Astronomical catalog

Lists or enumerations of astronomical data, generally ordered by increasing right ascension of the objects listed. Astronomical catalogs vary a great deal in form and content depending upon their use, which may be purely astronomical, or for navigation, time determination, geodesy, or space science applications. In some catalogs the essential data are stellar positions and motions, while in others astrophysical data, such as magnitudes, spectra, and radial velocities of stars, are important. There are also catalogs of special stellar and of nonstellar objects. See also Astronomical coordinate systems.

A catalog regarded as the best representation of the celestial coordinate system at the time of its publication is called a fundamental star catalog.

The Fifth Fundamental Catalogue, designated FK5, was published by the Astronomisches Rechen-Institut in Heidelberg, Germany, in 1988. The catalog contains the positions (right ascensions and declinations) and their changes with time (proper motions and precession) of the 1535 stars in FK4, and an additional 3117 stars, down to an apparent visual magnitude of about 9.5. These catalogs, and other modern catalogs, have the standard epoch J2000.0, which is the date January 1, 2000, at 12 hours Universal Time.

The positions and proper motions of the stars in FK5 provide a fundamental system for measurements of other star positions and proper motions, which may be carried out for a variety of problems arising in stellar astronomy.

Moderately bright stars (seventh to ninth magnitude), selected on the basis of one star per square degree of the sky, are related to the fundamental system by meridian circle observations. These stars form a system of sufficient density to serve as position references for photographic observations. Typical of catalogs of such reference stars is the International Reference System (IRS) catalog covering the entire sky from pole to pole with one star per square degree. It is the current world standard reference system.

A photographic survey of the northern celestial hemisphere resulted in the AGK3 (Dritter Astronomische Gesellschaft Katalog, 1975), the third in a series of catalogs published by the German Astronomical Society. A revised version of this catalog has been published by the Astronomisches Rechen-Institut in Heidelberg as the Position and Proper Motion (PPM) Catalog of 181,731 stars north of −2.5° declination. A similar photographic catalog for the southern celestial hemisphere with plates taken at the Royal Cape Observatory in South Africa is the Second Cape Photographic Catalog (CPC2), published in 1970. It contains the positions of 250,000 stars.

An important photographic catalog covering the entire sky to a limiting magnitude of 13 is the result of an international undertaking involving 19 observatories, with each assigned zones of declination and observing with nearly identical telescopes. The catalog, known as the Carte du Ciel (CdC) or Astrographic Catalogue (AC), finally completed for all zones in 1964, provides the positions of the stars in the form of rectangular coordinates, as measured on the plates.

Among the numerous catalogs of astrophysical data is the monumental Henry Draper Catalog (HD) of spectral classification, which with its extension includes data for 275,000 stars published in 10 volumes. The general acceptance of the U, B, V photometric system since its inception in the 1950s is shown by the compilation of a general catalog containing data for 87,000 stars (Astronomy and Astrophysics, suppl., vol. 71, 1987).

L. E. Dreyer's New General Catalogue of Nebulae and Starclusters (1888) contains the objects originally classified as nonstellar, with galaxies included as nebulae. The catalog contains 7840 objects, and was supplemented by two index catalogs in 1895 and 1908 with an additional 5386 objects. The NGC and IC numbers assigned in these catalogs remain the most commonly used designations. See also Nebula; Star clusters; Variable star.

Since Dreyer's time, the number of known nonstellar optical objects has increased by an order of magnitude, and the data are scattered through the astronomical literature. R. S. Dixon and G. Sonneborn compiled A Master List of Nonstellar Astronomical Objects (1980) with approximately 185,000 listings from 270 catalogs, with multiple listings of objects appearing in several catalogs.