GSC-ACT files and information  Last updated 9 April 2003    •
Overview of the project   • Accessing GSC-ACT data via Internet
• Getting GSC-ACT on two CD-ROMs (cheap)   • Methods used   •
Summary of results   • How much of an improvement is GSC-ACT
over GSC 1.x?   • What about photometry?   • How to use this
data   • Overview of the project:      Please note that, for
almost all uses, GSC-ACT is now obsolete. Catalogues such as
GSC-2.2, UCAC-3, B1.0, and A2.0 all offer more stars and better
positions and magnitudes than GSC-ACT. (In particular, the
release of UCAC-3 in August 2009 rendered GSC-ACT completely
obsolete.) Much of what follows, therefore, is of historical
interest only. The area of star catalogues is a very rapidly
changing one.      The purpose of the GSC-ACT project is to
recalibrate the Hubble Guide Star Catalog (GSC), version 1.1,
using the ACT (Astrographic Catalog/Tycho) data from the US
Naval Observatory.      The reasons for doing this will be
apparent to long-time GSC 1.1 users. GSC 1.