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http://adc.gsfc.nasa.gov
http://cdsweb.u-strasbg.fr

   The Hipparcos and Tycho data were created by the European Space
Agency,  and are used here by permission.

   The source for faint stars is the Hubble Guide Star Catalog,
distributed by the Space Telescope Science Institute. This dataset
was originally intended to support precise pointing of the Hubble
Space Telescope.  The Guide Star Catalog (GSC) is copyrighted by the
Association of Universities for Research in Astronomy (AURA),  and is
reproduced here by permission.  The scientific efforts leading to the
production of the Guide Star Catalog are described in Volume 99,  pp
2019-2154 of the Astronomical Journal,  and in text files on the CD-ROM
version of the GSC from which data contained herein were extracted.
Those text files are also on this CD in the TABLES subdirectory.
                                                 
   The PGC (Principal Galaxy Catalog) was obtained from the Universite de
Lyon.  It was compiled by G. Paturel and L. Bottinelli of the Observatoire
de Paris,  and forms the basis for displaying galaxies at detailed levels.
                                                
   The RC3 (Third Revised Catalog of Galaxies) was obtained from Dr.
Harold Corwin,  at the California Institute of Technology.  It was
compiled by G. and A. de Vaucouleurs,  H. G. Corwin,  R. J. Buta,  G.
Paturel,  and P. Fouque.  With the PGC,  it is largely responsible for
the great improvements in the accuracy and quantity of data provided
for galaxies.

   The primary source for data on NGC and IC objects comes from Wolfgang
Steinicke's list on the NGC-IC Project Web site,  www.ngcic.org,  used
by permission here.

   Comments on many NGC and IC objects were supplied by Steve Coe, who
kindly gave permission for extracts from his observing notes to be shown
in "more info".

   Additional NGC and IC data comes from the Saguaro Astronomy Club. The
members of this club did an enormous amount of work in cleaning up many
errors in the RNGC and NGC2000 catalogs in the course of producing this
work,  and I am very happy to be able to make use of the results.

   Nebula catalogs have long been a major problem for Guide; the Nebula
Databank and isophotes created by Eric-Sven Vesting have almost
completely reversed this bad situation,  allowing Guide to provide
accurate information (and shapes) for all major nebulae and most minor
ones.  This tends to be very time-consuming labor,  and a lot of hours
were expended to check and cross-reference catalogs,  and in extracting
nebula isophotes from RealSky data.

   The Nebula Databank and isophote data are copyrighted by Eric-Sven

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