An ephemeris provides a means for quickly estimating the positions, and sometimes orientations, of solar system bodies as a function of time.

An ephemeris provides a means for quickly estimating the positions, and sometimes orientations, of solar system bodies as a function of time.

Ephemerides used to be in the form of printed lists of positions of heavenly bodies tabulated at fixed intervals of time. High accuracy ephemerides are now more likely to be in the form of tables of Chebyshev polynomial coefficients stored in a binary data file. Software is needed to find the right set of coefficients based on the time interval and body of interest, and then to apply those to obtain the position and orientation of the body at the specific point of time. Additional software may be needed to transform those data into the desired form (e.g., relative position, right ascension and declination, azimuth and elevation).

The producers of the highest precision ephemerides include the Jet Propulsion Laboratory, which produces the JPL Development Ephemeris and Small Body Ephemerides series of ephemeris models; the Institute of Applied Astronomy at the Russian Academy of Sciences, who produce the Ephemerides of the Planets and Moon (EPM) series of ephemerides; and the IMCCE at the Observatory of Paris, which produces the INPOP series of ephemerides.

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