Sources
The principal source for Alcyone Ephemeris is Steve Moshier's analytical ephemeris based upon trigonometric expansions for the earth and planets and the lunar ephemeris ELP2000-85 of Chapront-Touzé and Chapront for the moon, both adjusted to Jet Propulsion Laboratory's DE404. Moshier's ephemeris is described and the files can be downloaded at www.moshier.net (see aa-56.zip and further details on aa-56.zip, which contains references to Moshier's sources, as does the Readme file in aa-56.zip). Alcyone Ephemeris is further adjusted to JPL's DE406 by a series of corrections, some optional, described below in Accuracy. Algorithms for reduction to geocentric coordinates, precession, and nutation are from Moshier, and additional algorithms are applied to compute velocities, accelerations, and transformations of coordinates, including topocentric coordinates with corrections for parallax and refraction. The ephemeris is quite fast; with an 1600mgh Athlon processor, 100 calculations of geocentric longitude, latitude, and distance for the sun, moon, and all planets take about 2 seconds, 100 calculations of differences for all of these about 4 seconds. Alcyone Ephemeris is also very compact, about 20 mgb, compared to nearly 200 mgb of data files for DE406. The following ephemeris types are independent of Moshier's ephemeris:
Apparent magnitudes of planets are
computed in three ways: from formulas and coefficients of G. Müller, used
in the Astronomical Almanac until 1984, from coefficients in the
Astronomical Almanac since 1984, and from coefficients in tables
7.41.1 to 7.47.1 of the Explanatory Supplement to the Astronomical
Almanac (1992).
Lunar libration, position angle of the
lunar axis, and selenographic coordinates of the sun and position angle of
the limb are from Jean Meeus, Astronomical Algorithms,
2nd ed., Wilmann-Bell, 1998.
Mean orbital elements are from Meeus,
Astronomical Algorithms; these are not identical to the elements
used for the ephemeris calculations although the differences, except
perhaps at early epochs, are very small.
Osculating lunar orbital elements are
from Michelle Chapront-Touzé and Jean Chapront, Lunar Tables and
Programs from 4000 B.C. to A.D. 8000, Willmann-Bell, 1991.
Delta T. The formulas for computation of delta T and the table from the Astronomical Almanac used for interpolation, along with a discussion of methods of determining delta T, can be found at http://www.phys.uu.nl/~vgent/astro/deltatime.htm. Definitions of systems of astronomical time, including ET, UT, and more recent systems, can be found at http://www.gb.nrao.edu/~rfisher/Ephemerides/times.html.
Alcyone Ephemeris
Documentation
(C) 2007 Alcyone
Software