Dark nebulae, sometimes called absorption nebulae, are dust clouds free of nearby stars that rather than emitting or reflecting light absorb it and block our view of objects that lie beyond. They range from small black voids only a few arcminutes across to the Great Rift which spans more than 100 degrees and is easily visible with the naked eye in the summer Milky Way.
Telescopic dark nebulae have been observed for over two centuries, but no one was able to interpret their true nature. This situation lasted until the early 1900s, when Edward Barnard, a professor at the University of Chicago photographed and studied selected regions of the Milky Way and gradually came to believe that its many dark lanes where regions of obscuring dust and gas. His monumental work, the “Photographic Atlas of Selected Regions of the Milky Way” can be found online at the Georgia Tech website.
After this quick introduction, it is time to test your observing skills on a beautiful dark nebula that lies inside a well known Messier object, the Trifid Nebula.
This nebula is a popular object among deep sky observers, but few realize that the Trifid’s celebrated dark lanes are catalogued as Barnard 85. These dark nebulae are well seen in a 6-inch telescope at moderate power, and appear detailed in instruments of 8 inches or more aperture. Some observers report detecting them even with 3-inch scopes on clear nights with steady seeing.
If you don’t manage to see the three dark lanes on the first try, come back another night. Observing dark nebulae takes patience and sky darkness is critical regardless of your telescope.
Finder map – field width 15 degrees, stars to magnitude 8.5.