Help with ephemeris

[ShortTermParking]

Hi,
I have here an ephemeris of a comet from nasa, and I just want to know how to put it into an addon for celestia. It's the NEAT comet, and here is the ephemeris:

C/2002 V1 (NEAT)
Epoch 2003 Feb. 10.0 TT = JDT 2452680.5
T 2003 Feb. 18.2960 TT MPCM
q 0.099265 (2000.0) P Q
z +0.000877 Peri. 152.1677 -0.4469489 -0.0894116
+/-0.000007 Node 64.0880 -0.8865844 -0.0882906
e 0.999913 Incl. 81.7153 +0.1191842 -0.9920738
From 1391 observations 2002 Nov. 6-2003 Feb. 9, mean residual 0".6.

Elements are also available for the current standard epoch:
C/2002 V1 (NEAT)
Epoch 2002 Nov. 22.0 TT = JDT 2452600.5
T 2003 Feb. 18.2967 TT MPCM
q 0.099265 (2000.0) P Q
z +0.000920 Peri. 152.1682 -0.4469364 -0.0894322
+/-0.000007 Node 64.0880 -0.8865919 -0.0882705
e 0.999909 Incl. 81.7171 +0.1191750 -0.9920737


I'm not an astronomer, so I have no clue what most of this stuff means. Can someone give me a hand? Has someone already added this?

Thanx,
Thomas

[JackHiggins]

Ok heres what each of the terms that you may come across in ephemerides translates to in celestia (not all are always used)

Epoch: Epoch (obviously enough)
e : eccentricity
incl : inclination
node : ascending node
Peri : arg of pericenter
q : periapsis distance (hardly ever used in celestia)
M or MA : mean anomaly
A : semi major axis
PR or per : (orbital) period

Theres no orbital period or semi major axis in the NEAT comet ephemeris so you cant really put it into celestia directly... you could probably work out these 2 values but i dont know how..
You might be able to find an estimate for these values somewhere else on the net- maybe the site of the people who discovered it...?

Maybe someone else knows where to get these values?!

[selden]

Unfortunately, there is not just one NEAT comet, there are many: NEAT is the Near Earth Asteroid Tracking program.

However, a search of the Horizons database found the one you're looking for. Horizons provides the orbital elements that Celestia needs for elliptical oribits. Unfortunately, many comets are actually in parabolic or hyperbolic orbits, which Celestia can't handle just yet. Its EllipticalOrbit definition requires a period, and such a thing doesn't exit for orbits with an eccentricity of 1 or more. Fortunately that's not the case for C/2002 V1, although it's *extremely* close.

Below are the heliocentric Keplerian orbital elements calculated by Horizons. Most of the orbital parameters can be used directly by Celestia. The period has to be converted into years, though. Or you can recalculate the period from the semi-major axis: period = sma **1.5

I hope this helps.

Code: Select all

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JPL/HORIZONS                  NEAT (C/2002 V1)             2003-Mar-14 14:18:17
Rec #:400412 (COV)    Soln.date: 2003-Feb-15_11:50:00     # obs: 1439 (95 days)



2452711.500000000 = A.D. 2003-Mar-13 00:00:00.0000 (CT)
 EC= 9.999130594524440E-01 QR= 9.926579430550385E-02 IN= 8.171594624410443E+01
 OM= 6.408793320853832E+01 W = 1.521677433628649E+02 Tp= 2.452688796044608E+06
 N = 2.554689937525480E-05 MA= 5.800156638534622E-04 TA= 1.386146918438570E+02
 A = 1.141766380550904E+03 AD= 2.283433495307502E+03 PR= 1.409172967380545E+07

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Coordinate system description:

  Ecliptic and Mean Equinox of Reference Epoch

    Reference epoch: J2000.0
    xy-plane: plane of the Earth's orbit at the reference epoch
    x-axis  : out along ascending node of instantaneous plane of the Earth's
              orbit and the Earth's mean equator at the reference epoch
    z-axis  : perpendicular to the xy-plane in the directional (+ or -) sense
              of Earth's north pole at the reference epoch.

Symbol meaning [1 AU=149597870.691 km, 1 day=86400.0 s]:

    JDCT     Epoch Julian Date, Coordinate Time
      EC     Eccentricity, e
      QR     Periapsis distance, q (AU)
      IN     Inclination w.r.t xy-plane, i (degrees)
      OM     Longitude of Ascending Node, OMEGA, (degrees)
      W      Argument of Perifocus, w (degrees)
      Tp     Time of periapsis (Julian day number)
      N      Mean motion, n (degrees/day)
      MA     Mean anomaly, M (degrees)
      TA     True anomaly, nu (degrees)
      A      Semi-major axis, a (AU)
      AD     Apoapsis distance (AU)
      PR     Orbital period (day)
 Computations by ...
     Solar System Dynamics Group, Horizons On-Line Ephemeris System
     4800 Oak Grove Drive, Jet Propulsion Laboratory
     Pasadena, CA  91109   USA
     Information: http://ssd.jpl.nasa.gov/
     Connect    : telnet://ssd.jpl.nasa.gov:6775  (via browser)
                  telnet ssd.jpl.nasa.gov 6775    (via command-line)
     Author     : Jon.Giorgini@jpl.nasa.gov
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