Object Of The Week June 04, 2017: The dark clouds around M 11
Object Of The Week June 04, 2017: The dark clouds around M 11
B 106, 107, 108, 110, 111, 112, 113, 114, 115, 116, 117 and 118 and 318
Dark clouds, absorption nebulae
Constellation: Scutum
RA: Around 18h 51m
DEC: Around -06ยบ 15'
M 11 is a well known and beautiful open cluster at the tail of Aquila, the Eagle, though in fact it is in the constellation Scutum and lies at the eastern edge of the Scutum Star Cloud. This star cloud is visible south of the Great Rift that divides the Milky Way in two and here we are looking at the Sagittarius-Carina arm that is curving towards. Because it is curving inward, we are treated with a spectacular view along the edge of the arm. This manifests itself through the presence of open clusters and dark nebulae.
And dark clouds are the topic of this Object Of The Week, or rather Objects Of The Week. I found that in many cases binoculars and small telescopes are much better suited for observing dark clouds than large telescopes. The reasons are the much wider field of view that small telescopes can achieve on the one hand and the apparent size of dark clouds on the other hand. Despite that dark clouds can be hard to detect!
In order to see dark clouds a very dark sky is essential. We are looking for absence of light here and any source of light, including stars, can render a dark cloud invisible or at least less conspicuous. That's why in general I use low magnifications in combination with a wide band light pollution filter like the Lumicon Deep Sky Filter to block as much scattered light as possible whilst letting pass through star light as much as possible as well. This results in reduced glare from surrounding stars and a darker background sky, which increase the chances of spotting dark clouds in rich star fields.
Over the past 25 years I spent a week of observing under dark, southern France skies almost every year. I was there as well in August 2005, where I observed the dark clouds that are the topic of this OsOTW using my 6" home made Newtonian telescope using low magnifications and a Deep Sky Filter. My notes read
At 26x B 106 and 107 are visible as dark spots between the stars. B 110 is visible as well. B 113 is much clearer than these three.
Right next to M 11 lie 2 stars. West of that lies a large, dark complex which is split in two, particularly to the west. Just north of m=9 star SAO 142671 lies a dark spot. That's B 108. Two dark spots west of it and the large dark bar below belong to B 318. All of this is very clear, particularly the western parts.
B 112 lies due south of M 11. The dark cloud is visible really well. Actually it is made up of two parts. The northwestern part is largest, the southeastern part smallest. I got the impression that the dark cloud is confined by stars. The two part together fill about half of the field of view at 51x (so about a degree across).
B 114, 115, 116, 117 and 118 are visible as one dark cloud east of M 11. It runs about north south and is formed of 4 condensations that are connected together. I saw 117 and 118 as one dark condensation.
Of course these are not the only dark clouds in the summer Milky Way, nor in the constellation Scutum. Many of the dark clouds in this OsOTW (though not all) and several others are described in this article on the Sky and Telescope website, which also contains maps of this region.
As always,
"Give it a go and let us know!
Good luck and great viewing!"
