1. INTRODUCTION
1.1. Why do we need precise planetary positions?
There are several good reasons why we need precise planetary positions.
I will mention just a few that impact the U.S. Naval Observatory and its
various scientific (and military) programs and objectives. There are two
broad requirement categories: Department of Defense (DoD) requirements
and astronomical requirements, which overlap significantly. First, for ord-
nance guiding and targeting purposes, the DoD requires stellar positions to
MODELING PLANETARY MOTIONS:
WHY WE CARE AND HOW WE DO IT
M
ARC
A. M
URISON
Astronomical Applications Dept., U.S. Naval Observatory, 3450 Massachusetts Ave,
NW
,
Washington DC 20392 USA
murison@aa.usno.navy.mil
March 5, 1999
ABSTRACT
Presented is a review of high-precision modeling of the mo-
tions of solar system objects, especially the planets. Motiva-
tions are discussed, as are various astronomical reference
frames and their interdependence. We then discuss, in broad
terms, how one generates a high-precision ephemeris and the
kinds of observations that such an ephemeris depends upon.
Following that, we review Newcomb, a new high-precision
ephemeris program currently under development at the U.S.
Naval Observatory. This new program takes full advantage of
modern programing design and techniques, including object
orientation and graphical user interfaces. We close with a
brief description of the three main modules of Newcomb and
how they work.
Key words: solar system -- ephemerides -- celestial mechan-
ics
