Barnard's initial catalog of dark nebulae, first published in 1919, described 182 entries and was superceded by a 1927 follow-up publication which was expanded to include 349 entries. These "dark nebulae" are believed to be the result of molecular clouds of dust and gas which are present in our line of sight and which absorb the starlight originating behind them, thus providing the earth-based observer working in the visible spectrum the illusion of a black "void" (these dark nebulae are NOT associated with dark matter!). Some of the best-known examples of these "absorption nebulae" include B33 (Horsehead Nebula), B68 (Molecular Cloud 68), B72 ("S" or Snake Nebula) and B142-143 ("E" Nebula).

Note: One of the densest Barnard dark nebulae is B92 in Sagittarius and which is often nicknamed "Black Hole". It runs vertically measuring approximately 15 arc-minutes north-south and nine arc-minutes east-west. It is estimated to lie 650 light-years away although some sources suggest even 10,000 light-years away. Its companion (dark) nebula lying less than one-half degree away to the east is B93 whose apparent size is 15 arc-minutes vertically and only two arc-minutes wide with similar density as B92. Both B92 and B93 lie within the M24 star cloud and which makes their density very noticeable and apparent.

Note: The second image below annotates the presence of the dwarf planet Pluto which was traversing through the M24 Star Cloud in Sagittarius during the summer of 2010.

Note: The image below was characterized with a very dominant light gradient which adversely affected the final result. It will be revisted under darker skies at the first available opportunity.