The New General Catalogue of Nebulae and Clusters of Stars (NGC) is an extensive catalogue of astronomical deep sky objects that was compiled by John Louis Emil Dreyer in 1888. Danish born Dreyer spent much of his life in Ireland where he compiled the catalogue, which was based on Sir William Herschel's Catalogue of Nebulae and Clusters of Stars.
Herschel first published his catalogue containing 1,000 entries in 1786 with assistance from his sister Caroline. He then added another 1,000 entries in 1789 and a final 500 in 1802, bringing the total number of entries to 2,500. In 1864, Sir John Herschel the son of William then expanded the catalogue into the General Catalogue of Nebulae and Clusters and Clusters of Stars (GC), which contained 5,079 entries.
Dreyer build on the early work of the Herschel's to produce the renowned NGC, which is still used by astronomers all over the World today. In total he listed 7,840 objects that are referred to as NGC objects. The catalogue contains all types of deep sky objects including galaxies, nebulae, globular clusters, open clusters, supernova remnants and planetary nebulae. Compiling the catalogue was a massive task for Dreyer, he had to deal with many observation reports from a host of different scopes that contained numerous amounts of contradictory information. The sheer volume of information and number of objects meant Dreyer couldn't validate all of them himself and as a result, he had to accept some data as recorded. Although Dreyer himself was very accurate in his transcripts, it's perhaps not surprising that the catalogue contains several, mostly position and description errors.
In addition to the NGC, Dreyer also published two supplements, known as the Index Catalogues (IC). The first containing 1,520 objects was published in 1895. The second published in 1908 listed an extra 3,866 objects. In total, the two IC's catalogues contain 5,386 objects.
Various attempts have been made to correct the original NGC errors. These include the Revised New General Catalogue by Jack Sulentic and William Tifft in 1973 and NGC 2000.0 by Roger Sinnott in 1989 using J2000.0 coordinates. More recently, the Revised New General Catalogue and Index Catalogue (Revised NGC/IC) published by Wolfgang Steinicke in 1996.