M11
Wild Duck Cluster, NGC 6705
R.A.: 18h51m05.0s
Dec.: -06°16'12" (2000)
Magnitude: 6.10
Size: 32.0'
Trumpler Class I 2 r
With the bright skies of summer still affecting high northern latitudes it is worth picking a bright target
for this OOTW. Surprisingly not already covered by an OOTW the open cluster M11 in Scutum is one of
the most spectacular sights in a small telescope or binoculars. First discovered by Gottfried Kirsch at
the Berlin observatory in 1681 M11 was first resolved into stars by William Derham in the UK using an
8 foot focal length speculum in 1733, unfortunately he does not give the diameter of the mirror only
that he had to stop using it because it became too tarnished. Messier included it in his catalogue of
comet interlopers in 1764. The nickname of the Wild Duck cluster was given to it by Admiral Smyth
where he compares it to the shape of a flock of wild ducks in flight in his description in the Bedford
Catalogue, no doubt just before he took a shot at them! The brightest stars do indeed form a v shape.
Through a small telescope one bright star stands out amongst the others and the apparent dark shape
which delineates the cluster does indeed make it look like a V. The bright star, HD 174512, is also a
multiple star system. M 11 is one of the Messier objects that are visible to the naked eye. The cluster
is thought to be about 220 million years old and lies at a distance of perhaps 6200 light years from us,
although GAIA may push that out to 7200 lyrs. At this distance the core of the cluster is perhaps 20
light years across. This means that it is the most distant of the Messier open clusters that can be seen
with the naked eye. The cluster contains perhaps 2900 stars and will be expected to disperse due to
galactic tides over the next few million years or so. M 11 lies maybe 6.8 kpc from the galactic centre
and lies in the galactic plane, as perhaps one would expect for a young Pop I cluster.
m11pos.jpg
The brightest stars in it currently have a spectral type of B8, the more massive ones having already
evolved into red giants and gone. The cluster stars also show an enhancement of Alpha process elements
despite its youth, possibly due to the seeding of its birth cloud by a nearby Type II supernova. M11 is also
one of the most massive open clusters known with a possible mass lying between 2500 – 35000 Solar
masses. There is a very nice image of this cluster with the ESO 2.2m telescope at
https://www.eso.org/public/images/eso1430a/. M11 (or the core of it anyway) was also shot by Hubble at
https://www.spacetelescope.org/images/potw1912a/.
m11pan.jpg
PanSTARRS image courtesy of Aladin
As always give it a go and let us know.
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