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		   xsky 2.0 - a computerized sky atlas

xsky is an X Window System program which allows the user to view the sky and
create customized star charts.

xsky  makes  use  of  machine-readable  astronomical  object  catalogs  made
available by the National Space Sciences Data Center, located at the Goddard
Spaceflight Center  in Greenbelt, Maryland, which  is  administrated by  the
National  Aeronautics and  Space Administration.  Thanks are due to them for
providing this much-needed data distribution service.

Supported catalogs are (abbreviations used by xsky in parentheses):
    a)  the Yale Catalog of Bright Stars (YBS)
    b)  the Revised New General Catalog of Non-Stellar Objects (RNGC)
    c)  the Revised Optical Catalog of Quasi-Stellar Objects (QSO)

Support is included  for the following catalogs, but the catalogs themselves
are not included in this distribution:
    d)  the Smithsonian Astrophysical Observatory Star Catalog (SAO)
    e)  the General Catalog of Variable Stars (VAR)
    f)  the Washington Catalog of Double Stars (DBL)

Support is included for the following catalogs on the NASA Astronomical Data
Center CD-ROM:
    g)  the Bright Star Catalog, 5th revised edition (BSC5)
    h)  the Smithsonian Astrophysical Observatory Star Catalog, J2000
    i)  the Washington Catalog of Double Stars (WDS)
    j)  the General Catalog of Variable Stars (GCVS)

Please  note  that catalogs (a)  -  (f)  are supported  only in the abridged
versions available as part of the xsky distribution.  Catalogs (a) - (c) are
distributed with xsky, and catalogs (d)  - (f) are available  separately via
anonymous FTP.

Additionally, xsky 2.0 supports a  user catalog; there is  an example in the
file  usercat.example, and  the comments in user.c document the  format more
precisely.   The intention of the  user catalog is to enable the addition of
comets  or  asteriods to  create  customized  finder  charts  for  transient
objects.  To use  it,  create your own catalog in the specified format, name
it usercat.dat, and  place  it  in the  path  pointed to  by the  enviroment
variable USER_PATH.

This  program has been rather thoroughly tested  under Ultrix, running  both
the DEC X11R4 server and the MIT X11R5 server.  It builds from the Imakefile
properly  under  Ultrix  and SunOS.   A Makefile.std  is included  for those
unable or unwilling to fool with imake; it should be necessary only to  edit
the INCLUDES line to use it under SunOS.  xsky has gotten a lot less testing
under SunOS, but all the functionality has been checked out in a preliminary
fashion.  gcc is quite happy to compile a runnable version under SunOS, too;
I haven't tried gcc on a DECstation.

xsky started out as a simple project  to  teach myself how to do programming
in the X Window System, and has  expanded  from there, though  it is not yet
capable of reading mail :-).  As such, the same type of thing may be done in
more than one way in different parts  of the code,  and there may be  better
ways of performing certain tasks.  The techniques  used  depended as much on
what I was trying  to learn at the time  as  on what was  appropriate to the
task.  If you have  any comments along these lines, I would be most happy to
hear them.

Because of  the  original intent of xsky as a learning project, some  of the
stuff  in  the  resources  file is necessary  for proper functioning  of the
program.  Be sure you have the environment  variable XAPPLRESDIR set  to the
path containing the supplied XSky file, or have otherwise arranged for those
resources to be included when you start XSky.

Cartographers may recoil in  disgust  at  the  manner  in  which the  sky is
projected onto the flat screen.  Knowing nothing about cartography, I simply
picked an obvious method, and it seems to work  very  well.  I also  solicit
comments along these lines, but be aware that I am going to request specific
information about what is wrong with a  given method and specific algorithms
for any suggested  changes; I know nothing about the subject myself (but  am
quite willing to learn).

Suggestions for improvements  will also be  noted,  but please be aware that
this is a part-time, off-hours project for me, and implementation could take
awhile.  It would certainly go faster  if you  included  the code along with
your  suggestions!    Any  such  contributions,  if  incorporated,  will  be
gratefully acknowledged.