C2A gives you access to the Hipparcos catalogue. This catalogue gives the positions, proper motions, the BT and VT magnitudes and several other pieces of information for 118,218 stars for the whole celestial sphere. The Hipparcos catalogue is produced by the mission of the same name launched by the European Space Agency. The satellite, which operated for 4 years, produced high quality scientific data from November 1989 to March 1993. You select the Hipparcos catalogue as the current catalogue through the Stars tab of the Options dialogue box, or by SHIFT-right-clicking on the map.
C2A takes into account the proper motions given in the Hipparcos catalogue in determining star positions at a date specified by the user.
If you have the original Hipparcos catalogue, the Tools page of the C2A Website provides a tool for compiling it in the C2A format. All the information needed to compile the catalogue is given on that page. Note that the Hipparcos catalogue compiled for C2A is now systematically integrated into the distribution of the C2A software.