New General Catalogue

The NGC was compiled by Danish-Irish astronomer John Louis Emil Dreyer, who based it on observations from William Herschel and his son John Herschel, as well as other observers. Dreyer published it in 1888 as a supplement to the Memoirs of the Royal Astronomical Society, consolidating earlier catalogues such as the Herschel 500 and the General Catalogue of Nebulae. The catalogue's numbering system, which assigns each object a sequential NGC number, became the de facto standard for identifying deep-sky objects.²

The NGC includes a wide range of objects: galaxies, open and globular clusters, planetary nebulae, and diffuse nebulae. Each entry provides coordinates, magnitude, and a brief description. The catalogue is organized by right ascension, and its entries are often used with prefixes like "NGC" (e.g., NGC 224, the Andromeda Galaxy). The original catalogue was later supplemented by two Index Catalogues (IC I and IC II), adding over 5,000 more objects, bringing the total to over 13,000.³

Despite its age, the NGC remains the primary reference for deep-sky observers. However, errors in positions and descriptions have been identified, leading to the Revised New General Catalogue (RNGC) in 1973 and the NGC/IC Project, which aims to correct and update the data. The catalogue's enduring popularity stems from its comprehensive coverage and the historical significance of its objects, many of which are key targets for amateur telescopes.

One lesser-known fact is that the NGC includes a few objects that are not real, such as NGC 1820, which is a duplicate entry. Additionally, some entries are stars or asterisms, not true deep-sky objects. The catalogue also contains historical curiosities like NGC 604, a giant H II region in the Triangulum Galaxy, and NGC 6240, a merging pair of galaxies. The NGC/IC Project has identified over 1,000 errors in the original, highlighting the challenges of visual observation in the 19th century.

Deep-sky object

Any astronomical object outside the Solar System, such as galaxies, nebulae, and star clusters.

Right ascension

The celestial equivalent of longitude, used to locate objects on the sky.

H II region

A region of ionized hydrogen where star formation is occurring.