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|JEphem Ephemeris trail Pluto 99|
Pluto99 Characteristics Building and testing positions Obtaining the velocities Testing velocities Remarks
I couldn't find the official name of the theory I used to compute Pluto ephemeris, so I called it "Pluto99", as it has been released in 1999.
The theory is from Jean Chapront and Gérard Francou from the "Observatoire de Paris" (Paris Observatory).
The original files can be found at ftp://ftp.bdl.fr/pub/polac/solarsys/pluto. Files plutoxyz.dat, plutoxyz.for and notice have been used.
The resulting class to compute Pluto coordinates is
Tables of Pluto's motion have been constructed by the first author using a method of approximation based on frequency analysis as described in the paper : Representation of planetary ephemerides by frequency analysis. Application to the five outer planets. Astron. & Astrophys.Suppl. Ser., 109, 191 (1995). This representation uses the results of the numerical integration DE406 of the Jet Propulsion Laboratory as a source. The interval of validity covers 2185000 days (60 centuries approximately). Start : Apr 23 -2998 0h, Julian date 626150.5 End : Jul 26 2984 0h, Julian date 2811150.5 The reference frame is defined with dynamical equinox and ecliptic J2000. The time scale is Barycentric Dynamical Time (TDB). The largest discrepancy obtained by a comparison with the source DE406 is 0.00005 ua.Precision of the theory in arc seconds :
BuilTestPluto99(see its javadoc or code source).
BuildTestPluto99.buildPluto99(). In notice, thet say that "The largest discrepancy obtained by a comparison with the source DE406 is 0.00005 ua" ; seen from Earth, this corresponds to a maximal error of 0.37 arc second (for a geocentric opposition Sun - Pluto, when distance from Pluto to Sun was minimal - see
BuilTestPluto99.calcGeoPrec()). I thought it was no use to build a light version giving a precision of one arc second.
Pluto99.java: I included the previously built arrays in
Pluto99.javawith cut'n'paste. I then wrote the method to perform the computation (
Pluto99.calcCoord()), from the informations found in notice. As it's straightforward, I don't detail this here.
BuildTestPluto99.testPositions(). The differences between reference values from the BDL and JEphem values are about 10-7 u.a., which is OK, as the announced precision is 10-5 u.a.
buildPluto99(), I generated an other class with values in radians.
|We have :||x = a*t + b|
BuildTestPluto99.testVelocities()). To test the velocity at instant t, it computes the position at t - dt and t + dt, computes the average velocity and compares it to the value obtained with the preceding formula at instant t.
Pluto99.calcCoord()is NOT used ; all the terms are taken for the summation.