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- .TH SKY 6
- .SH NAME
- sky \- obtain ephemerides
- .SH SYNOPSIS
- .B /usr/games/sky
- [
- .B \-l
- ]
- .SH DESCRIPTION
- .I 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.
- .I Sky\^
- reads the standard input to obtain
- a \s-1GMT\s0 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 \f3\-\^l\fP flag causes it to ask for another location.
- .PP
- 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.
- .PP
- A ``2'' after the minute entry makes the coordinate system geocentric.
- .PP
- The effects of atmospheric extinction
- on magnitudes
- are not included;
- the brightest magnitudes
- of variable stars are marked with \(**.
- .PP
- 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.
- .PP
- 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.
- .PP
- 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.
- .PP
- For the most accurate use of the program it is necessary
- to know that it actually runs in Ephemeris time.
- .SH FILES
- /usr/lib/startab
- .SH "AUTHOR"
- Robert H. Morris, AT&T Bell Labs.
- .SH "SEE ALSO"
- .ft I
- .IR "American Ephemeris and Nautical Almanac" ,
- for the appropriate years;
- also, the
- .IR "Explanatory Supplement to the American Ephemeris and Nautical Almanac" .
-