the next thing to do is to start using spice
There are a few different ways to do this

( and a bit of time to wrap ones brain around 3d geometry in space )

i am using the SSB ( Solar System Barycenter ) locations and planet/moon barycenters relative to the ssb

see the wikibook page :
http://en.wikibooks.org/wiki/Celestia/SPICE
-- note this needs to be updated

-- links
-- the "c" docs
http://naif.jpl.nasa.gov/pub/naif/toolk ... index.html
-- a good PDF on the spk kernels
http://naif.jpl.nasa.gov/pub/naif/toolk ... 19_spk.pdf
-- general tutorials
http://naif.jpl.nasa.gov/naif/tutorials.html
http://naif.jpl.nasa.gov/naif/gettinghelp.html
-- programming with spice
http://naif.jpl.nasa.gov/naif/lessons.html

For general information wikipedia is not that bad of a source .
but a few more will be needed


The "de438.bsp" file needs to be downloaded and installed to
celestia/extras/data ( or your custom "extras" folder defined in the " celestia.cfg " file )
----
ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/de438.bsp
----
before planets and moons and spacecraft can be added the Barycenter's need to be defined in an ssc file


as you might have noticed in the ssc file I am using the smaller "de438.bsp"( 114.2 Meg) instead of the HUGE 3.2 Gig "de431.bsp"
de438 covers the time frame from "1549 DEC 31 to 2650 JAN 25"
de431 covers the time frame from "13201 B.C. to 17191 A.D."
see the readme file
ftp://naif.jpl.nasa.gov/pub/naif/generi ... t_SPKs.txt

the bsp files are the "when and where ( position/velocity) " location "Spice kernels"
and they are in the PDS "generic_kernels" archive located here:
ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels/
all the planets and moons are here , well most of them , some are in the mission specific archives .

but for the barycenters we only need the one in the "spk" section for the planets
-- the readme for the "spk" section
ftp://naif.jpl.nasa.gov/pub/naif/generi ... E_SPKs.txt

Download " de438.bsp "
ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/

--- pdf warning -- spice doc/tutorial on the spk files
http://naif.jpl.nasa.gov/pub/naif/toolk ... 19_spk.pdf

now this is where using cspice programs come in
notice the "Beginning" and "Ending" times



well if you are scratching your head trying to figure out how these are determined this please read the tutorial on using cspice
and see the user guide:
http://naif.jpl.nasa.gov/pub/naif/toolk ... index.html

the program called "brief"
open a terminal in the folder that has the bsp file and run

the output will be this


or from the "brief --help" menu use the "-t" option instead of the "-c" option

same data but a different format


on to the meat of the ssc file
i am going to use Earth as an example


this is rather self explanatory
"Beginning and Ending"
are the times from the bsp file BUT the month is NOT using letters !!!
But the number for the month

"OrbitFrame " is using EclipticJ2000 frame

two odd ones are
----
Visible true
Clickable true
----
this is overiding the celestia default orbits SO
if you want to see the orbit and be able to click on the body for this orbit ,these need to be set to "true"


"Kernel"
the name of the one being used

"Target"
this is the numeral from the output of "brief" for the body
this will NEVER change
1 will ALWAYS be the barycenter for Mercury
3 will ALWAYS be the barycenter for the Earth

"Origin"
this is the SUN barycenter "0"
( for a moon of Jupiter it will be "5" for Jupiter
all bodies are relative to the parent body

" Period"
This is the length of a year and is in earth years


---- INSTALLING ----

For MS windows 7
C:\\Celestia\extras\Barycenter.ssc
( Celestia NEEDS TO BE installed here C:\\Celestia , this is do to the FUBAR mess Microsoft made with the UAC )

For Linux
/Your.Celestia.Install.Location/celestia/extras/1.Barycenter.ssc
/usr/share/celestia/extras
/DATA/SUSE12/Celestia.svn/extras

gcc enforces the c langguage read order so the ssc DOSE need that 1. in front so that it is read FIRST before the ssc for the planets
( SolarSystem.SPICE.ssc )
the naming is very important !!!
any ssc file that NEEDS a ssecond ssc file MUST 100% MUST be read AFTER the file it needs !!!!!
the barycenter ssc MUST be read BEFORE the ssc for the planets
( this is the same issue as with reading "SomeLibrary.so's" from a list )

-- an update

the barycenter kernel has been updated to the "de436.bsp"
ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/de436.bsp

now the times have remained the same so just a minor edit

the ssc in a zip file is here
https://drive.google.com/open?id=0B6ZYA ... kd1aUJYSHc

_________________
"I don't pitch Linux to my friends, I let Microsoft do that for me."
Using OpenSUSE 42.1 & Scientific Linux 6.7

--- update --

De438.bsp was released in May of 2018
ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/

the above files are being edited to use it

_________________
"I don't pitch Linux to my friends, I let Microsoft do that for me."
Using OpenSUSE 42.1 & Scientific Linux 6.7