Astronomical Applications Department, U.S. Naval Observatory novas c 2 doc Page 36
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the JPL ephemerides, which exist as external data files. Additional documentation is
provided on the following pages for the proper use of each version. The user is free to
supply alternative versions, providing that the arguments conform to the above
specifications.
The values of the body identification number,
body
, will in general differ from one
solarsystem
version to another; consult the documentation for the specific version in
use. Usually,
body
= 1 refers to Mercury,
body
= 2 refers to Venus,
body
= 3 refers
to the Earth, etc., but the identification numbers for bodies such as the Sun or Moon vary.
Furthermore, some versions of
solarsystem
support only a subset of the major solar
system bodies. The minimum requirement is support for the Earth. It is also sometimes
necessary to distinguish between the Earth and the Earth/Moon barycenter; for computing
quantities related to observables (e.g., apparent, topocentric, or astrometric places) it is
the position and velocity of the Earth that is required.
