fundamental catalog

fundamental catalog

A catalog of fundamental stars in which the precise mean positions and proper motions of the stars are listed for a given epoch; positions are determined as accurately as possible by recording transit times across the meridian at several observatories. The inclusion of data from many different observatories worldwide and from earlier catalogs helps to minimize errors. Other star catalogs can be compiled by reference to a fundamental catalog. A series of German fundamental catalogs commenced publication with the First Fundamental Catalog, prepared by G.F.J.A. Auwers for the Astronomische Gesellschaft in Berlin in 1879. It incorporated contemporary observations with the best of earlier data. The Fourth Fundamental Catalog (Fundamentalkatalog 4 or FK4) and its successors were prepared and published in Heidelberg by the Astronomisches Rechen-Institut. FK4, published 1963, contains data for 1535 classic reference stars to a limiting magnitude of 7 for the epoch 1950.0. Information from some 300 earlier catalogs contributed to FK4's dataset. The Fifth Fundamental Catalog (FK5) was published in 1988. It contains improved data on the same stars and is based on the standard epoch J2000.0 (see Julian year); a supplement, FK5 Extension (FK5E), appeared in 1991, with data on an additional 3117 stars to magnitude 9.5. The Sixth Fundamental Catalog (FK6), which began publication in 1999, combines the results of the Hipparcos mission with the FK5 data. Parts I and III of FK6, which had appeared by the end of 2000, contain 878 fundamental stars and 3272 new stars respectively. The catalogs FK4 to FK6 are being made available in computerized form.

Fundamental Catalog


a star catalog that establishes a fundamental equatorial system of celestial coordinates with maximum precision.

A fundamental coordinate system provides the basis for the study of the motions of celestial bodies and for the determination of astronomical coordinates, time, and azimuth for points on the earth’s surface. Such a coordinate system is fixed by the set of data contained in a fundamental catalog. The data include mean equatorial coordinates—that is, right ascensions and declinations—for a selected epoch for a certain number of stars distributed uniformly over the celestial sphere; they also include changes in the coordinates resulting both from precession and from the proper motions of the stars. Such data make it possible to reconstruct a fundamental coordinate system for any epoch that differs from the epoch of the catalog.

Fundamental catalogs are compiled by combining many star catalogs and the results of observations made at various observatories at different epochs. The comparative analysis of original catalogs makes it possible to reduce the systematic and random errors in the data listed in fundamental catalogs. The zero points of the fundamental coordinate system—that is, the plane of the celestial equator and the position of the vernal equinox—are determined from observations of objects in the solar system. Observations of galaxies are used to refine the proper motions of the stars.

The fundamental coordinate systems in use today were developed as a result of three independent efforts that led to the compilation of several series of fundamental catalogs. These catalogs include the catalogs of S. Newcomb, which were intended for the determination of astronomical constants and the refinement of the theory of the motion of the major planets; the catalogs of L. Boss, which were used to study the Milky Way system; and the catalog of A. von Auwers, which was employed to compile catalogs of ninth-and tenth-magnitude stars.

The most precise fundamental catalog is the Fourth Fundamental Catalogue (FK4), which made use of Auwers’ work. In 1964, the FK4 was adopted as the international basis for astronomical almanacs and geodetic determinations. The FK4 contains 1,535 bright stars over the entire sky. The random error in the positions of the stars is characterized by a mean square error of ±(0.02–0.03”); the random error in the proper motions of the stars is characterized by a mean square error of ±(0.10–0.15”). The systematic error in the positions of the stars in the FK4 system is of a similar order. The accuracy is somewhat lower for southern stars than for northern stars.

The Boss General Catalogue of 33,342 Stars for the Epoch 1950 (GC) was widely used for stellar astronomical research. The accuracy of this catalog was greatly reduced by data of insufficient reliability on the proper motions of the stars.


Podobed, V. V., and V. V. Nesterov. Obshchaia astrometriia. Moscow, 1975.
Podobed, V. V. Fundamental’naia astrometriia. Moscow, 1968.


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