The General Catalog of Variable Stars (GCVS) is the only reference source on all known variable stars. This database is based on the electronically-readable version as distributed by the Sternberg Astronomical Institute and Institute of Astronomy (Russian Acad. Sci.), Moscow. It is the catalog of extragalactic variable stars, an updated version of the list contained in the GCVS (4th edition), Volume V. The total number of entries in this database is 10979 variable stars in 35 stellar systems (including the Magellanic Clouds, the Andromeda Galaxy, etc.). These variables include 144 stars now considered to be non-members of the galaxies in whose fields they lie, and 92 more stars that are possible non-members. The present improved electronic version of the GCVS 4th Edition, Volumes I-V, combined with the Name-Lists of Variable Stars Nos. 67 - 77, is also available from the Sternberg Institute via anonymous ftp to ftp://ftp.sai.msu.su/pub/groups/cluster/gcvs/gcvs/ and more information is available via the Web at http://www.sai.msu.su/groups/cluster/gcvs/gcvs/. This online version of the GCVS Vol. V Catalog of Extragalactic Variable Stars was created by the HEASARC in January 2005 based on CDS Catalog II/250, table evs_cat.dat. The latter was itself based on on an electronically-readable version that was distributed by the Sternberg Astronomical Institute and Institute of Astronomy (Russian Acad. Sci.), Moscow. This is a service provided by NASA HEASARC .

Work aimed at compiling detailed catalogs of variable stars in the Galaxy, which has been carried out continuously by Moscow variable-star researchers since 1946 on behalf of the International Astronomical Union, has entered the stage of the publication of the 5th, completely electronic edition of the General Catalog of Variable Stars (GCVS). The GCVS 5.1 is freely accessible on the Internet. The authors recommend citing their paper as a unified reference to the 5th edition of the GCVS. The GCVS is the only reference source on all known variable stars. This version contains the electronically-readable version as distributed by the Sternberg Astronomical Institute and Institute of Astronomy (Russian Acad. Sci.), Moscow. After the publication of Volume III of the 4th edition of the GCVS, the subsequent Name-lists with numbers from 67 to 77 contained only names of variable stars in the GCVS systems, together with their coordinates and variability types. The authors actually started compiling the 5th edition of the GCVS ten years ago, with the 78th Name-list of Variable Stars, which provided (as did all subsequent Name-lists) complete GCVS information for each star (in addition to the variability types, ranges of brightness variations, epochs of brightness maxima or minima, periods, etc.). In all, the 78th-81st Name-lists contain more than 13300 variable stars. The complete revision of information on the coordinates of variable stars (see the Introduction section of the reference paper) was also a part of the transition to the 5th edition. The present electronic version of the GCVS5.1 is available from Sternberg Astronomical Institute (Lomonosov Moscow University) and Institute of Astronomy (Russian Academy of Sciences) at http://www.sai.msu.su/gcvs/gcvs/ as a first release of the fifth GCVS edition. Information on the contents and principles of the fifth edition can be found in Samus et al. (2017), the official reference to GCVS 5.1. The GCVS 5.1 version contains data for individual variable objects discovered and named as variable stars by 2021 and located mainly in the Milky Way galaxy. The total number of named variable stars, not counting designated non-existing stars or stars subsequently identified with earlier-named variables, is now 58035. The stars of the GCVS 5.1 are stars of the GCVS fourth edition plus Name-lists Nos. 67-84. The stars from the Name-lists Nos.78-84 are presented in the complete GCVS format. Complete information for stars of the Name-lists Nos. 67-77 is so far provided in the first 20 constellations (Andromeda to Cepheus). In these constellations, the GCVS information has been completely revised with active use of new publications as well as observations retrieved by the GCVS compilers by data mining and used to determine new variability types and new light elements whenever possible. The authors are continuing this work and will introduce new data for the next constellations as soon as they are ready. This version of the GCVS catalog was last updated by the HEASARC in September 2022, based on the file at http://www.sai.msu.su/gcvs/gcvs/gcvs5/gcvs5.txt. This is a service provided by NASA HEASARC .

The Uppsala General Catalogue of Galaxies (UGC) is an essentially complete catalog of galaxies to a limiting diameter of 1.0 arcminute and/or to a limiting apparent magnitude of 14.5 on the blue prints of the Palomar Observatory Sky Survey (POSS). Coverage is limited to the sky north of declination -02.5 degrees. Galaxies smaller than 1.0 arcminute in diameter but brighter than 14.5 mag may be included from the Catalogue of Galaxies and of Clusters of Galaxies (CGCG, Zwicky et al. 1961-1968); all such galaxies in the CGCG are included in the UGC. The galaxies are numbered in order of their 1950.0 right ascension values. The catalog contains descriptions of the galaxies and their surrounding areas, plus conventional system classifications and position angles for flattened galaxies. Galaxy diameters on both the blue and red POSS prints are included and the classifications and descriptions are given in such a way as to provide as accurate an account as possible of the appearance of the galaxies on the prints. Only the data portion of the published UGC is included in the machine-readable version, notice. For additional details regarding the classifications, measurement of apparent magnitudes, and data content, the source reference should be consulted. This database table was first ingested by the HEASARC in September 2000 based on a machine-readable version of the UGC obtained from the ADC (ADC Catalog VII/26D). This latter version was a corrected and modified version of the original magnetic tape version of the UGC. A list of the types of changes and modifications made by the ADC is available at https://cdsarc.u-strasbg.fr/ftp/cats/VII/26D/ReadMe, while the list of the affected entries is available at https://cdsarc.u-strasbg.fr/ftp/cats/VII/26D/errors.dat.gz.

The HEASARC last updated this database table in November 2021 upon reflection that the original catalog's coordinates were B1950 (instead of J1950, as originally assumed by the HEASARC). Due to the precision of the coordinates in this catalog, the difference is negligible. This is a service provided by NASA HEASARC .