To display a comet or asteroid in Celestia, use your favorite text editor to create a file with the filetype ".ssc" in Celestia's "extras" folder. In it you need to specify the object's name and its orbital parameters.
The International Astronomical Union publishes circulars which have orbital elements for comets and for asteroids. This is a brief, incomplete, description of how to transform the IAU orbital elements of a comet or asteroid into Celestia's SSC format.
Cometary Orbital Elements | ||
---|---|---|
Element name or symbol | Celestia SSC keyword | Description |
Epoch | Epoch (1,2) | Julian date when elements are valid |
e or Ecc | Eccentricity | Elongation of ellipse: 0.0 = circle, 1.0 = parabola, .gt. 1.0 = hyperbola (pure number) |
q | PericenterDistance | Closest approach to Sun (in AU) |
T or Tp | Epoch (1,2) | Time of PeriCenter passage (Julian date) |
Node or W or Ω | AscendingNode | Where the Orbit crosses the Ecliptic (longitude, in degrees) |
Peri or w or ω | ArgOfPericenter | angle from "Node" to Pericenter (in degrees) |
Incl or i | Inclination | Tilt of orbit from Ecliptic (in degrees) |
(not provided) | Period | calculated orbital
period (in Earth years), using either
P = (q/(1-e))^1.5 for a closed, elliptical orbit P = (q/(e-1))^1.5 for an open, hyperbolic orbit Unfortunately, P is undefined for a parabolic orbit. |
C/1995 O1 (Hale-Bopp) Epoch 1997 Mar. 13.0 TT = JDT 2450520.5 T 1997 Apr. 1.1373 TT Nakano q 0.914142 (2000.0) P Q z +0.005395 Peri. 130.5887 -0.1331204 -0.1703043 Node 282.4707 +0.2822928 +0.9378055 e 0.995068 Incl. 89.4300 +0.9500472 -0.3025183 From 3000 observations 1993 Apr. 27-2001 Feb. 17, mean residual 0".8. Nongravitational parameters A1 = +1.27, A2 = +0.1144.
Note that Celestia does not properly handle object names which include
a "/". That character is used by Celestia as a separator between object
names. As a result, a name which contains a "/" cannot be defined to
have a satellite, nor can it be selected by typing a
[carriage-return]
followed by the name of the object.
Otherwise such a name is OK: the name can be selected using Celestia's
"Solar System Browser", for example.
Celestia ignores anything starting with a #, so everything on a line after a # is a comment meant only for your information.
#C/1995 01 Hale-Bopp (CfA) # "name of object" "name of primary" "Hale-Bopp" "Sol" { Class "comet" Texture "asteroid.jpg" Mesh "asteroid.cms" Radius 20.0 # arbitrary RotationPeriod 11.34 # arbitrary # taken from # http://cfa-www.harvard.edu/iau/Ephemerides/Comets/1995O1.html EllipticalOrbit { Period 2523.363 #calculated: (q/(1-e))**1.5 PericenterDistance 0.914142 # q Eccentricity 0.995068 # e Inclination 89.4300 # Incl. AscendingNode 282.4707 # Node ArgOfPericenter 130.5887 # Peri. MeanAnomaly 0.0 # position at T Epoch 2450539.6373 # T } InfoURL "http://www.jpl.nasa.gov/comet/" }
Asteroidal (Minor Planet) Orbital Elements | ||
---|---|---|
Element name or symbol | Celestia SSC keyword | Description |
a = (q+Q)/2 | SemiMajorAxis | half of the length of the long axis of an ellipse |
Epoch | Epoch | Date when elements are valid |
e or Ecc | Eccentricity | Elongation of ellipse: 0.0 = circle, 1.0 = parabola |
Node or W or Ω | AscendingNode | Where the Orbit crosses the Ecliptic |
Peri or w or ω | ArgOfPericenter | angle from "Node" to Pericenter |
Incl or i | Inclination | Tilt of orbit from Ecliptic |
M | MeanAnomaly | The location of the body in the orbit at the specified Epoch |
P = a^1.5 = sqrt(a^3) | Period | time for object to revolve around the Sun |
q | PericenterDistance | Closest approach to Sun |
Q (1) | (not used) | apocenter: greatest distance from the Sun |
Orbital elements: 1998 FL5 Epoch 1998 Mar. 8.0 TT = JDT 2450880.5 Williams M 22.37287 (2000.0) P Q n 0.51950119 Peri. 297.40999 -0.54744251 -0.83644649 a 1.5325395 Node 185.97874 +0.82823536 -0.53714947 e 0.3601172 Incl. 14.32281 +0.11971998 -0.10875532 P 1.90 H 21.0 G 0.15
"1998 FL5" "Sol" { Class "asteroid" Texture "asteroid.jpg" Mesh "asteroid.cms" Radius 270.0 # table lookup using H EllipticalOrbit { Period 1.90 # P SemiMajorAxis 1.5325395 # a Eccentricity 0.3601172 # e Inclination 14.32281 # Incl. AscendingNode 185.97874 # Node ArgOfPericenter 297.40999 # Peri. MeanAnomaly 22.37287 # M Epoch 2450880.5 # Epoch } InfoURL "http://cfa-www.harvard.edu/mpec/J98/J98F20.html" }
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