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.TH ASTRO 7
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.SH NAME
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astro \- print astronomical information
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.SH SYNOPSIS
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.B astro
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[
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.B -dlpsatokm
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]
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[
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.B -c
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n
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]
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[
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.B -C
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d
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]
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[
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.B -e
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.I obj1
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.I obj2
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]
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.SH DESCRIPTION
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.I Astro
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reports upcoming celestial events, by default for 24 hours starting now.
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The options are:
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.TP
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.B d
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Read the starting date.
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A prompt gives the input
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format.
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.TP
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.B l
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Read the north latitude, west longitude, and elevation of the observation point.
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A prompt gives the input format.
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If
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.B l
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is missing, the initial position is read from the file
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.BR /lib/sky/here .
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.TP
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.B c
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Report for
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.I n
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(default 1) successive days.
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.TP
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.B C
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Used with
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.BR -c ,
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set the interval to
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.B d
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days (or fractions of days).
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.TP
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.B e
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Report distance between the centers of
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objects, in arc seconds, during eclipses or occultations involving
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.I obj1
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and
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.IR obj2 .
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.TP
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.B p
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Print the positions of objects at the
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given time rather than searching for interesting
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conjunctions.
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For each, the name is followed by
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the right ascension (hours, minutes, seconds),
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declination (degrees, minutes, seconds),
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azimuth (degrees),
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elevation (degrees),
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and semidiameter (arc seconds).
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For the sun and moon, the magnitude is also printed.
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The first line of output presents the date and time,
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sidereal time, and the latitude, longitude, and elevation.
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.TP
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.B s
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Print output in English words suitable for speech synthesizers.
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.TP
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.B a
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Include a list of artificial earth satellites for interesting events.
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(There are no orbital elements for the satellites, so this option
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is not usable.)
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.TP
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.B t
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Read
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ΔT
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from standard input.
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ΔT
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is the difference between ephemeris and
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universal time (seconds) due to the slowing of the earth's rotation.
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ΔT
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is normally calculated from an empirical formula.
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This option is needed only for very accurate timing of
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occultations, eclipses, etc.
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.TP
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.B o
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Search for stellar occultations.
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.TP
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.B k
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Print times in local time (`kitchen clock')
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as described in the
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.B timezone
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environment variable.
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.TP
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.B m
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Includes a single comet in the list of objects.
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This is modified (in the source) to refer to an approaching comet
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but in steady state
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usually refers to the last interesting comet (currently Hale-Bopp, C/1995 O1).
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.SH FILES
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.TF /lib/sky/estartab
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.TP
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.B /lib/sky/estartab
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ecliptic star data
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.TP
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.B /lib/sky/here
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default latitude (N), longitude (W), and elevation (meters)
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.SH SOURCE
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.B /sys/src/cmd/astro
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.SH SEE ALSO
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.IR scat (7)
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.SH BUGS
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The
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.B k
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option reverts to GMT outside of 1970-2036.