Object of the Week, June 25 2017: Barnard 72, the Snake Nebula

Object of the Week, June 25 2017: Barnard 72, the Snake Nebula

Dark Dust Clouds in Ophiuchus
RA: 17h 23' 30"
Dec: -23 38" 00"

Barnard 72, The Snake Nebula

Almost everybody is aware of the magnificent Horsehead Nebula in Orion, arguably the best known animal - like dark nebula on the heavens, but few are aware (and significantly fewer have actually seen)another animal – like dark nebula, almost diametrically opposite in heavens, the Snake Nebula (Barnard 72).

As the official name suggests, B72 is the 72nd dark nebula in the list of dark nebulae detected by E.E. Barnard on photographic plates he took in the late 1800s and early 1900s at the University of Chicago. Barnard 72 is an S-shaped cloud of dust, and as projected in front of thousands of faint Milky Way stars in Ophiuchus, it is quite remarkably snake-like in photographs of the region. But detecting it visually is another story.


As someone who actually likes snakes, I was always fascinated by this beautiful dark cloud. But it took many years before I was able to detect it with certainty. The main problem is that although in photographs this cloud is seen against a background of multitudes of stars, using a telescope these stars merge into a very faint glow barely brighter than the background sky. Locating the field is a breeze, especially this summer as Saturn resides less than two degrees to the northeast. But once you detect the correct field, then it takes a lot of effort under clean dark skies before some parts of the Snake Nebula materialize in the eyepiece.

Attachment 2594
Photo of the Snake Nebula by the author, taken using a Takahashi FSQ106N and a DSLR from his backyard observatory


After several attempts during recent years with uncertain results, I was finally able to nail it down this June using my 6 inch achromatic refractor and my Ethos 21 eyepiece. With this setup I really detected the middle “fat” part of the body, which is the darkest part of the nebula. Unlike the Horsehead, which is silhouetted against bright nebulosity that responds to filters, the Snake is projected against stars, making filters useless. But there was a way to increase the brightness of the background stats, and this was to increase the magnification, albeit at the expense of precious exit-pupil. In my 6-inch, the best view was with my 13mm Ethos which brightened the background sufficiently without giving me an exit pupil too small to detect the subtle dark nebula. Using the 13mm I was able to detect what looks like the “head” of the snake (albeit it was very hard to see), the easy middle part, and part of the thin “tail” of the snake.

Attachment 2595
Drawing of the Snake through a 6" refractor

Unfortunately I did not get around trying to detect the Snake with my 18” dob, but I had a chance to observe it through Nicoscy beautiful 5” APO refractor with similar results. Now that I have managed to detect the main body parts of the snake, I hope I will be soon able to trace the whole body. Has anyone on this forum managed to detect the whole body of the Snake? Who has seen parts of it? I hope to see lots of observations, though the fact that I could trace very few visual observations on the web makes me a bit pessimistic.

So, next new moon, when you get out under dark and steady skies, seek the Snake,

GIVE IT A GO, AND LET US KNOW!

We took a look at the Snake form Hakos, Namibia in 2012. I was surprised not to have seen it with my 4" Newtonian. I expected it to be much easier. But in the 16" Dobsonian it was a beautiful field! High contrast dark nebulae floating in front of the stars, almost like in 3D. It was very much like the photos. Unforunately no drawing. I'd probably need a couple of months to draw that sea of stars.
Besides this I've never seen the Snake from Central Europe.

Great Object Rolando! I do not fear the SNAKE :D

For middle Europe it is always tough to detect the snake as Peter already mentioned. From an High Alps observing place (47°N) with good to very good transparency it mostly is no problem and test object for transparency.

From Namibia it is of course a beauty with all its structures like star knots, loose star fields and the Barnard holes with their different opacities. I tried to plot the star field in a sketch but it is difficult to sketch like the eye could perceive it.

14.5", 83x, NELM 7m0+ (Hakos/Namibia)
Attachment 2599

As others have noted, the Snake is surprisingly low contrast (visually) unless conditions are excellent or from southern latitudes. This observation was from northern California --

18" (6/7/08): surprisingly large, low contrast dark nebula at 100x. The Snake Nebula is most evident and easiest to trace along the southern portion, forming a large U-shaped loop roughly 10'x6' in size, with the base of the "U" extended ~E-W. The unresolved glow of the rich Milky Way forms a glowing background in the surrounding field and highlights the edges of the "U" shape. The thinner western reverse loop was difficult to trace.

By the way, as far as I can tell, Barnard didn't call the shape a "Snake". His notes read "This is a striking object. It is a thin, curved black marking, the exact form of the letter "S" or the figure "5", as the imagination or point of view may dictate. The southeast branch runs easy for some distance passing close south of a mag 9.2 star. Its average thickness is 2'-3'. The position in the catalogue is for the southern part of the figure."

Heber Curtis called it "S-shaped "hole" or dark nebula. This remarkable object is about 22' long; would show better on plates taken with instruments of shorter focus. In a dense region; the object itself is amost perfectly blank."

So, I'm curious if anyone knows the earliest reference to the "Snake Nebula" nickname?

I have one observation of B72 from 1999 with my old 20 inch f/5:

"Wow! Looks just like I hoped, a little larger perhaps. Rather subtle contrast but its connection to the Pipe dark nebula is apparent. B68, 69 and 70 line up just to the west of the Snake with B68 the most prominent. 83x."

No idea when and who coined its nickname, but time to have another look at this one too.