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     SCAT(7)                                                   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
               (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 Cat-
               alogue.  Output identifies the visual and photographic
               magnitudes, 2000.0 coordinates, proper motion, spectral
               type, multiplicity and variability class, and HD num-
               ber.

          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

     SCAT(7)                                                   SCAT(7)

               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 out-
               put 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 speci-
                 fied 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 informa-
                 tion available for the objects in the set.
          print  Print the contents of the set.  If the information

     SCAT(7)                                                   SCAT(7)

                 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 500×500 pixel block from the survey con-
                 taining 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 dis-
                 plays with ldepth 3.  Scat does not change the hard-
                 ware 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'

     SCAT(7)                                                   SCAT(7)

     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
          by permission.  The Digitized Sky Survey, 102 CD-ROMs, is
          not distributed with the system.