Unix |
Unix v6 |
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sky(6) |
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sky obtain ephemerides [ ] 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. 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. The
‘−l’ flag causes it to ask for another
location. 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 topographic right ascension and
declination as well as its azimuth and elevation. Also,
instead of the magnitude, the semidiameter of the body, in
seconds of arc, is reported. A ‘‘2’’
after the minute entry makes the coordinate system
geocentric. The effects of atmospheric extinction on
magnitudes are not included; the brightest 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. 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. There are lots of
special options not described here, which do things like
substituting named star catalogs, smoothing nutation and
aberration to aid generation of mean places of stars, and
making conventional adjustments to the Moon to improve
eclipse predictions. For the most accurate use of the
program it is necessary to know that it actually runs in
Ephemeris time. /usr/lib/startab, /usr/lib/moontab azel (VI)
American Ephemeris and Nautical Almanac, for the
appropriate years; also, the Explanatory Supplement to
the American Ephemeris and Nautical Almanac. R.
Morris
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sky(6) |
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