Casitas de Gila, Gila, New Mexico, March 27, 2023

During my Spring trip to a dark sky site in New Mexico, M12 was the last target for imaging for one night.  I was able to obtain about 2 ½ hours of data before morning. So, the result is not up to par.

Description:

Messier 12 (NGC 6218) is a globular cluster in the constellation of Ophiuchus.  It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a "nebula without stars".  The cluster is about 16,400 light years from Earth and has a spatial diameter of about 75 light years.  The brightest stars of M12 are of 12th magnitude. M10 and M12 are only a few thousand light-years away from each other.  It is rather loosely packed for a globular and was once thought to be a tightly concentrated open cluster.  Thirteen variable stars have been recorded in this cluster.  M12 is approaching us at a velocity of 16 km/s.  Like the other ~250 globular clusters orbiting the Milky Way, M12 is composed of very old stars, perhaps 10 to 12 billion years,  as indicated by their poor metallicity. (Wikipedia)

Imaging and Processing:

Time was running out for imaging, especially with the moon moving towards first quarter.  So, only limited data were collected for this globular cluster.  Furthermore, the new Celestron dew heater ring for my SCT was running somewhat aggressively as the dewpoint neared the ambient temperature.  I did dial the Pegasus Astro Ultimate Powerbox 2 controller setting, but not enough to eliminate a serious optical issue.  The excess heating of and around the corrector plate created two stubby diffraction spikes on brighter stars, making them look like blurry Saturns.  This unwitting experiment confirmed a thread on Cloudy Nights describing the problem.  While I tried to clone stamp my way to a better image, there were too many stars with these annoying defects to be properly repaired.

Imaging details:

Celestron 9.25" Edge HD SCT (FL = 2350mm at f/10)
Celestron Off-axis Guider with ZWO ASI 174 mini guide camera
Losmandy G11 mount with Gemini 2 controller
ZWO ASI 2600MM Pro cooled monochrome camera (-10C)
36mm Chroma filters: Red, Green, Blue

Software: Sequence Generator Pro, PHD2 guiding, Losmandy Gemini 2 ASCOM driver,
SharpCap Pro with QHY Polemaster camera for polar alignment, 
PixInsight and Photoshop 2023

Red       2 min x 26 subframes (52 min), Gain 100, Offset 32, 1x1 binning
Green    2 min x 26 subframes (52 min), Gain 100, Offset 32, 1x1 binning
Blue      2 min x 26 subframes (52 min), Gain 100, Offset 32, 1x1 binning

Total integration time: 2.6 hours