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
(SAOJ2000)
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.
