M11, also known as the Wild Duck Cluster, is a famous open cluster located in the constellation of Scutum. It's just beyond naked eye visibility but easily visible with binoculars and an outstanding telescope object. The brightest stars form a triangle that has been likened to a flock of flying ducks, hence the name Wild Duck Cluster. Of all know open clusters, M11 is one of the richest and most compact with about 2,900 members spread over a diameter of 25 light-years.
M11 was discovered by German astronomer Gottfried Kirch of the Berlin observatory in 1681. English clergyman William Derham is believed to have been the first person to resolve it into stars (around 1733), with Charles Messier adding it to his catalogue on May 30, 1764. The name the Wild Duck Cluster was provided by British Admiral William Smyth, who imagined the distinct V shape of the cluster as a flock of flying ducks.
The cluster is an easy target to find despite been located in the small and dim constellation of Scutum, whose brightest stars are of only 4th magnitude. The starting point on the way to the Wild Duck Cluster is to locate Altair (α Aql - mag. 0.8), the brightest star in Aquila and 12th brightest in the night sky. Altair forms the southern corner of the famous Summer triangle along with first magnitude stars, Vega in Lyra and Deneb in Cygnus.
To the southwest of Altair is mag. 3.4 star delta Aql (δ Aql). First imagine a line connecting Altair with δ Aql and then curve this line southwards for about the same distance again until you reach two 4th magnitude stars, λ Aql and 12 Aql. Located just over two degrees west of 12 Aql is the Wild Duck cluster.
M11 shines at mag. +6.3 and is an easy binocular object, appearing as a diffuse fuzzy ball with a noticeably brighter center. Its appearance is not unlike that of a loose globular cluster and is often mistake as one. A 100mm (4-inch) telescope will resolve M11 into a swarm of mainly sparkling white stars, with one bright standout member near the group's centre. When viewed through a larger 200mm (8-inch) scope, M11 is a spectacular sight with hundreds of stars visible including some yellow and red stars. Since it's compact, covering 14 arc minutes in diameter, magnification can be pushed up high to tease out more stars and details. In total, there are estimated to be at least 850 stars brighter than 17th magnitude.
The Wild Duck cluster is a tantalizing and fantastic rich open cluster when viewed through any type of optical instrument. It's best seen during the months of June, July, August and September. Since the cluster is one of the richest of its type, the density of stars in M11 has been the subject of discussion for decades. M11 contains some 80 stars or so per cubic parsec and an observer inside this group would see several hundred first magnitude stars in his night sky.
This is a truly wonderful open cluster and a must see on all observers lists.
M11 Data Table
|Name||Wild Duck Cluster|
|Object Type||Open cluster|
|RA (J2000)||18h 51m 06s|
|DEC (J2000)||-06d 16m 12s|
|Apparent Size (arc mins)||14 x 14|
|Age (years)||220 Million|
|Number of Stars||2,900|
|Other Name||Collinder 391|