Messier 101 The Pinwheel Galaxy

Messier 101, The Pinwheel Galaxy.Click here for an annotated version of this target.

M101 is a face-on, grand design spiral galaxy in Ursa Major. This is one of the nearest, most beautiful objects in the night sky. M101 is twice the size of the Milky Way at 170,000 light-years in diameter and is located 25 million light-years away.

Much like our own Milky Way galaxy, there are a lot of HII emission nebulae and star-forming regions. If you go to the annotated version of the image, you can see other NGC and PGC objects in the area.

In 1851, The Earle of Rosse, Willaim Parsons, discovered the spiral structure for the first time in the night sky. At the time, it was thought to be a nebula with star-forming regions, rather than a galaxy.

Parsons observed M101 using a 72-inch reflector telescope which had a focal length of 60ft. This was called “The Leviathan of Parsonstown”

In August 2011, we were able to observe a supernova in M101, this was the closest Supernova we have been able to observe in recent times.

The asymmetry in the spiral structure could be from the different speeds at which the galaxy is rotating. The inner parts of the galaxy are rotating faster than the outer edges, causing a compression of the galaxy. This phenomenon is called a density wave. The compression of gasses leads to pockets of star formation. The bright red regions here are the Hydrogen gas ionized by the young stars formed out of the gases.

Processing Info

I took almost 130 frames at 300 seconds. I was however plagued with some really weird focusing issues which caused me to throw away 50 frames. I took this over two nights at my local observing site. The third night, I was at a Bortle 2 site in Cherry Springs State Park under pristine skies.

I ended up with 80 usable frames. I calibrated it using 50 darks, flats, and dark flats.

The following processes were performed in PixInsight:

  • Channel Extraction
  • Linear Fit
  • Channel Combination
  • Dynamic Crop
  • Dynamic Background Extraction
  • Automatic Background Extraction
  • Background Neutralization
  • Photometric Color Calibration
  • EZ Decon
  • EZ Denoise
  • Histogram Transformation
  • LRGB Combination
  • Curves Transformation (X2 with a range mask. Inverted mask for the background and then non inverted for the target)
  • Color Saturation (X2 with a range mask. Inverted mask for the background and then non inverted for the target)
  • Curves Transformation (Using Luminance and Binary masks created using the GAME script)
  • SCNR (Removed Green)
  • EZ Star Reduction
  • Local Histogram Equalization (Performed with a range mask)
  • HDR Multiscale Transform

Once I found what I liked, I saved the files and went to Photoshop. I played around with the levels, vibrance, and saturation a bit.

The area of the sky in OrionHere you can see the area of the sky in Ursa Major imaged.

Acquisition Data

  • Telescope: Explore Scientific FCD100 Series 127mm f/7.5 Carbon Fiber Triplet ED APO Refractor Telescope
  • Camera: ZWO ASI2600MC Pro
  • Guiding: ZWO Off-Axis Guider with Helical Focuser
  • Guide Camera: ZWO ASI290MM Mini. Dithering every image at 1 pixel each time.
  • Mount: iOptron CEM60
  • Software: NINA for image acquisition. PixInsight used for stacking and editing. Imported to Photoshop for final touchup and watermarking.
  • Other Accessories: AstroZap Dew Heater, Astro-Tech 2″ Flattener, MoonLite CFL 2.5″ Focuser with a V3 Controller, PrimaLuceLab Eagle 4S
  • Filters: Optolong L-Pro (80 x 300s)
  • Exposure Time: 6 hours 40 minutes -20°C
  • Date: April 20, May 9 & May 15, 2021
  • Location: April 20 & May 9 at Voorhees State Park, NJ, May 15 at Cherry Springs State Park, PA
  • Bortle Dark-Sky Scale: 4 & 2
  • Mean SQM: 20.41
  • RA center: 14h 3′ 6″
  • DEC center: +54° 21′ 28″
  • Orientation:6.418 degrees
  • Field radius: 1.173 degrees
  • Magnitude: 7.86
  • Resolution: 3720 x 2330