A near-complete inventory of the galaxies in our northern sky

Space · Published 17 October 2026 Swipe more like this →

In short: Mapping the cosmos requires a starting point. The Uppsala General Catalogue of Galaxies (UGC) provides an essentially complete record of galaxies visible from the northern hemisphere, capturing the vast architecture of our universe on a single, systematic scale.

First published in 1973, the UGC serves as a foundational astronomical reference. The Palomar Observatory Sky Survey (POSS) blue prints serve as the basis for its galaxy listings. To ensure comprehensive coverage, the catalog includes galaxies with a limiting diameter of 1.0 arcminute or an apparent magnitude of 14.5 on those blue prints. Its reach is primarily restricted to the sky north of a declination of -02.5 degrees. Zwicky et al. compiled the Catalogue of Galaxies and of Clusters of Galaxies, which is featured in this list. between 1961 and 1968. This ensures that smaller but bright objects are not overlooked. The entries are organized numerically based on their 1950.0 right ascension values.

The catalog is not just a list of coordinates; it is a descriptive record. It provides conventional system classifications, position angles for flattened galaxies, and detailed descriptions of the galaxies and their surrounding areas. To maintain accuracy, the entries were designed to reflect the appearance of galaxies as they actually appeared on the POSS prints. Measurements for the diameters of galaxies appear for both red and blue POSS prints within the data. These records aim to provide the most accurate account possible of the galaxies' visual appearance. This level of detail helps astronomers understand the physical orientation of these distant structures.

Additionally, every CGCG entry with a brightness exceeding 14.5 magnitude and a size under 1.0 arcminute is integrated. The data has undergone significant curation over decades. The machine-readable version used by NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) was first ingested in September 2000. The ADC supplied a revised and updated iteration of the initial magnetic tape for this edition. A notable correction occurred in November 2021 when researchers realized the original coordinates were B1950 rather than J1950, though the difference was deemed negligible due to the catalog's specific precision requirements. The machine-readable version currently available only contains the data portion of the published work. This specific dataset was obtained from the ADC Catalog VII/26D. A separate addendum, known as the UGCA, contains an additional 444 galaxies.

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