astro(7) [plan9 man page]
ASTRO(7) Miscellaneous Information Manual ASTRO(7) NAME
astro - print astronomical information SYNOPSIS
astro [ -dlepsatokm ] [ -cn ] DESCRIPTION
Astro reports upcoming celestial events, by default for 24 hours starting now. The options are: d Read the starting date. A prompt gives the input format. l Read the north latitude, west longitude, and elevation of the observation point. A prompt gives the input format. If l is missing, the initial position is read from the file /lib/sky/here. c Report for n (default 1) successive days. e Report fractional overlap during eclipses. p Print the positions of objects at the given time rather than searching for interesting conjunctions. For each, the name is followed by the right ascension (hours, minutes, seconds), declination (degrees, minutes, seconds), azimuth (degrees), elevation (degrees), and semidiameter (arc minutes). For the sun and moon, the magnitude is also printed. s Print output in English words suitable for speech synthesizers. a Include a list of artificial earth satellites for interesting events. (There are no orbital elements for the satellites, so this option is not usable.) t Read /T from standard input. /T is the difference between ephemeris and universal time (seconds) due to the slowing of the earth's rotation. /T is normally calculated from an empirical formula. This option is needed only for very accurate timing of occultations, eclipses, etc. o Search for stellar occultations. k Print times in local time (`kitchen clock') as described in the timezone environment variable. m Includes a single comet in the list of objects. This is modified (in the source) to refer to an approaching comet but in steady state usually refers to the last interesting comet (currently Levy, 1990c). FILES
/lib/sky/estartab ecliptic star data /lib/sky/here default latitude (N), longitude (W), and elevation (meters) SOURCE
/sys/src/cmd/astro SEE ALSO
scat(7) BUGS
The k option reverts to GMT outside of 1970-2036. ASTRO(7)
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GENSKY(1) General Commands Manual GENSKY(1) NAME
gensky - generate a RADIANCE description of the sky SYNOPSIS
gensky month day time [ options ] gensky -ang altitude azimuth [ options ] gensky -defaults DESCRIPTION
Gensky produces a RADIANCE scene description for the CIE standard sky distribution at the given month, day and time. By default, the time is interpreted as local standard time on a 24-hour clock. The time value may be given either as decimal hours, or using a colon to sepa- rate hours and minutes. If the time is immediately followed (no white space) by a North American or European time zone designation, then this determines the standard meridian, which may be specified alternatively with the -m option. The following time zones are understood, with their corresponding hour differences from Greenwich Mean Time: Standard time: YST PST MST CST EST GMT 9 8 7 6 5 0 CET EET AST GST IST JST NZST -1 -2 -3 -4 -5.5 -9 -12 Daylight savings time: YDT PDT MDT CDT EDT BST 8 7 6 5 4 -1 CEST EEST ADT GDT IDT JDT NZDT -2 -3 -4 -5 -6.5 -10 -13 If the time is preceded by a plus sign ('+'), then it is interpreted as local solar time instead. It is very important to specify the cor- rect latitude and longitude (unless local solar time is given) using the -a and -o options to get the correct solar angles. The second form gives the solar angles explicitly. The altitude is measured in degrees above the horizon, and the azimuth is measured in degrees west of South. The third form prints the default option values. The output sky distribution is given as a brightness function, skyfunc. Its value is in watts/steradian/meter2. The x axis points east, the y axis points north, and the z axis corresponds to the zenith. The actual material and surface(s) used for the sky is left up to the user. For a hemispherical blue sky, the description might be: !gensky 4 1 14 skyfunc glow skyglow 0 0 4 .99 .99 1.1 0 skyglow source sky 0 0 4 0 0 1 180 Often, skyfunc will actually be used to characterize the light coming in from a window. In addition to the specification of a sky distribution function, gensky suggests an ambient value in a comment at the beginning of the description to use with the -av option of the RADIANCE rendering programs. (See rvu(1) and rpict(1).) This value is the cosine-weighted radiance of the sky in watts/steradian/meter2. Gensky supports the following options. -s Sunny sky without sun. The sky distribution will correspond to a standard CIE clear day. +s Sunny sky with sun. In addition to the sky distribution function, a source description of the sun is generated. -c Cloudy sky. The sky distribution will correspond to a standard CIE overcast day. -i Intermediate sky without sun. The sky will correspond to a standard CIE intermediate day. +i Intermediate sky with sun. In addition to the sky distribution, a (somewhat subdued) sun is generated. -u Uniform cloudy sky. The sky distribution will be completely uniform. -g rfl Average ground reflectance is rfl. This value is used to compute skyfunc when Dz is negative. Ground plane brightness is the same for -s as for +s. (Likewise for -i and +i, but see the -r option below.) -b brt The zenith brightness is brt. Zenith radiance (in watts/steradian/meter2) is normally computed from the sun angle and sky tur- bidity (for sunny sky). It can be given directly instead, using this option. -B irrad Same as -b, except zenith brightness is computed from the horizontal diffuse irradiance (in watts/meter2). -r rad The solar radiance is rad. Solar radiance (in watts/steradian/meter2) is normally computed from the solar altitude. This option may be used to override the default calculation. If a value of zero is given, no sun description is produced, and the contribu- tion of direct solar to ground brightness is neglected. -R irrad Same as -r, except solar radiance is computed from the horizontal direct irradiance (in watts/meter2). -t trb The turbidity factor is trb. Greater turbidity factors correspond to greater atmospheric scattering. A turbidity factor of 1.0 indicates an ideal clear atmosphere (i.e. a completely dark sky). Values less than 1.0 are physically impossible. The following options do not apply when the solar altitude and azimuth are given explicitly. -a lat The site latitude is lat degrees north. (Use negative angle for south latitude.) This is used in the calculation of sun angle. -o lon The site longitude is lon degrees west. (Use negative angle for east longitude.) This is used in the calculation of solar time and sun angle. Be sure to give the corresponding standard meridian also! If solar time is given directly, then this option has no effect. -m mer The site standard meridian is mer degrees west of Greenwich. (Use negative angle for east.) This is used in the calculation of solar time. Be sure to give the correct longitude also! If a time zone or solar time is given directly, then this option has no effect. EXAMPLE
To produce a sunny sky for July 4th at 2:30pm Eastern daylight time at a site latitude of 42 degrees, 89 degrees west longitude: gensky 7 4 14:30EDT +s -a 42 -o 89 To produce a sunny sky distribution for a specific sun position but without the sun description: gensky -ang 23 -40 -s FILES
/usr/share/radiance/skybright.cal AUTHOR
Greg Ward SEE ALSO
rpict(1), rvu(1), xform(1) RADIANCE
4/24/98 GENSKY(1)