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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  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 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)=unveri‐
	      fied  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, galac‐
	      tic 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 coor‐
	      dinates 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.

       mars   The 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 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 flat‐
	      tens 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, execut‐
	      ing 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 unla‐
	      beled 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
	      512×512; 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 dis‐
	      played 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 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  constel‐
       lation names.

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

								       SCAT(7)
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