Open Cluster (NGC 7092), type 'e', in Cygnus

RA 21:32.2 (h:m); DEC +48:26 (deg:m); Distance 825 (ly); Visual Brightness 4.6 (mag); Apparent Dimension 32.0 (arc min).
M39 is a very large but very loose open cluster, situated some 9 degrees east and a bit north of Deneb (Alpha Cygni). Its distance is only about 800 light years, and it is of intermediate age (estimates between 230 and 300 million years). 30 stars are proven members and contained in a volume of about 7 light years diameter.

This cluster is best observed with lowest powers because of its considerable angular size of 32 arc minutes, more than the Moon. Under good conditions, it can just be glimpsed with the unaided eye. It is well seen in opera glasses and smaller binoculars as a nebulous object, resolved in a 7x50, great at small powers, where its shape stands out: An equilateral triangle with a bright star at each corner, the southerly side aligned about East-West: a 9th mag star at its Northern corner, and one of 7th mag each at the SE and SW corners. About 25 fainter stars within. Many of its stars are grouped in pairs. The cluster is impressive and despites its looseness, well defined in and detached from a rich Milky Way star field. At higher magnifications it fills many fields and gets less impressive.

Source and more: SEDS

August 13, 2008 21:31 - 21:47 UT.
Imaging: William Optics Zenithstar 80 ED II APO at f/6.8 [focal length 545 mm], ATK16IC camera, Astronomik LRGB filters.
Exposures: L: 5x60s [1x1]; RGB: 5x30s [2x2], unguided.

September 27, 2006 21:42 - 22:02 UT.
Imaged with Bresser Skylux [a.k.a. Lidl scope] 70mm f/10 with 0.6 Mogg focal reducer operating at f/6.2 and Baader Infra Red Blocking Filter.
The Skylux scope was piggybacked on my LX200.
Camera: Vesta Pro SC3a bw RAW webcam; 40 x 30 seconds exposures, autoguided.

October 6, 2004 20:54 - 21:07 UT.
Imaging and postprocessing as per my DSO imaging tutorial.

October 6, 2002 20:40 UT.