I have Earth Moon Barycenter coordinate (J2000) generated from VSOP2013 in Astronomical Units,

X=-0.1968857640    Y=0.9633224602     Z=0.0002147057    AU 
X'=-0.0171376156   Y'=-0.0035078892   Z'=-0.0000011481  AU/day

How to convert it to Geocentric?

  • $\begingroup$ Find the coordinates for the Earth's barycenter and subtract. Note the Earth-Moon barycenter actually lies about 1000 miles below the Earth's surface, since the Earth is about 81 times more massive than the Moon. $\endgroup$ – user21 Jul 27 '17 at 14:32

How to convert it to Geocentric?

You don't. That's the position and velocity of the Earth-Moon barycenter with respect to the center of the Sun. Converting that to geocentric (a) doesn't make sense, and (b) even if it did, can't be done without knowing the location of the Earth-Moon barycenter in geocentric coordinates.

The position of the Earth-Moon barycenter plus the geocentric inertial position of the Moon expressed in the J2000 ecliptic frame plus the Earth-Moon mass ratio lets you compute the position of the Earth with respect to the Sun (or the position of the Sun with respect to the Earth). Add information about the positions of other planets with respect to the Sun and you can compute the positions of those other planets with respect to the Earth.

You cannot do the above with VSOP2013 alone because VSOP2013 does not contain information about the position of the Moon with respect to the Earth. You'll need a separate lunar ephemeris for that.

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  • $\begingroup$ what about ELP/MPP02? $\endgroup$ – Muhamad NW Jul 28 '17 at 8:42
  • $\begingroup$ You can try the VSOP2000 which does include the moon... $\endgroup$ – Huy Pham May 14 '18 at 6:56

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