {
   Period         1.370218
   SemiMajorAxis  238020
   Eccentricity   0.0045
   Inclination    0.02
   MeanAnomaly    215
   }

   RotationOffset 320 #correct orientation for map with central prime meridian

   Albedo         0.99
}

"Tethys" "Sol/Saturn"
{
   Texture "tethys.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius     530

   CustomOrbit "tethys"
   EllipticalOrbit
   {
   Period         1.887802
   SemiMajorAxis  294660
   Eccentricity   0.0
   Inclination    1.09
   MeanAnomaly    98
   }

   RotationOffset 325 #correct orientation for map with central prime meridian

   Albedo         0.9
}

"Dione" "Sol/Saturn"
{
   Texture "dione.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius     560

   CustomOrbit "dione"
   EllipticalOrbit
   {
   Period         2.736915
   SemiMajorAxis  377400
   Eccentricity   0.0022
   Inclination    0.02
   MeanAnomaly    310
   }

   RotationOffset 315 #correct orientation for map with central prime meridian

   Albedo         0.7
}

"Rhea" "Sol/Saturn"
{
   Texture "rhea.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius     764

   CustomOrbit "rhea"
   EllipticalOrbit
   {
   Period         4.517500
   SemiMajorAxis  527040
   Eccentricity   0.0010
   Inclination    0.35
   MeanAnomaly    190
   }

   RotationOffset 190 #correct orientation for map with central prime meridian

   Albedo         0.7
}

"Titan" "Sol/Saturn"
{
   Texture "titan.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Color [ 1.0 0.9 0.75 ]
   HazeColor [ 0.2 0.5 1 ]
   HazeDensity 1
   Radius   2575

   Atmosphere {
      Height 60
      Lower [ 0.8 0.4 0.1 ]
      Upper [ 0.0 0.0 0.9 ]
      Sky [ 0.8 0.4 0.1 ]
   }

   CustomOrbit "titan"
   EllipticalOrbit
   {
   Period        15.945421
   SemiMajorAxis  1221850
   Eccentricity   0.0292
   Inclination    0.33
   MeanAnomaly    120
   }


   RotationPeriod 382.69074184 #corrects synchronization error in current Celestia
   RotationOffset 145 #correct orientation for map with central prime meridian

   Albedo         0.21
}

"Hyperion" "Sol/Saturn"
{
   Mesh "hyperion.3ds"
   #Texture "asteroid.jpg"
   Texture "hyperionmirror.jpg" #added surface map by Phil Stooke, re-orientated to bring features into correct position
   #Texture "westgridmirror.jpg" #added IAU grid texture map

   Radius   205

   CustomOrbit "hyperion"
   EllipticalOrbit
   {
   Period        21.276609
   SemiMajorAxis  1481100
   Eccentricity   0.1042
   Inclination    0.43
   MeanAnomaly    350
   }

   # The rotation of Hyperion is chaotic; we don't attempt to model
   # the rotation exactly, but instead use non-zero precession rate to
   # make the rotation appear somewhat irregular.
   Obliquity       25
   RotationPeriod  336 # 13 days
   PrecessionRate  15.65 # 23 days

   Albedo         0.3
}

"Iapetus" "Sol/Saturn"
{
   Texture "iapetus.jpg"
   #Texture "westgrid.jpg"#added IAU grid texture map
   Radius     718

   CustomOrbit "iapetus"
   EllipticalOrbit
   {
   Period         79.330183
   SemiMajorAxis  3561300
   Eccentricity   0.0283
   Inclination    7.52
   MeanAnomaly    245
   }

   RotationOffset 230 #correct orientation for map with central prime meridian

   Albedo         0.2
}

"Uranus" "Sol"
{
   Texture "uranus.jpg"
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Color [ 0.75 0.85 1.0 ]
   HazeColor [ 0.5 0.8 1.0 ]
   HazeDensity 0.2
   Radius 26200
   Oblateness 0.024

   CustomOrbit "vsop87-uranus"
   EllipticalOrbit
   {
   Period           84.0139

   SemiMajorAxis    19.1913
   Eccentricity      0.0472
   Inclination       0.7699
   AscendingNode     74.230
   LongOfPericenter 170.964
        MeanLongitude    313.232
   }

   RotationPeriod   17.24 #System III - magnetic field
   Obliquity   97.81 #revised value
   EquatorAscendingNode 167.76

