These
dark nebulae are usually seen as silhouettes against a brighter background.
Get familiar with compilations of nebulae, like the Sharpless (Sh) and van den Bergh (vdB) catalogs, as well as Lynd's Bright Nebulae (LBN) and Lynd's
Dark Nebulae (LDN).
Barnard catalogued it as B33 in his list of
dark nebulae published in a 1919 paper in the Astrophysical Journal, where he notes 'Dark mass, diam 4', on nebulous strip extending south from zeta Orionis'.
Several
dark nebulae can be seen in the constellation, but as we know by now, light pollution stops us from seeing many wonderful objects, which can be found only in ideal dark star-filled night sky conditions.
Indeed, the bright, compact, red objects seen in some of these infrared dark clouds mark the locations of dust cocoons warmed by the light of newborn stars enshrouded in these
dark nebulae.
The gases and dust that crisscross the Trifid Nebula make up the third kind of nebula in this cosmic cloud, known as
dark nebulae, courtesy of their light-obscuring effects.
I love
dark nebulae. Seeing these clouds of interstellar dust silhouetted against a rich star field gives the Milky Way a three-dimensional appearance and makes the galaxy look that much more real.
Dark nebulae consist of clouds of gas and dust that are not so illuminated, giving the cloud the appearance of a region devoid of stars.
Dark nebulae exemplify the mind-bending reality of the inner Milky Way: The darkness is a thing, clouds of dust in the foreground of our view, and the bright blaze of the galaxy mostly represents the more distant swarms of stars that populate the inner spiral arms and galactic bulge.
Of course when looking at objects in the Milky Way, these are mostly fairly close, and there are a wide range of objects to be seen with a telescope--planetary nebulae, bright nebulae,
dark nebulae and supernova remnants, and here are just a few suggestions of objects to look at in these categories.
Object Type RA (J2000.0) Dec eta Chamaeleontis Open Cluster 08h41.3 -78[degrees]58' Streicher 21 Asterism 08 51.0 -80 10 E3 Globular 09 21.0 -77 17 NGC 2915 Galaxy 09 26.2 -76 38 NGC 3149 Galaxy 10 03.8 -80 25 NGC 3195 Planetary Nebula 10 09.5 -80 52 IC 2631 Reflection Nebula 11 09.8 -76 37 NGC 3620 Galaxy 11 16.1 -76 13 Sa 159 Dark Nebula 12 59.0 -77 10 Object Mag Size eta Chamaeleontis 5.4 8' Streicher 21 11.0 22' E3 11.3 5' NGC 2915 12.4 2.4' x 1.3' NGC 3149 12.8 2.0' x 1.9' NGC 3195 10.6 40" x 30" IC 2631 12.0 8.0' x 7.0' NGC 3620 12.7 2.8' x 1.1' Sa 159 -- 3[degrees] x 2[degrees] The constellation Chamaeleon is also home to a dark nebula which has been listed as Sa 156 in Sandqvist's Catalogue of
Dark Nebulae, published in 1977.
YOUR CHALLENGE: Using your lowest-power eyepiece, search the cloud's northwestern corner for a pair of starless "hollows." These are the
dark nebulae Barnard 92 and Barnard 93--thick dust clouds that block the light of stars lying behind them.