M11 (NGC 6705)

1. The history
2. To find M11
3. To observe M11
4. The stars of M11

M11, also called "the Wild Duck cluster", was discovered by the German astronomer Gottfried Kirch of the Berlin observatory; he described it as "a small, obscure spot with a star shining through and rendering it more luminous"; in 1715 Halley included it in his list of "nebulous stars", but Derham was the first to resolve M11 into stars (1732): "It is not a nebula but a cluster of stars somewhat like that which is in the Milky Way"; Le Gentil, in 1749, described it as "a prodigious cluster of very small stars, forming a large, white cloud......"
Messier listed M11 in May 1764.
William Herschel thought M11 just visible to the naked eye.

M11 lies on the northern edge of the Scutum Stellar Cloud, about 2° a SSE from b Scuti.

"A very beautiful and impressive, compact cluster" (Kenneth Glyn Jones); "One of the richest and most compact of the galactic clusters." (Burnham). It can resemble, in binoculars, a globular cluster, but increasing magnification the stars draw apart, revealing a very dense but open cluster.

About 1° NW from M11 is the variable star R Scuti. an RV Tauri type, semipulsating variable of period 140 to 146 days with a range of 4.8 to 6.0 mag.

M11 contains an estimated 2900 stars, about 500 of which are brighter than mag 14. An observer at the center of M11 would see several hundred first magnitude stars.

The angular size is given with discordant values; Barnard gives 35', the Sky Catalog 2000.0 estimates 14'.

The age of the Wild Duck cluster has been estimated to amount 220 million years, as its brightest and hottest main sequence stars are of spectral type B8 (according to the Sky Atlas 2000), but also double that value (Burnham gives 500 million years). The higher value is supported by the fact that this cluster also contains many yellow and red giants of absolute magnitude around -1.0.

It is receding at 22 km/sec.