The final result is the combination of 4 images at 120 seconds in Luminance for a total of 8 minutes exposition with a Planewave CDK 24” in Sierra Remote Observatory at Auberry California.
I used IRIS and Fitswork for registration, stacking and editing, Lightroom CC for visual enhancement of the LRGB image, Astrometrica for astrometric calibration, APT for photometry analysis and other tools like Aladin, TOPCAT, CDS Portal website for subsequent analysis.
For the color image I used the R (POSSII F) and B (POSSII J) channel photos from The Digitized Sky Survey 2 using the SkyView server and synthetized the G channel with IRIS.
NGC 6946 is a medium-sized, face-on spiral galaxy about 22 million light years away from Earth. In the past century, eight supernovas have been observed to explode in the arms of this galaxy. Chandra observations (purple) have, in fact, revealed three of the oldest supernovas ever detected in X-rays, giving more credence to its nickname of the “Fireworks Galaxy.”
NASA
The error over 2 mag is due to the fact that many small stars are close to brighter sources and so the automatic calculation failed to analyze these sources.
