NAME
scat – sky catalogue and Digitized Sky Survey

SYNOPSIS
scat

DESCRIPTION
Scat looks up items in catalogues of objects outside the solar system and implements database–like manipulations on sets of such objects. It also provides an interface to astro(7) to plot the locations of solar system objects. Finally, it displays images from the Space Telescope Science Institute's Digitized Sky Survey, keyed to the catalogues.

Items are read, one per line, from the standard input and looked up in the catalogs. Input is case–insensitive. The result of the lookup becomes the set of objects available to the database commands. After each lookup or command, if more than two objects are in the set, scat prints how many objects are in the set; otherwise it prints the objects' descriptions or cross–index listings (suitable for input to scat). An item is in one of the following formats:
ngc1234
Number 1234 in the New General Catalogue of Nonstellar Objects, NGC2000.0. The output identifies the type (Gx=galaxy, Pl=planetary nebula, OC=open cluster, Gb=globular cluster, Nb=bright nebula, C+N=cluster associated with nebulosity, Ast=asterism, Kt=knot or nebulous region in a galaxy, ***=triple star, D*=double star, ?=uncertain, –=nonexistent, PD=plate defect, and (blank)=unverified or unknown), its position in 2000.0 coordinates, its size in minutes of arc, a brief description, and popular names.
ic1234
Like NGC references, but from the Index Catalog.
sao12345
Number 12345 in the Smithsonian Astrophysical Star Catalogue. Output identifies the visual and photographic magnitudes, 2000.0 coordinates, proper motion, spectral type, multiplicity and variability class, and HD number.
m4    Catalog number 4 in Messier's catalog. The output is the NGC number.
abell1701
Catalog number 1701 in the Abell and Zwicky catalog of clusters of galaxies. Output identifies the magnitude of the tenth brightest member of the cluster, radius of the cluster in degrees, its distance in megaparsecs, 2000.0 coordinates, galactic latitude and longitude, magnitude range of the cluster (the `distance group'), number of members (the `richness group'), population per square degree, and popular names.
planetarynebula
The set of NGC objects of the specified type. The type may be a compact NGC code or a full name, as above, with no blank.
"
α umi"
Names are provided in double quotes. Known names are the Greek letter designations, proper names such as Betelgeuse, bright variable stars, and some proper names of stars, NGC objects, and Abell clusters. Greek letters may be spelled out, e.g. alpha. Constellation names must be the three–letter abbreviations. The output is the SAO number. For non–Greek names, catalog numbers and names are listed for all objects with names for which the given name is a prefix.
12h34m –16
Coordinates in the sky are translated to the nearest `patch', approximately one square degree of sky. The output is the coordinates identifying the patch, the constellations touching the patch, and the Abell, NGC, and SAO objects in the patch. The program prints sky positions in several formats corresponding to different precisions; any output format is understood as input.
umi   All the patches in the named constellation.
marsThe planets are identified by their names. The names shadow and comet refer to the earth's penumbra at lunar distance and the comet installed in the current astro(7). The output is the planet's name, right ascension and declination, azimuth and altitude, and phase for the moon and sun, as shown by
astro. The positions are current at the start of scat 's execution; see the astro command in the next section for more information.

The commands are:
add itemAdd the named item to the set.
keep class ...
Flatten the set and cull it, keeping only the specified classes. The classes may be specific NGC types, all stars (sao), all NGC objects (ngc), all M objects (m), all Abell clusters (abell), or a specified brightness range. Brightness ranges are specified by a leading > or < followed by a magnitude. Remember that brighter objects have lesser magnitudes.
drop class ...
Complement to keep.
flat    Some items such as patches represents sets of items. Flat flattens the set so scat holds all the information available for the objects in the set.
print   Print the contents of the set. If the information seems meager, try flattening the set.
expand n
Flatten the set, expand the area of the sky covered by the set to be n degrees wider, and collect all the objects in that area. If n is zero, expand collects all objects in the patches that cover the current set.
astro option
Run astro(7) with the specified options (to which will be appended –p), to discover the positions of the planets. Astro's –d and –l options can be used to set the time and place; by default, it's right now at the coordinates in /lib/sky/here. Running astro does not change the positions of planets already in the display set, so astro may be run multiple times, executing e.g. add mars each time, to plot a series of planetary positions.
plot option
Expand and plot the set in a new window on the screen. Symbols for NGC objects are as in Sky Atlas 2000.0, except that open clusters are shown as stippled disks rather than circles. Abell clusters are plotted as a triangle of ellipses. The planets are drawn as disks of representative color with the first letter of the name in the disk (lower case for inferior planets; upper case for superior); the sun, moon, and earth's shadow are unlabeled disks. Objects larger than a few pixels are plotted to scale; however, scat does not have the information necessary to show the correct orientation for galaxies. The option nogrid suppresses the lines of declination and right ascension. By default, scat labels NGC objects, Abell clusters, and bright stars; option nolabel suppresses these while alllabel labels stars with their SAO number as well. The default size is 512x512; options dx n and dy n set the x and y extent. The option zenithup orients the map so it appears as it would in the sky at the time and location used by the astro command (q.v.).
The output is designed to look best on an LCD display. CRTs have trouble with the thin, grey lines and dim stars. The option nogrey uses white instead of grey for these details, improving visibility at the cost of legibility when plotting on CRTs.
plate [[ra dec] rasize [decsize]]
Display the section of the Digitized Sky Survey (plate scale approximately 1.7 arcseconds per pixel) centered on the given right ascension and declination or, if no position is specified, the current set of objects. The maximum area that will be displayed is one degree on a side. The horizontal and vertical sizes may be specified in the usual notation for angles. If the second size is omitted, a square region is displayed. If no size is specified, the size is sufficient to display the centers of all the objects in the current set. If a single object is in the set, the 500x500 pixel block from the survey containing the center of the object is displayed. The survey is stored in the CD–ROM juke box; run 9fs juke before running scat.
gamma value
Set the gamma for converting plates to images. Default is –1.0. Negative values display white stars, positive black. The images look best on displays with depth 8 or greater. Scat does not change the hardware color map, which should be set externally to a grey scale; try the command getmap gamma (see getmap(9.1)) on an 8–bit color–mapped display.

EXAMPLES
Plot the Messier objects and naked–eye stars in Orion.
ori
keep m <6
plot nogrid

Draw a finder chart for Uranus:
uranus
expand 5
plot

Show a partial lunar eclipse:
astro –d
2000 07 16 12 45
moon
add shadow
expand 2
plot

Draw a map of the Pleiades.
"
alcyone"
expand 1
plot

Show a pretty galaxy.
ngc1300
plate 10'

FILES
/lib/sky/*.scat

SOURCE
/sys/src/cmd/scat

SEE ALSO
astro(7)
/lib/sky/constelnames the three–letter abbreviations of the constellation names.

The data was provided by the Astronomical Data Center at the NASA Goddard Space Flight Center, except for NGC2000.0, which is Copyright © 1988, Sky Publishing Corporation, used (but not distributed) by permission. The Digitized Sky Survey, 102 CD–ROMs, is not distributed with the system.

Copyright © 2017 Alcatel-Lucent. All rights reserved.