ACKNOWLEDGEMENTS:


Thanks are due to the National Space Sciences Data Center for the original
versions of the object catalogs which have been abridged for use of the
xsky program.

Thanks also to PC Leyland, who provided a BASIC program called PRECESS.BAS,
from which I extracted the algorithm and constants used in the precession
code.

A big thanks to Jim Sharpe, who was the original beta tester and made sure
xsky worked on HP and SGI machines.  He also provided a number of useful
suggestions for improving the utility of the user interface.

The handling of larger catalogs, such as SAO, was speeded up greatly by
Brian Wing, who wrote a routine to pre-screen objects for inclusion in the
display while avoiding a lot of spherical trigonometry.  Only after an
object passes Brian's quick test does it fall into the normal code, which
does a definitive, but compute-intensive, analysis.  This hack speeds up
the SAO catalog at the default display scale by a factor of fifteen, giving
two-second update times on my DECstation 5000/200.

Bill Owen at JPL and Mike Delevoryas pointed me to Nancy G. Roman's paper
in PASP which described a clever method of determining the constellation
containing a given point on the sky.  Bill Owen was also kind enough to
track down the correct values after I discovered an error in the constel-
lation boundary data as distributed by NASA ADC.

Finally, thanks to Jean Meeus for writing "Astronomical Algorithms", pub-
lished by Wilmann-Bell.  The clear equations he provides replaced a fair
amount of my own grungy spherical trigonometry.

Let me take this opportunity to say something about free software on the net.
I've benefitted greatly over the years from free software, and so has xsky.

A)  EMACS is merely *the* editor (thanks, RMS)

B)  ups is the debugger of choice; writing xsky would have been much harder
	without it (thanks, Mark Russell)

C)  and, of course, xsky would have been impossible without X11 and the
	Athena widgets from MIT (thanks to lots of people)

So xsky is free to pay back the net.community for many years of helping me.
Thanks, folks.

Terry R. Friedrichsen

terry@venus.sunquest.com  (Internet)
uunet!sunquest!terry      (Usenet)
terry@sds.sdsc.edu        (alternate address; I live in Tucson)
