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Astron. Astrophys. 336, 381-384 (1998)

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Time scales in the JPL and CfA ephemerides

E.M. Standish

Caltech / Jet Propulsion Laboratory JPL 301-150; Pasadena, CA 91109, USA (ems@smyles.jpl.nasa.gov)

Received 24 March 1998 / Accepted 12 May 1998


Over the past decades, the IAU has repeatedly attempted to correct its definition of the basic fundamental argument used in the ephemerides. Finally, they have defined a time system which is physically possible, according to the accepted standard theory of gravitation: TCB ("Barycentric Coordinate Time"). Ironically, this time scale is mathematically and physically equivalent to [FORMULA], the time scale that has been used by JPL and by MIT (the group later went to CfA) in their ephemeris creation processes since the 1960's. TCB differs from [FORMULA] by only a constant offset and a constant rate. As such, TCB provides an equivalent alternative to [FORMULA], but it does not allow increased accuracy as others have implied.

Key words: time – ephemerides

Send offprint requests to: E.M. Standish

© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998