SKY(VI) 9/22/73 SKY(VI)
NAME
sky - obtain ephemerides
SYNOPSIS
sky
DESCRIPTION
Sky predicts the apparent locations of the Sun, the Moon,
the planets out to Saturn, stars of magnitude at least 2.5,
and certain other celestial objects Sky reads the standard
input to obtain a GMT time typed on one line with blanks
separating year, month number, day, hour, and minute; if the
year is missing the current year is used. If a blank line
is typed the current time is used. The program prints the
azimuth, elevation, and magnitude of objects which are above
the horizon at the ephemeris location of Murray Hill at the
indicated time.
Placing a ``1'' input after the minute entry causes the
program to print out the Greenwich Sidereal Time at the
indicated moment and to print for each body its right
ascension and declination as well as its azimuth and
elevation. Also, instead of the magnitude, the geocentric
distance of the body, in units the program considers
convenient, is printed. (For planets the unit is
essentially A. U.)
The magnitudes of Solar System bodies are not calculated and
are given as 0. The effects of atmospheric extinction are
not included; the mean magnitudes of variable stars are
marked with ``*''.
For all bodies, the program takes into account precession
and nutation of the equinox, annual (but not diurnal)
aberration, diurnal parallax, and the proper motion of stars
(but not annual parallax). In no case is refraction
included.
The program takes into account perturbations of the Earth
due to the Moon, Venus, Mars, and Jupiter. The expected
accuracies are: for the Sun and other stellar bodies a few
tenths of seconds of arc; for the Moon (on which particular
care is lavished) likewise a few tenths of seconds. For the
Sun, Moon and stars the accuracy is sufficient to predict
the circumstances of eclipses and occultations to within a
few seconds of time. The planets may be off by several
minutes of arc.
FILES
/usr/lib/startab, /usr/lib/moontab
SEE ALSO
azel (VI)
American Ephemeris and Nautical Almanac, for the appropriate
years; also, the Explanatory Supplement to the American
Ephemeris and Nautical Almanac.
AUTHOR
R. Morris
BUGS