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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
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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.
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ic1234
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Like NGC references, but from the Index Catalog.
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sao12345
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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.
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m4 Catalog number 4 in Messier's catalog. The output is the NGC
number.
abell1701
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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.
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planetarynebula
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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.
"
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α umi"
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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.
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12h34m –16
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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.
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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
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astro. The positions are current at the start of scat 's execution;
see the astro command in the next section for more information.
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The commands are:
add itemAdd the named item to the set.
keep class ...
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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.
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drop class ...
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
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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.
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astro option
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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.
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plot option
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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.
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plate [[ra dec] rasize [decsize]]
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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.
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gamma value
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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
colors(1)) on an 8–bit color–mapped display.
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