The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an

astronomical catalogue An astronomical catalog or catalogue is a list or tabulation of astronomical objects, typically grouped together because they share a common type, morphology, origin, means of detection, or method of discovery. The oldest and largest are star ca ...

deep-sky object A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed ...

s compiled by

John Louis Emil Dreyer John Louis Emil Dreyer (13 February 1852 – 14 September 1926) was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, England. Life Dreyer was born in Copenhagen. His fat ...

in 1888. The NGC contains 7,840 objects, including

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

star cluster Star clusters are large groups of stars. Two main types of star clusters can be distinguished: globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound, while open clusters are more loosely clust ...

s and

emission nebula An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission ...

e. Dreyer published two supplements to the NGC in 1895 and 1908, known as the ''Index Catalogues'' (abbreviated IC), describing a further 5,386 astronomical objects. Thousands of these objects are best known by their NGC or IC numbers, which remain in widespread use. The NGC expanded and consolidated the cataloguing work of

William William is a male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sex ...

and

Caroline Herschel Caroline Lucretia Herschel (; 16 March 1750 – 9 January 1848) was a German born British astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigolle ...

, and

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...

's ''

General Catalogue of Nebulae and Clusters of Stars The ''Catalogue of Nebulae and Clusters of Stars'' (CN) is an astronomical catalogue of nebulae first published in 1786 by William Herschel, with the assistance of his sister Caroline Herschel. It was later expanded into the ''General Catalogue o ...

''. Objects south of the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projecti ...

are catalogued somewhat less thoroughly, but many were included based on observation by

James Dunlop James Dunlop FRSE (31 October 1793 – 22 September 1848) was a Scottish astronomer, noted for his work in Australia. He was employed by Sir Thomas Brisbane to work as astronomer's assistant at his private observatory, once located at Parama ...

. The NGC contained multiple errors, but attempts to eliminate them were made by the ''Revised New General Catalogue'' (RNGC) by Jack W. Sulentic and William G. Tifft in 1973, ''NGC2000.0'' by Roger W. Sinnott in 1988, and the ''NGC/IC Project'' in 1993. A ''Revised New General Catalogue and Index Catalogue'' (abbreviated as RNGC/IC) was compiled in 2009 by Wolfgang Steinicke and updated in 2019 with 13,957 objects.

Original catalogue

The original ''New General Catalogue'' was compiled during the 1880s by

using observations from

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...

and his son

John John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...

, among others. Dreyer had already published a supplement to Herschel's ''

General Catalogue of Nebulae and Clusters A general officer is an officer of high rank in the armies, and in some nations' air forces, space forces, and marines or naval infantry. In some usages the term "general officer" refers to a rank above colonel."general, adj. and n.". OED On ...

'' (GC), containing about 1,000 new objects. In 1886, he suggested building a second supplement to the ''General Catalogue'', but the

Royal Astronomical Society (Whatever shines should be observed) , predecessor = , successor = , formation = , founder = , extinction = , merger = , merged = , type = NGO ...

asked Dreyer to compile a new version instead. This led to the publication of the ''New General Catalogue'' in the ''

Memoirs of the Royal Astronomical Society (Whatever shines should be observed) , predecessor = , successor = , formation = , founder = , extinction = , merger = , merged = , type = NG ...

'' in 1888. Assembling the NGC was a challenge, as Dreyer had to deal with many contradictory and unclear reports made with a variety of telescopes with apertures ranging from 2 to 72 inches. While he did check some himself, the sheer number of objects meant Dreyer had to accept them as published by others for the purpose of his compilation. The catalogue contained several errors, mostly relating to position and descriptions, but Dreyer referenced the catalogue, which allowed later astronomers to review the original references and publish corrections to the original NGC.

''Index Catalogue''

The first major update to the NGC is the ''Index Catalogue of Nebulae and Clusters of Stars'' (abbreviated as ''IC''), published in two parts by Dreyer in 1895 (IC I, containing 1,520 objects) and 1908 (IC II, containing 3,866 objects). It serves as a supplement to the NGC, and contains an additional 5,386 objects, collectively known as the IC objects. It summarizes the discoveries of galaxies, clusters and nebulae between 1888 and 1907, most of them made possible by

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed i ...

. A list of corrections to the IC was published in 1912.

''Revised New General Catalogue''

The ''Revised New Catalogue of Nonstellar Astronomical Objects'' (abbreviated as ''RNGC'') was compiled by Jack W. Sulentic and William G. Tifft in the early 1970s, and was published in 1973, as an update to the NGC. The work did not incorporate several previously-published corrections to the NGC data (including corrections published by Dreyer himself), and introduced some new errors. For example, the well-known compact galaxy group

Copeland Septet The Copeland Septet (also Copeland's Septet, Hickson Compact Group 57) is a group of galaxies in the constellation Leo that includes NGC 3748, NGC 3754, NGC 3750, NGC 3751, NGC 3745, NGC 3753 and NGC 3746. The group was discovered by Briti ...

in the Leo constellation appears as non-existent in the RNGC. Nearly 800 objects are listed as "non-existent" in the RNGC. The designation is applied to objects which are duplicate catalogue entries, those which were not detected in subsequent observations, and a number of objects catalogued as star clusters which in subsequent studies were regarded as coincidental groupings. A 1993 monograph considered the 229 star clusters called non-existent in the RNGC. They had been "misidentified or have not been located since their discovery in the 18th and 19th centuries". It found that one of the 229—NGC 1498—was not actually in the sky. Five others were duplicates of other entries, 99 existed "in some form", and the other 124 required additional research to resolve. As another example,

reflection nebula Reflection or reflexion may refer to: Science and technology * Reflection (physics), a common wave phenomenon ** Specular reflection, reflection from a smooth surface *** Mirror image, a reflection in a mirror or in water ** Signal reflection, in s ...

NGC 2163 in Orion was classified "non-existent" due to a transcription error by Dreyer. Dreyer corrected his own mistake in the Index Catalogues, but the RNGC preserved the original error, and additionally reversed the sign of the declination, resulting in NGC 2163 being classified as non-existent.

''NGC 2000.0''

''NGC 2000.0'' (also known as the ''Complete New General Catalog and Index Catalog of Nebulae and Star Clusters'') is a 1988 compilation of the NGC and IC made by Roger W. Sinnott, using the

J2000.0 In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to pert ...

coordinates. It incorporates several corrections and errata made by astronomers over the years.

NGC/IC Project

The NGC/IC Project is a collaboration among professional and amateur astronomers formed in 1993. Completed by 2017, it aimed to identify all NGC and IC objects, correct mistakes, collect images and basic astronomical data. Primary team members were Harold G. Corwin Jr., Steve Gottlieb, Malcolm Thomson, Robert E. Erdmann and Jeffrey Corder.

''Revised New General Catalogue and Index Catalogue''

The ''Revised New General Catalogue and Index Catalogue'' (abbreviated as ''RNGC/IC'') is a compilation made by Wolfgang Steinicke in 2009. It is a comprehensive and authoritative treatment of the NGC and IC catalogues.

References

External links

The Interactive NGC Catalog Online

Adventures in Deep Space: Challenging Observing Projects for Amateur Astronomers.

Revised New General Catalogue
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