About the NGC 2000.0 entries
NGC 2000.0 is a modern compilation of the New General Catalogue of Nebulae and Clusters of Stars (NGC), the Index Catalogue (IC), and the Second Index Catalogue compiled by J. L. E. Dreyer (1888, 1895, 1908). The new compilation of these classical catalogs is intended to meet the needs of present-day observers by reporting positions at equinox 2000.0 and by incorporating the corrections reported by Dreyer himself and by a host of other astronomers who have worked with the data and compiled lists of errata. The object types given are those known to modern astronomy.
This material is available both as a book (Sinnott 1988) and in machine-readable form (on a CD-ROM), available from the National Space Science Data Center (NSSDC). The following text has been edited by Malin from the documentation supplied with the CD-ROM version of NGC 2000.0. I am grateful to the publishers, Sky Publishing Corporation, and the NSSDC for permission to use extracts from the catalogue, and some of the introductory material below.
The editing (and the addition of a simple diagram) is intended to simplify access to the explanatory notes to the catalogue entries, however, the serious user is strongly recommended to consult the original work (Sinnott 1988) and the introductory text to the CD-ROM for much additional information and background.
David Malin, January 1, 1998
NGC 2000.0 (Edited by R.W. Sinnott 1988) Documentation for the Computer-Readable Version Wayne H. Warren Jr. December 1989 Doc. No. NSSDC/WDC-A-R&S 89-29 National Space Science Data Center (NSSDC)/ World Data Center A for Rockets and Satellites (WDC-A-R&S) National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt, MD 20771 Abstract The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described [in full, in the original documentation]. NGC 2000.0 is a modern version of the NGC and IC catalogs compiled by J. L. E. Dreyer in the late nineteenth and early twentieth centuries. Errata compiled by Dreyer and by subsequent workers have been incor- porated into the new version and the object types have been updated with information from modern astronomy; the descriptions given are those of Dreyer. The order of the new catalog is strictly by right ascension, the NGC and IC objects being merged into one machine- readable file. Introduction NGC 2000.0 is a modern compilation of the New General Catalogue of Nebulae and Clusters of Stars (NGC), the Index Catalogue (IC), and the Second Index Catalogue compiled by J. L. E. Dreyer (1888, 1895, 1908). The new compilation of these classical catalogs is intended to meet the needs of present-day observers by reporting positions at equinox 2000.0 and by incorporating the corrections reported by Dreyer himself and by a host of other astronomers who have worked with the data and compiled lists of errata. The object types given are those known to modern astronomy. This document describes [some aspects] of the machine-readable version of NGC 2000.0 as it is currently being distributed from the Astronomical Data Center (ADC). It includes descriptions of the data and format of the computerized version so that users of the file can process the data without problems and guesswork. It is, however, not intended to replace the source reference, which gives much more complete information regarding the compilation of the modern version, sources of the corrections incorporated into the file, information about the object descriptions used and their abbreviations, nomenclature, and statistics of object locations according to constellation. All users of the machine version are urged to acquire a copy of the published book in order to have complete information at their disposal. However, a copy of this document should be transmitted to any recipient of the machine-readable catalog. [The original] catalog is copyrighted by Sky Publishing Corporation, which has kindly deposited the machine version in the data centers for permanent archiving and dissemination to astronomers for scientific research purposes only. The data should not be used for commercial purposes without the explicit permission of Sky Publishing Corporation. Explanation of the NGC 2000.0 entries (explained in full below) Object ID Object number in the form "NGC nnnn" for NGC objects, and "IC nnnn" for IC objects, where "nnnn" indicates the sequential number of the object. Object type An object classification according to modern astronomy. The field is coded according to the following abbreviations: Gx Galaxy OC Open star cluster Gb Globular star cluster, usually in the Milky Way Galaxy Nb Bright emission or reflection nebula Pl Planetary nebula C+N Cluster associated with nebulosity Ast Asterism or group of a few stars Kt Knot or nebulous region in an external galaxy *** Triple star D* Double star * Single star ? Uncertain type or may not exist blank Unidentified at the place given, or type unknown - Object called nonexistent in the RNGC (Sulentic and Tifft 1973) PD Photographic plate defect Equatorial coordinates Equinox 2000. Data source code A letter code to indicate the source of modern data about the object. These citations will be found in the source reference, pages XXIII-XXIV, along with additional information. "Modern" data may include type, position, size, and magnitude, but not descriptions, which are always those of Dreyer. Constellation Constellation in which the object is located. Upper limit character The character "<" is present if object size is an upper limit. Object size Angular size in arcmin, as measured along the greatest dimension. This field can be blank if size is not reported. Magnitude Integrated (total) magnitude of the type indicated by the code in the following field. The precision varies as in the size field. Magnitude code Blank if the integrated magnitude is visual, "p" if it is a photographic (blue) magnitude. Description A description of the object, as given by Dreyer or corrected by him, in a coded or abbreviated form. For an NGC object, the description is always a visual impression, while the IC descriptions are often based on photographic appearance. A full list of the abbreviations will be found in Table II of the introduction to the published catalog (the source reference). Remarks and Modifications It is important, even for users of the machine-readable catalog and this documentation, to also have a copy of the published book. In addition to the tables and reference sources mentioned in this document, the book provides an introductory section with a brief history of the NGC and IC catalogs, a count of objects by constellation, information on Dreyer's descriptions, a table cross index of Messier and NGC/IC designations, and a table of common names for NGC objects. The book also contains a table of right ascensions for NGC and IC objects. References Dreyer, J. L. E. 1888, New General Catalogue of Nebulae and Clusters of Stars, Mem. Roy. Astron. Soc. 49, Part I (reprinted 1953, London: Royal Astronomical Society). Dreyer, J. L. E. 1895, Index Catalogue of Nebulae Found in the Years 1888 to 1894, with Notes and Corrections to the New General Catalogue, Mem. Roy. Astron. Soc. 51, 185 (reprinted 1953, London: Royal Astronomical Society). Dreyer, J. L. E. 1908, Second Index Catalogue of Nebulae Found in the Years 1895 to 1907; with Notes and Corrections to the New General Catalogue and to the Index Catalogue for 1888 to 1894, Mem. Roy. Astron. Soc. 59, Part 2, 105 (reprinted 1953, London: Royal Astronomical Society). NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer, ed. R. W. Sinnott 1988 (Sky Publishing Corporation and Cambridge University Press). Sulentic, J. W. and Tifft, W. G. 1973, The Revised New General Catalogue of Nonstellar Astronomical Objects (Tucson: The University of Arizona Press).