SCAT(7) 						 Miscellaneous Information Manual						   SCAT(7)

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 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 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 lon-
	      gitude,  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.

       "a umi"
	      Names are provided in double quotes.  Known names are the Greek letter designations, proper names such as Betelgeuse,  bright  vari-
	      able  stars,  and some proper names of stars, NGC objects, and Abell clusters.  Greek letters may be spelled out, e.g.  alpha.  Con-
	      stellation 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.

       The commands are:

       add item
	      Add 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.

       plot option
	      Expand and plot the set on the screen.  The only option is nogrid to suppress the lines of declination and right ascension.  Symbols
	      for NGC objects are as in Sky Atlas 2000.0.  Abell clusters are plotted as a triangle of ellipses.

       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 bitmaps.	Default is -1.0.  Negative values display white stars, positive black.	The images
	      look best on displays with ldepth 3.  Scat does not change the hardware color map, which should be set externally to a  grey  scale;
	      try the command fb/getmap gamma (see getmap(9.1)).

EXAMPLES

       Plot the NGC objects and naked-eye stars in Orion.
	    ori
	    keep ngc <6
	    plot nogrid

       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 (C)
       1988, Sky Publishing Corporation, used by permission.  The Digitized Sky Survey, 102 CD-ROMs, is not distributed with the system.

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