star catalog

a list of stars giving various characteristics: equatorial coordinates and their variations, stellar magnitudes, spectral classes, and the like. In addition to fundamental stellar characteristics, auxiliary ones are also given, which serve to identify stars in the sky with those in star catalogs. Stars in star catalogs are listed in order of increasing right ascension; the numbers under which stars are recorded are often used for their designation. Compiled on the basis of astronomical observations, star catalogs are the fundamental material for studying the structure and motions in stellar systems and for establishing a system of celestial coordinates that serves as the basis for solving problems in astrometry, geodesy, and celestial mechanics.

Star catalogs listing stars according to position (positional catalogs) have data sufficient to assign a mean equatorial system of celestial coordinates for a fixed epoch or to reproduce this system for an arbitrary epoch. Thus, a distinction is made between original catalogs, which give coordinates of stars derived directly from observations, and derived catalogs, which list coordinates of stars and their variations owing to proper motion and precession that are derived by combining many original catalogs. Original star catalogs are divided into absolute catalogs, which are compiled independently of any previous catalogs, and relative catalogs, in which the positions of stars are specified relative to the positions of a certain number of stars with already determined coordinates. An example of absolute star catalogs is the series of catalogs of bright stars regularly compiled at the Pulkovo Observatory (USSR) since its founding. Relative catalogs are, for example, the international zone catalogs of the German Astronomical Society, which contain all stars up to a magnitude of 9.0. Derived positional catalogs (fundamental and composite) make it possible to reproduce the system of mean equatorial coordinates for any epoch. This fact, as well as the high degree of accuracy of derived catalogs, enables them to be used as the geometric foundations for the solution of many problems in astronomy and allied sciences.

Fundamental star catalogs are the most precise positional catalogs and are compiled by combining absolute and relative catalogs for different epochs. An example of such a catalog is the most precise catalog of the mid-20th century—the Fourth Fundamental Catalog (FK4), the coordinate system of which is used as the basis in all astronomical yearbooks. The accuracy of the FK4 catalog, which contains 1,535 stars over the entire sky, is characterized by a mean square error of ±(0.02–0.03”) for the coordinates and ±(0.10–0.15”) for the proper motions of stars (per century). The error in the system of coordinates given by the FK4 catalog is of a similar order, but it increases with time because of the errors in the proper motions of the stars.

Composite star catalogs of positions are formed by combining relative catalogs, which are compiled from observations, for example, in a single epoch at several observatories in a common fundamental coordinate system to diminish random errors in the coordinates. In addition to coordinates, composite catalogs usually include proper motions, which are derived with the help of other sources. An example is the Catalog of Geodetic Stars compiled from observations at five Soviet astronomical observatories, which serves as a foundation for astronomical and geodetic determinations.

Following the suggestion of Soviet astrometers, work on an international level is being done on the compilation of a principally new Catalog of Faint Stars. In addition to obtaining a new fundamental coordinate system based on faint stars, it is also proposed that there be refinement of the stellar positions using observations of asteroids and proper motions of stars using observations of galaxies.

Surveys make up another group of star catalogs; these contain information on all stars up to a certain limit of magnitude and give their magnitudes and approximate coordinates. Thus, the Bonner Durchmusterung (BD) contains about 458,000 stars up to a magnitude of 9.5 from + 90° to -23° declination. This survey was continued for the southern sky by the Cordoba Durchmusterung (CD) and the Cape Photo-graphic Durchmusterung (CPD). The numbers of the stars in the BD, CD, and CPD catalogs are widely used for the designations of celestial bodies. Also in this category is the Henry Draper Catalog (HD) prepared by Harvard University, which includes the spectral classes and magnitudes of more than 300,000 stars. A photometric star catalog is the photoelectric catalog of stellar magnitudes and color indexes for more than 20,000 stars in the UBV system published in the mid-20th century and compiled by the Naval Observatory in Washington, D.C. (USA). Catalogs of radial velocities and stellar parallaxes, as well as catalogs of variable stars, double stars, and others, are also common—for example, the Index Catalog of Double Stars (IDS) of the Lick Astronomical Observatory (USA), which contains data on 64,000 stars. A large number of catalogs of various stellar characteristics are being compiled in connection with the detailed study of selected areas according to a plan of J. Kapteyn (Netherlands).