Ephem is a program that displays ephemerides for all the planets plus any
two additional objects. The additional objects may be fixed or specified
via heliocentric elliptical, hyperbolic or parabolic orbital elements to
accommodate solar system objects such as asteroids or comets.
Information displayed about each object includes RA and Dec precessed to
any epoch, local azimuth and altitude, heliocentric coordinates, distance
from sun and earth, solar elongation, angular size, visual magnitude,
illumination percentage, local rise, transit and set times, length of time
up, constellation, and angular separations between all combinations of
objects. A special detail of Jupiter's moons and central meridian
longitude is also available.
Observing circumstance information includes UTC and local date and time,
local sidereal time, times of astronomical twilight, length of day and
night, local temperature, pressure and height above sea level for the
refraction model and a monthly calendar.
RA/Dec calculations are geocentric and include the effects of light travel
time, nutation, aberration and precession. Alt/az and rise/set/transit
and, optionally, angular separation calculations are topocentric and
include the additional effects of parallax and refraction.
Plot and listing files of selected field values may be generated as the
program runs. The plot files are full precision floating point values in
ASCII intended for export to other plotting programs. The listing files
are tables formatted for more general human reading. Ephem includes
simple quick-look facilities to view these files.
One may watch the sky or the solar system with a simple character-oriented
screen display.
Ephem may be asked to search for interesting conditions automatically,
using several algorithms. Most fields displayed on the screen may be used
as terms in an arbitrary arithmetic expression that can be solved for
local zero or extrema, or the time of state change of any boolean
expression can be found.
The program is some 11,000 lines of C. It uses only a very simple set of
io routines and should be easily ported to any 24x80 ASCII display. To
date, it has been ported to several flavors of Unix, VMS, MS-DOS and,
simplistically, the Macintosh using Think-C.
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