   RotationOffset   -28.82 #correct orientation for map with central prime meridian   
   
   Albedo            0.66

   Rings {
      Inner  41800
      Outer  51149
      Texture "uranus-rings.png"
   }
}

"Miranda" "Sol/Uranus"
{
   Texture "miranda90rotate.jpg" #revised texture map with central prime meridian and correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   235

   CustomOrbit "miranda"
   EllipticalOrbit
   {
   Period         1.413
   SemiMajorAxis  129800
   Eccentricity   0.0027
   Inclination    4.22
   MeanAnomaly    120
   }

   RotationPeriod 33.92350159 #corrects synchronization error in current Celestia
   RotationOffset 330 #correct orientation for map with central prime meridian
}

"Ariel" "Sol/Uranus"
{
   Texture "arielrotate.jpg" #revised texture map with correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   576

   CustomOrbit "ariel"
   EllipticalOrbit
   {
   Period         2.520
   SemiMajorAxis  191200
   Eccentricity   0.0034
   Inclination    0.31
   MeanAnomaly    56
   }

   RotationPeriod 60.48909292 #corrects synchronization error in current Celestia
   RotationOffset 200 #correct orientation for map with central prime meridian
}

"Umbriel" "Sol/Uranus"
{
   Texture "umbrielrotate.jpg" #revised texture map with correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   585

   CustomOrbit "umbriel"
   EllipticalOrbit
   {
   Period         4.144
   SemiMajorAxis  266000
   Eccentricity   0.0050
   Inclination    0.36
   MeanAnomaly    280
   }

   RotationPeriod 99.46022991 #corrects synchronization error in current Celestia
   RotationOffset 250 #correct orientation for map with central prime meridian
}

"Titania" "Sol/Uranus"
{
   Texture "titaniarotate.jpg" #revised texture map with correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   789

   CustomOrbit "titania"

   EllipticalOrbit
   {
   Period         8.706
   SemiMajorAxis  435800
   Eccentricity   0.0022
   Inclination    0.10
   MeanAnomaly    30
   }

   RotationPeriod 208.94077099 #corrects synchronization error in current Celestia
   RotationOffset 280 #correct orientation for map with central prime meridian
}

"Oberon" "Sol/Uranus"
{
   Texture "oberonrotate.jpg" #revised texture map with correct orientation
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   761

   CustomOrbit "oberon"
   EllipticalOrbit
   {
   Period        13.463
   SemiMajorAxis  583600
   Eccentricity   0.0008
   Inclination    0.10
   MeanAnomaly    150
   }

   RotationPeriod 323.117567539 #corrects synchronization error in current Celestia
   RotationOffset 350 #correct orientation for map with central prime meridian   
}


"Neptune" "Sol"
{
   Texture "neptune.jpg"
   #Texture "westgrid.jpg" #added IAU grid texture map
   Color [ 0.75 0.75 1.0 ]
   HazeColor [ 0.6 1 0.75 ]
   HazeDensity 0.35
   Radius 25225
   Oblateness 0.027

   CustomOrbit "vsop87-neptune"
   EllipticalOrbit
   {
   Period           164.793
   SemiMajorAxis     30.0690
   Eccentricity      0.0086
   Inclination       1.7692
   AscendingNode   131.722
   LongOfPericenter 44.971
        MeanLongitude   304.880
   }

   RotationPeriod   16.11 #System III - magnetic field
   Obliquity        28.03
   EquatorAscendingNode 49.24 #revised value

   RotationOffset   228.65 #correct orientation for map with central prime meridian

   Albedo            0.62
}

"Proteus" "Sol/Neptune"
{
   Mesh "proteus.3ds"
   Texture "asteroid.jpg"
   #Texture "westgridmirror.jpg" #added IAU grid texture map
   Radius   218

   EllipticalOrbit
   {
   Epoch      2450085.5 #revised value - 1996 Jan 03.0 (earliest Horizons data)
   Period      1.122315  #revised to mean value
   SemiMajorAxis   117600    #revised to mean value
   Eccentricity   0.0004    #revised to mean value
   Inclination   1.101     #revised value - at epoch
   AscendingNode   327.378   #revised value - at epoch
   ArgOfPericenter   277.888   #revised value - at epoch
   MeanAnomaly   206.367   #revised value - at epoch
   }

   Obliquity      1.1 #normal to orbit
   EquatorAscendingNode 327.378 #correct orientation for given ascending node
   RotationOffset 281.590 #correct orientation for map with central prime meridian

