M71, Globular Cluster in Sagitta

M71, NGC 6838, Magnitude 8.30, Size 6.1' x 6.1', Constellation: Sagitta

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: None.
• Acquisition: Meade Envisage. Quality = 30%.
• Guiding: None.
• Location: Pine Lake Observatory, Mobile, Alabama
• Date: 4 June 2005.
• Post Processing: Meade IP.
• Photoshop: Levels, unsharp mask, .jpg conversion.

When it comes to "loose" this is the king of the globs. This cluster, which looks like a barely visible star-knot in the city and suburbs, is impressive from dark skies only due to its marvelously rich field. Otherwise, it looks like a distant and unimpressive open/galactic cluster. The faint Open Cluster Harvard 20, which lies about 29 minutes to the east, doesn't look terribly different.

M71 is famous as the globular cluster that wasn't. For years, astronomers argued as to whether this was an open or globular star cluster. And they are still at it. While it's fairly well accepted that this is a very loose glob--it's HR diagram features a glob-like "horizontal branch"--it's status is still in doubt. Its color-magnitude diagram indicates that it could be either a younger globular or an older galactic.

This is one of the first DSI pictures I took. While there was little harm done to the image by the site's heavy light pollution, I'd like to do it over. I didn't realize that it's a good idea to leave the DSI's IR filter in place, and shot without it. Result? Muddy color and bloated stars.

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