M 22 (NGC 6656, GCL 99) Globular Cluster in Sagittarius

Located at: RA 18 hours 36 minutes 24 seconds, Dec -23 degrees 54 minutes 12 seconds

Size: 32' Magnitude: 5.2 Class: 7

North is up

West to the right

Telescope:

14.5" f5 Newtonian reflector

Camera:

 ST-8XME, self-guided, binned 1x1, temp -15c, camera control MaxIm DL 4.56

Image:

Lumicon Red filter, 300 minutes (60 x 5 minute {300 seconds} subs), 08/17/18/19/2015; seeing 2.6-4.6 FWHM per CCDStack

Processing:

CCDStack 2.90.5589.16047, Photoshop CS5.1

Location:

 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)

Notes: This magnificent southern globular cluster has a cataloged size that is larger than my vertical field of view (about 17 arc minutes). M 22's outer stars merge into the dense Milky Way background in this image. See here for a 14.5" f5 Newtonian film image on hypered Kodak Tech Pan 2415 film. See the 8" ccd image.

From the NGC / IC Project:

Contemporary Visual Observation(s) for NGC 6656
NGC 6656 = M22 = E523-SC4
18 36 24.1 -23 54 12
V = 5.2;  Size 24.0

17.5" (8/4/94): at 220x appears 10' diameter although outliers may significantly 
increase the total diameter.  The very bright core is irregularly round and 
3.5'-4' diameter but not concentrated to the center.  M22 is extensively 
resolved to the center and there is no distinct nucleus.  At the NE edge of the 
core is rich small clump with 8-10 stars that collectively stands out well and 
an easy bright pair is at the SE edge of the core.  The very irregular halo 
appears more extensive on the NE side and appears elongated SW-NE.  Dark lanes 
appear to intrude into the cluster and involve the surrounding region though 
this may be an optical effect.  This is the third brightest globular in 
integrated magnitude (V  = 5.2) and a difficult naked-eye object in a dark sky 
(fairly easy from Australia, but not as obvious as I would have expected).

8": very bright, very large, extremely rich.  A few hundred mag 11-13 stars are 
resolved and appears highly resolved down to the core.  A bright clump is 
visible in the NE section of the core.  Varying magnitudes to the cluster 
members.  M22 is the second best globular for viewing from Northern California 
(next to M13, although has brighter members).

- by Steve Gottlieb