   Albedo         0.2
}

"Triton" "Sol/Neptune"
{
   Texture "triton.jpg"
   #Texture "eastgrid.jpg"
   Radius   1353

   Atmosphere {
      Height 1
      Lower [ 0.5 0.5 0.5 ]
      Upper [ 0.5 0.5 0.5 ]
      Sky [ 0.0 0.0 0.0 ]
   }

   EllipticalOrbit
   {
   Epoch      2447763.5 #revised value - 1989 Aug 25.00 (Voyager encounter)
   Period      5.8768541 #revised to mean value
   SemiMajorAxis   354765.286 #revised value - at epoch
   Eccentricity   0.000022849 #revised value - at epoch
   Inclination   156.826240 #revised value - at epoch
   #AscendingNode   172.426656 #revised value - at epoch
   AscendingNode   147.899288 #revised value - at epoch
   ArgOfPericenter   293.092400 #revised value - at epoch
   MeanAnomaly   315.726316 #revised value - at epoch
   }

   Obliquity   23.174  #normal to orbit
   EquatorAscendingNode   327.899 #correct orientation for given ascending node
   RotationOffset   -53.161 #correct orientation for map with central prime meridian

   RotationPeriod   -141.0444984 #correct retrograde rotation

   Albedo         0.7
}

"Nereid" "Sol/Neptune"
{
   Mesh "asteroid.cms"
   Texture "asteroid.jpg"
   #Texture "westgrid.jpg" #added IAU grid texture map
   Radius   170

   EllipticalOrbit
   {
   Epoch      2447763.5 #revised value - 1989 Aug 25.00 (Voyager encounter)
   Period      360.13619 #revised to mean value
   SemiMajorAxis   5513400   #revised to mean value
   Eccentricity   0.7512    #revised to mean value
   Inclination   28.385    #revised value - at epoch
   AscendingNode   190.678   #revised value - at epoch
   ArgOfPericenter 17.690    #revised value - at epoch
   MeanAnomaly       36.056    #revised value - at epoch
   }
}


"Pluto" "Sol"
{
   Texture "pluto.jpg"
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   BumpMap "plutobump1k.jpg"
   BumpHeight 2.5
   Radius 1137

   CustomOrbit "pluto"
   EllipticalOrbit
   {
   Period            248.54
   SemiMajorAxis     39.48168677
   Eccentricity       0.24880766
   Inclination       17.14175
   AscendingNode    110.30347
   LongOfPericenter 224.06776
   MeanLongitude    238.92881
   }

   RotationPeriod  153.293904 #revised value
   Obliquity      115.604 #revised value
   EquatorAscendingNode   228.335 #revised value

   RotationOffset  -39.25 #correct orientation for map with central prime meridian

   Albedo            0.3
}

"Charon" "Sol/Pluto"
{
   Texture "charon.jpg"
   #Texture "eastgridrotate.jpg" #added IAU grid texture map
   Radius   593

   InfoURL "http://www.nineplanets.org/pluto.html#Charon"

   EllipticalOrbit
   {
   Period         6.387246 #revised value
   SemiMajorAxis  19636
   Eccentricity   0.0076
   Inclination    0.0 # 96.163 degrees relative to ecliptic
   MeanAnomaly    -39.254 #revised value for correct orientation
   }
   
   RotationOffset  140.75 #correct orientation for map with central prime meridian

   Albedo         0.3
}


The revised values are commented so you can pick out what you like.
To get the revised textures that go with these modifications, you'll need to download the newtextures.zip file from Selden's website at
http://www.lns.cornell.edu/~seb/celestia/hutchison

If you want to preserve your own solarsys.ssc changes, be sure to unzip newtextures.zip into a temporary directory, and then copy the new textures across to the medres and lores directories in Celestia. Otherwise the unzipped file will try to drop my new solarsys.ssc on top of your personal version .

One thing I haven't incorporated above is the correct position of the Great Red Spot on Jupiter, because it's very dependent on the texture you're using. If you're interested in getting the appearance of Jupiter correct in this respect, see my recent post on another thread
http://www.shatters.net/forum/viewtopic.php?t=1497

I should also tell you that my corrections to Jupiter's orientation at present undo some ad hoc corrections made by Chris. The orbits of the Galilean satellites of Jupiter in 1.2.5pre7 are torqued by ~20 degrees. Chris had temporarily inserted an opposite jigger factor in the orientation of Jupiter while he sorts out the problem, to give a better appearance in the satellite positions. The whole thing should be fixed in the next release.

Grant