Instrument

12.5" RCOS @  ~f/9 (2880 mm fl) at 0.64 arcsec/pixel. Shown at 1.06 and 1.28 arcsec/pixel.

Mount

Paramount ME

Camera

SBIG STL-11000 w/ FW8 filter wheel, AstroDon Gen-2 Filters

Acquisition Data

9/17/2014 to 9/12/2014 Chino Valley, AZ... with CCDAutoPilot, CCD Commander & CCDSoft, AOL guided.

Exposure

Software & Processing Notes

• CCDSoft, CCDStack, PixInsight, Photoshop CS6 and Noel Carboni's actions.

• No SDSS stars were available for color balancing, so a standard image-train color calibration was used, as determined by eXcalibrator v4.25, and then adjusted for altitude extinction.

• CCDBand-Aid to repair KAI-11000M vertical bars.

• CCDStack to calibrate, register, normalize, data reject, combine the sub exposures and create the RGB image.

• PixInsight processing includes gradient removal and the initial non-linear stretching with HistogramTransformation.

• PhotoShop for the final touch-up.

Comment

The cluster is shown rotated 143° counterclockwise.

Discovered 1745-46 by Philippe Loys de Chéseaux.

M71 is at a distance of about 13,000 light years from Earth and spans some 27 light years.
 

M71 was long thought (until the 1970's) to be a densely packed open cluster.  Modern photometric photometry detected a short horizontal branch in the H-R diagram of M71, which is characteristic of a globular cluster.  So today, M71 is designated as a very loosely concentrated globular cluster.

M71 is a wonderful example of how galactic extinction effects color. The cluster has a galactic latitude of only -4.6°. This means we view it through much dust and nebulae. This causes the color to shift towards the red, just like the Sun at sunset. Place your mouse over the image to see about how the cluster would look without the intervening dust.