M22, Globular Cluster in Sagittarius

M22, NGC 6656, Magnitude 5.10, Size 24.0' x 24.0', Constellation Sagittarius

Image Details:

• Scope: 1995 Celestron Ultima 8 OTA.
• Mount: Celestron AS-GT (goto CG5).
• Camera: Meade DSI Color.
• Configuration: f/3.3 focal reducer, no spacers, visual back/1.25" nosepiece.
• Effective Focal Length: 812mm, f/4 approximately.
• Exposure:  20 images @30 seconds.
• Filter: Meade IR blocking filter.
• Acquisition: Meade Envisage. Quality = 30%.
• Guiding: None.
• Location: Stargate Observatory, Fairhope, Alabama
• Date: 2 July 2005.
• Post Processing: Meade IP.
• Photoshop: Levels, unsharp mask, color balancing, .jpg conversion, star size reduction, color noise reduction.

Comments: M22 is one of the most wondrous objects in the sky for visual observers. When  it comes to globular clusters, it's outclassed only by Omega Centauri and (possibly) 47 Tucanae. For Northern Hemisphere observers at 30 degrees latitude and below, M22 easily leaves M13 in the dust. It is richer and looser. Almost any scope can resolve some of its stars (which are at magnitude 11 and dimmer); I've had good looks at it with my Short Tube 80 refractor from dark sites.

M22's "close" distance of around 10,000 light years is the explanation for its majesty. Otherwise, it's fairly average as globs go, with a diameter of about 70 light years and a luminosity equivalent to 210,000 suns.

When you're getting started with CCDing, globular clusters are the objects to begin with. They are easy to focus on, reasonably bright, and forgiving of processing "mistakes."  I submitted this one to Meade's DSI gallery, but no dice, despite the fact that it looked as good or better than what was on their website at the time in the days before the DSI Pro and DSI II.  Maybe they didn't like the fact that I shot it with a C8? Main thing I'd like to do over on M22? Get the focal length down. This is a big sucker and needs more field. I think the focus could be a little better, too. Next summer...

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