The USNO-B Catalog is the most recent catalog produced from the USNO Precision Measuring Machine project. The catalog is over 80 GBytes in size, and thus is too large to be distributed whole over the network to users. Users may obtain data from this catalog, as well as sky charts, using the tools provided through the Interactive Catalog and Image Search. Users with a well justified need for the entire catalog can contact the USNO to request a complete copy of the catalog. Typically this is distributed by exchange of hard disk drives.
A more detailed description of the construction and contents of the USNO-B1 catalog can be found in Monet et al. (2003, "The USNO-B Catalog", AJ, 125, 984).
The Precision Measuring Machine (PMM) in its clean room at the USNO Flagstaff Station. Built by Anorad, Inc. of New York, the base of this machine is a single block of granite weighing roughly 10 tons. It rests on a concrete pier which is isolated from the floor of the room to prevent vibration of the measuring machine. Twin CCD (charge coupled device) cameras are set up to "fly'' a constant distance above the photographic plates, stopping every few seconds to take digital "snapshots'' of a small area of the photographs. The plates rest on a horizontal "plate stage'' supported by four air bearings which float on a thin cushion of air above the granite base.