the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at J2000.0, 0.3 magnitude photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from non-stellar objects. USNO-B is now followed by NOMAD; both can be found on the Naval Observatory server. The Naval Observatory is currently working on B2 and C variants of the USNO catalogue series. GSC The Guide Star Catalog is an online catalogue of stars produced for the purpose of accurately positioning and identifying stars satisfactory for use as guide stars by the Hubble Space Telescope program. The first version of the catalogue was produced in the late 1980s by digitizing photographic plates and contained about 20 million stars, out to about magnitude 15. The latest version of this catalogue contains information for 945,592,683 stars, out to magnitude 21. The latest version continues to be used to accurately position the Hubble Space Telescope. PPM The PPM Star Catalogue (1991) is one of the best, both in the proper motion and star position till 1999. Not as precise as the Hipparcos catalogue but with many more stars. The PPM was built from BD, SAO, HD and more, with sophisticated algorithm and is an extension for the Fifth Fundamental Catalogue, "Catalogues of Fundamental Stars". HIP The Hipparcos catalogue was compiled from the data gathered by the European Space Agency's astrometric satellite Hipparcos, which was operational from 1989 to 1993. The catalogue was published in June 1997 and contains 118,218 stars; an updated version with re-processed data was published in 2007. It is particularly notable for its parallax measurements, which are considerably more accurate than those produced by ground-based observations. Gaia catalogues The Gaia catalogues are based on observations made by the Gaia space telescope. They are released in stages that contain increasing amounts of information; the early releases also miss some stars, especially fainter stars located in dense star fields. Data from every data release can be accessed at the Gaia archive. Gaia DR1, the first data release based on 14 months of observations made through September 2015, took place on 13 September 2016. The data release includes positions and magnitudes in a single photometric band for 1.1 billion stars using only Gaia data, positions, parallaxes and proper motions for more than 2 million stars based on a combination of Gaia and Tycho-2 data