From the information page of the US Naval Observatory:
http://www.usno.navy.mil/USNO/astrom...l-IR-prod/ucac
" UCAC is an astrometric, observational program, which started in
" February 1998 at CTIO. All sky observations were completed at the
" Naval Observatory's Flagstaff Station in May 2004, and data
" reduction was completed in July 2009. The UCAC3 catalog was
" released on August 10, 2009 at the IAU General Assembly in Rio de
" Janero, Brazil. Bug fixes, reduction improvements, use of NPM
" data for proper motions and inclusion of APASS 5-band photometry
" lead to the final UCAC4.
"
" UCAC4: By mid 2011 a first version of the UCAC4 was produced. It
" was sent to a number of testers worldwide. Feedback comments were
" received and by the end of 2012 an improved version of UCAC4 was
" produced which has further been investigated. Now we have an
" almost final version for about 113 million stars.
"
" UCAC4 does not use any Schmidt plate data. Proper motions of
" faint stars north of Dec = -20 deg are now based on NPM
" data. Besides 2MASS near-IR photometry (as in previous releases)
" UCAC4 now includes APASS 5-band photometry. The APASS data
" release #6 is expected to become available in May 2012 to
" complete the all-sky coverage. It has been decided to wait with
" the UCAC4 release to include APASS DR6 data. Thus the public
" release of UCAC4 is scheduled for June 2012.
"
" The UCAC4 data will be sent to CDS Strasbourg at that time and a
" double-sided DVD with the UCAC4 release files will be sent to
" addresses on our distribution list (UCAC2, UCAC3 customers). In
" order to assist users and 3rd party software vendors to interface
" with UCAC4, the following files are now available:
" [...]
Information how to request the free 2-sided DVD is at the above URL.
I know of two programs that can function with this disk, XEphem and
CdC, and there may be others.
XEphem, the premier UNIX/Linux (and Windows/Cygwin) research program:
http://www.clearskyinstitute.com/xephem/
http://tech.groups.yahoo.com/group/xephem/
CdC (Cartes du Ciel aka SkyChart) for Linux and Windows:
http://www.ap-i.net/skychart/start
http://www.ap-i.net/skychart/en/news/ucac4_catalog
Thad