This directory contains a set observing lists that have been optimized for
particular telescope sizes.  Each list contains objects that are
theoretically visible in a given telescope under a dark sky.  The object
data comes from the SAC 6.0 database (currently on ftp.seds.org in
/pub/astro/catalogs/SAC/) that has been run through the sacodm program
(also on seds in /pub/software/pc/obsprog/odmv11b.zip) and then massaged
slightly for usability.

The latest versions of the lists are on ftp.seds.org, in the
/pub/astro/catalogs/optimized directory.

This is version 1.1 of the lists, and includes a correction to the Messier
object list in Appendix B.  In the original version, a transcription error
resulted in mismatched descriptive text for M77 through M110.

The following is the introductory text for the 50mm object list:

                       Optimized Deep-Sky Object List

		Telescope Aperture: 50mm
		Background Surface Brightness: 22 mag/sq arcsecond

     Introduction

       This list of deep sky objects has been optimized for a 50mm
     telescope under a fairly dark sky.  Other versions of this list have
     been generated for telescopes ranging in size from 50mm to 24 inches.
     Each list is prominently labeled to indicate the telescope and sky
     conditions for which it was generated.

            The following fields are included in the list:

                 Object   - the NGC number or other identifier
                 Type     - galaxy, open cluster, globular cluster, etc
                 Con      - The constellation.  See Appendix A for a list
                            of abbreviations.
                 R.A.     - Right Ascension (year 2000)
                 Dec      - Declination (year 2000)
                 Mag      - magnitude
                 Size     - dimensions in minutes (') or seconds ('') of arc
                 Con Diff - The difference between the log of the contrast
                            threshold and the log of the contrast of the
                            object.  See below for more information.
                 ODM      - Optimum detection magnification

       The Con Diff field gives an indication of the visibility of the
     object, and depends on the object size and magnitude, and the
     telescope aperture and sky conditions.  It is based on the calculations
     that are presented in "Visual Astronomy of the Deep Sky" [1], and is
     derived by subtracting the log of the contrast threshold for the
     conditions from the log of the contrast level of the object.  A
     negative value indicates that the object is not visible (these
     objects are excluded from the list), and an increasingly positive
     number indicates increasing visibility.  An object with a Con Diff
     field of 1.0 or higher should be fairly easy for an experienced
     observer.  An object with a Con Diff field below about 0.3 will
     probably be extremely difficult for all but the most experienced
     observers.

       The ODM field indicates the optimum magnification that should be
     used to detect the object.  This field is also derived from
     calculations in "Visual Astronomy of the Deep Sky."  You may notice
     that some of these values are incredibly high (ridiculously?).  These
     objects are included in the list because there is no theoretical
     limit to the amount of magnification that can be applied in order to
     detect them.  If you feel ambitious, give them a try with as much
     power as you can muster.

       The data for this catalogue comes from the Saguaro Astronomy Club
     (SAC) version 6.0 Deep Sky Database [2].  The data was run through
     the sacodm program [3], then massaged into its current format.  All
     data for objects that did not include enough information for the
     required calculations has been removed.

       The catalogue has been sorted by constellation, then by Right
     Ascension within each constellation.

       Appendix A contains a list of abbreviations that are used within
     the list to identify constellation names.

       Appendix B contains a list Messier objects, and indicates the
     catalogue ID used within the main list, the object type,
     constellation name, chart number in Sky Atlas 2000.0, and page
     number in Visual Astronomy of the Deep Sky.  The last field
     contains the object description from the SAC 6.0 database.

     [1] Clark, Roger N., "Visual Astronomy of the Deep Sky", 
     1990, Sky Publishing Corporation, ISBN  0-933-346-54-9,
     and  Cambridge  University Press, ISBN 0-521-36155-9.

     [2] Saguaro Astronomy Club, SAC 6.0 Database,
     ftp://ftp.seds.org/pub/astro/catalogs/SAC/

     [3] Lutz, David L., sacodm,
     ftp://ftp.seds.org/pub/software/pc/obsprog/odmv11b.zip

     This object list is copyright 1997,1999 by David L. Lutz.

To reach the author, send mail to David.Lutz@East.Sun.COM.