Barnard's initial catalog of dark nebulae, first published in 1919, described 182 entries and was superceded by a 1927 follow-up publication which was expanded to include 349 entries.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: This impressive object is characterized as a nebula with an embedded cluster. The nebula portion is dominated by the Barnard dark nebula catalogued as B175 which runs vertically and with an apparent length of approximately 60 arc-minutes. At the northernmost tip of B175 lies the reflection nebula vdB 152 measuring three arc-minutes in diameter and illuminated by the bright star BD+69°1231 (mag 8.8). The open cluster OCL 252.1 embedded within the nebulosity is comprised of less than 50 member stars lying at a distance of 1400 light-years away. The object is generally known as vdB 152 and in spite of the very dominant and dense dark nebula within the field of view.