1.About the M51:
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs (23.5 million light-years) away and 23.58 kiloparsecs (76,900 ly) in diameter.

The galaxy and its companion, NGC 5195, are easily observed by amateur astronomers, and the two galaxies may be seen with binoculars.The Whirlpool Galaxy has been extensively observed by professional astronomers, who study it and its pair with NGC 5195 to understand galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions. Its pair with NGC 5195 is among the most famous and relatively close interacting systems, and thus is a favorite subject of galaxy interaction models.  (Write up by Wiki)

2.Story of the Data
Raw datra was collected by Me and Barry, from March 3rd to April 5th.

2-A Me and Barry
The rainy season of Daocheng usually occupies April to September, covering almost half of a year, and may compromise our plan during the galaxies season. Me and Barry knew each other on DGO, the DaoCheng Glacier Observatory,  while his 10'' WORC were in roof A and my WORC12 was set in roof B. So, we are happy to collab with each other and share data, so as to take as much expoure as we can in these few month for our beloved tiny galaxies. 

2-B Integartion
The total integation is about 78 hrs,  consists of the following data taken by Barry and me:

1. Lum 137 x 600s = 22h50m
2. Red 136 x 300s = 11h20m
3. Green 147 x 300s = 12h15m
4. Blue 144 x 300s = 12h
5. NB Ha 118x 600s= 19h40m

3.Equipment
Both me and Barry use RC telescope of William Optics, the angle of stars spike are excatlly the same (guess all the WORC share a same angle?)
     3-A: Barry's Set

1. Telescope: William Optics 10" f/8 Ritchey-Chretien Truss Tube
2. Camera: ZWO ASI2600MM-Pro
3. Mount: Sky-watcher EQ8r-Pro
4. Filters: Antlia Dark Series LRGB, 3nm Ha

     3-B: John's Set

1. Telescope: William Optics 12" f/8 Ritchey-Chretien Truss Tube
2. Camera: ZWO ASI6200MM-Pro
3. Mount: iOptron CEM120EC
4. Filters: Antlia V Pro LRGB, 4.5nm Ha
5. Flattener: William Optics Dr. Flat Master for GSO RC (12"-16") (Flat-RC)

4. Process
During the linear processing stage, everything was pretty and fine. I just follow my old way, DyCrop, DBE, BlurX and SPCC.

However, problems came when I moved on to non-linear stage. The galaxy is way too bright than the dust or tidal stream around it, which made me really hard to keep a balance between them. Moreover, HDR process did not work well when it comes to such a bright galaxy and a dark dust like this. I tried seveal times, and finally achieved some decent result with masked HT and double HDR.
Tidal stream was enhanced using LocalHistorgramEqualiaztion process, with larger ridus parameter, but I personally did not like that very much and throw them later.

The Ha data was added during the non-linear stage, with PS. We wanted to capture the amazing Ha cliff found before. But our Ha data was way to less, only about 20 hrs. The weather of DGO became bad in April so we decided to pause here and wait for next year.

5.Location:
Daocheng Glacier Observatory, Sichuan,China.


Special thanks to:  Grapeot, who kindly shared his briliant method of adding stretched Ha data to LRGB using Photoshop. He has uploaded tutorial on YouTube and Bilibili. 

Hope that you guys will enjoy this image!