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).