Dark Matters

Jack Kramer

When Edward Emerson Barnard turned the instruments of Yerkes Observatory toward star-filled areas of the sky, he took note of a strange phenomenon. There were dark spots of various sizes and shapes. His predecessors going back to William Herschel had concluded that these were simply areas where there weren't any stars -- "holes in the sky". But Barnard decided that the opposite was true. He believed that instead of being empty areas, these were, in fact, concentrations of matter that blocked our view of what lay beyond. Knowledge gained in the ensuing years has proved that he was correct.

The CCD image below shows an area of the sky in southern Ophiuchus centered on "The Snake" -- one of the more recognizable dark nebulae. Each of the prominent dark nebulae is designated with a Barnard number. "The Snake" is B72, while the nebula immediately to the left is B77 and the areas above are B261 and B262.

These dark nebulae (sometimes called "coal sacks") are visible in amateur-sized instruments. The important thing is to use a telescope with low power and a wide field. The most prominent of these objects may be detectable even in binoculars. The best hunting is in a part of the sky with an ample supply of background stars, such as the Milky Way. Very seldom do these objects jump right out at you, but in a dark sky you'll note areas that have fewer stars, and it's helpful if the dark nebula has a definite shape. Note the emphasis on observing from an area with dark skies. As with everything else, light pollution seriously compromises the view of dark nebulae. In my 10" scope I could not detect the entire extent of "The Snake" -- just the most sharply-curved section, which also happens to be the darkest portion.

If you set out to find some dark nebulae, one problem you'll encounter is that the majority of star atlases don't show any of these objects. The Uranometria 2000 is about the only popular star atlas that identifies a large number of them. A large-scale photograph of the Milky Way shows many such objects, but seldom are the photos captioned so you can tell exactly which Barnard object is which. For locating purposes in the image here, the brightest star at the bottom is 44b in Ophiuchus.

Research has shown that many galaxies are full of this dusty primordial matter. Even our own telescopes will show absorption features -- dust -- in some of the other bright galaxies. Considering that this dust is often the progenitor of new stars yet to be formed, we are indeed seeing the real stardust, despite what songwriters and romantics may say!

Some Dark Nebulae in Ophiuchus and Sagittarius from the Saguaro Database


ObjectOther NamesRADecU2000TirionSizeClass
B 42,44-7 16 38.0-24 0633622600'6 Ir
Contains B51 and B238,Narrow dark lanes extending following Rho OPH
B 46LDN 177516 57.2-22 443372212' 6 Ir G
30' north of 24 OPH
B 57LDN 11 17 08.3-22 5033722 5'6 E G
In patchy region following B44
B 59,65-7LDN 177317 21.0-27 0033822 300'6 Ir
2 deg south of Theta OPH, Stem of Pipe nebula
B 60,246LDN 17 17 11.8-22 273372230'X20' 3
In patchy region following B44
B 6117 15.2 -20 213372210'X4' 6 Ir
1 deg south preceding B63
B 62LDN 10017 16.2-20 533372225'X15'6 Ir
30' south preceding B63
B 63LDN 99 17 16.0-21 2333722100'3 Ir G
3 deg north-north foll Theta OPH, with a globule at preceding end
B 64LDN 173 17 17.2-18 323371520'6 Co
30' preceding globular cluster M9 -Large, very dark, triangular, only 3 stars involved
B 67aLDN 102 17 22.5-21 53338 22 16'6 Ir G
3 deg north of Theta OPH
B 68LDN 5717 22.6 -23 4433822 4' 6 K G
20' south preceding B72
B 69LDN 55 17 22.9-23 53338224'6 Ir
15' south following B68
B 70LDN 54 17 23.5-23 58338224'4 C?
20' south following B68
B 72LDN 6617 23.5 -23 383382230'6 S G
The Snake,1.5 deg nnf Theta OPH - 13''-pL,p Dark, thin winding Dneb
B 74 17 25.2-24 123382215'X10'5 Ir
15' preceding 44 Oph
B 75,261-2 17 25.3-22 2833822110'5 Ir
Two arcs 1 deg north following B72
B 77,269LDN 69 17 28.0-23 2233822100'3 Ir
Faint extension of bowl of Pipe nebula
B 78LDN 42 17 33.0-26 0033822200' 6 Ir
2.5 deg south following Theta OPH, Bowl of Pipe nebula
B 79,276LDN 21917 39.5-19 473381550'X30'6 Ir
B79 is narrow, straight north preceding extension
B244LDN 173617 10.1-28 243762220'X30'5 Ir
Lies south of tip of Pipe nebula
B256LDN 1749 17 12.2-28 513762250'X10'5 Ir
1.5 deg south of stem of Pipe nebula, Curved
B259LDN 177 17 22.0-19 19338 15 30'4 Ir
50' south following globular cluster M9 - L, horn-shaped, 4* involved
B268,270LDN 178 17 32.0 -20 3233822120'5 Ir
Uncataloged 16 47.8-12 05291 15 150'6 Ir
Narrow north-south lane


ObjectOther NamesRADecU2000TirionSizeClass
B 83aLDN 233 17 45.3-20 0033822 4'6 E? G
On star cloud 1.7 deg north, 30' following 58 OPH
B 84LDN 235 17 46.5-20 113382230'X15'6 Ir
1.5 deg north, 40' following 58 Oph,B83a nearby
B 84a LDN 302 17 57.5-17 4033915 16'5 C
1.5 deg north of cluster M23, with faint extension to south
B 8518 02.6 -23 0233922
Dark regions in Trifid nebula - very distinct dark nebula
B 86LDN 93 18 02.7-27 50339224'5 Ir G
On SGR star cloud preceding cluster NGC 6520, Ink Spot Nebula
B 87LDN 1771 18 04.3-32 30377 22 12'4 C G
Parrot's Head, 4.5 deg south of cluster NGC 6520
B 88-9,286 18 03.8 -24 2333922
Dark regions in Lagoon nebula
B 90LDN 108 18 10.2-28 19377 22 10'6 Ir G
1.5 deg following,20' south of cluster NGC 6520
B 91LDN 227 18 10.0-23 39339 22 5'X2'5 K
Adjacent to bright nebulae IC 1274-5
B 92LDN 323 18 15.5-18 113391512'X6'6 E G
On NW edge of Small Sagittarius Star Cloud, very prominent
B 93LDN 327 18 16.9-18 0433915 12'X2'4 Co G
30' following B92
B303LDN 210 18 09.2-24 07 339221' 5 S
In bright nebula IC 4685

Published in the July 1997 issue of the NightTimes