an Entity references as follows:
The Uppsala General Catalogue of Galaxies (UGC) is a catalogue of 12,921 galaxies visible from the northern hemisphere. It was first published in 1973. The catalogue includes essentially all galaxies north of declination -02°30' and to a limiting diameter of 1.0 arcminute or to a limiting apparent magnitude of 14.5. The primary source of data is the blue prints of the Palomar Observatory Sky Survey (POSS). It also includes galaxies smaller than 1.0 arcminute in diameter but brighter than 14.5 magnitude from the Catalogue of Galaxies and of Clusters of Galaxies (CGCG).