M33 is the third largest galaxy in our Local Group of galaxies which includes M31 (the Andromeda Galaxy), and our own Milky Way Galaxy. Visually, the galaxy is quite large - about 70' x 40'. This makes the galaxy about 3 times larger than the Full Moon. However, unlike the Full Moon, M33 has a very low surface brightness, so it is quite challenging to see as well as to photograph.

The Triangulum Galaxy has many HII (Hydrogen Gas) regions. In this picture, you can see these HII regions as the magenta colored areas. Similar to the Orion Nebula and Lagoon Nebula, these regions are areas of star formation. Many of these HII regions are identified in the annotated version of this image along with over 20 background galaxies.

In this image, North is to the Left. This image is cropped to 52% of the original full frame.

Exposure Details
Lens	Nikon 600mm f/4 ED IF
Focal Length	600mm
Focal Ratio	f/6
Mount	Schaefer GEM - 7 1/2 Byers gear
Guiding	William Optics 50mm guide scope, Lodestar autoguider, PHD Guiding
Camera	Hutech modified Canon 6D
Exposure	174 RGB subexposures of 300 sec at ISO 1600 (14 1/2 hrs) plus 154 Ha subs of 600 sec at ISO 1600 (25 2/3 hrs) - 40+ hours of total exposure
Calibration	30 darks, 30 flats, 30 bias
Date	10/9, 10/10, 10/11, 10/20, 10/30, and 10/31/2015
Temperature	67F on 10/9, 60F on 10/10 and 10/11, 48F on 10/20, 56F on 10/30 and 10/31
SQM Reading	21.35 (Bortle 4) on 10/9, 10/10, 10/11, 21.20 (Bortle 4) on 10/20, 21.15 (Bortle 4) on 10/30 and 10/31 (brighter when Moon was up)
Seeing	3 of 5 on 10/9, 10/11, and 10/30; 4 of 5 on 10/10, 10/20 and 10/31
Location	Pine Mountain Club, California
Software Used	Images Plus 5.75 for camera control. Images Plus 6.0.5 for calibration, stacking, ArcSinH stretching, star size reduction, smoothing and noise reduction, vertical band suppression, adaptive Lucy-Richardson restoration, color channel splitting and recombination. Photoshop CS5 used for levels and curves, screen mask invert, high pass filter, lab color, saturation adjustments, selective color, and match color. Gradient Xterminator for gradient removal. Carboni Tools for additional noise reduction and smoothing. HLVG for additional color correction. Registar 64 for subexposure alignment and color channel alignment. Pixinsight 1.8 for multiscale median transformation and morphological transformation.
Notes	This is the third time I've imaged this beautiful galaxy. The good news is that I feel it is improving with each new version, so at least my efforts aren't for naught! In my second try at M33, I had added Ha data to fill in the colorful HII regions. While I did the same thing with this version, I have learned better how to control this process, so I ended up with a very good representation of these star forming regions. All in all, I'm very happy with how this image looks.