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.