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M51 (NGC 5194 + NGC 5195) · Interacting Spiral Galaxy
Whirlpool Galaxy
The first galaxy in which a spiral structure was ever identified — sketched by William Parsons, the Third Earl of Rosse, through his 72-inch 'Leviathan of Parsonstown' in 1845. A textbook interacting pair caught mid-encounter with its dwarf companion NGC 5195.
M51 is one of the most photogenic galaxies in the northern sky: a grand-design spiral seen nearly face-on, with sharply defined arms wrapping around a bright nucleus and a smaller companion galaxy NGC 5195 dangling off the end of one arm.
The two galaxies are physically interacting. Tidal forces from the ongoing encounter have compressed gas in M51's spiral arms, triggering bursts of star formation visible in Hα as a string of glowing pink knots along the arm edges. Three confirmed supernovae have been observed in M51 in recent decades — SN 1994I, SN 2005cs, and SN 2011dh — making it a favourite target for transient hunters.
Its modest apparent size and high surface brightness make it ideal for medium-focal-length imaging. Long total integrations bring out the faint outer tidal streams that record the gravitational dance between the two galaxies; LRGB workflows tend to flatter its colour palette of dusty browns, blue arm regions, and pink star-forming knots.
// imaging sessions
session // 01
28.12.2025 OSC broadband — 200P + 183CA from Plau am See
- Gear
- Sky-Watcher Explorer 200P Newtonian · Sky-Watcher EQ5 Pro SynScan GoTo · ToupTek 183CA · TS-Optics 2" Newtonian coma corrector · Pegasus Astro Gemini EAF · 50/90 mm guide / finder scope · ToupTek 327C Mini guide camera
- Filters / frames
- None — bare OSC broadband
- Total integration
- ~2 h
- Frames
- ~120 min on target (02:16–04:31 local)
- Sensor
- gain 100
- Location
- Klebe, Plau am See, Mecklenburg · Bortle 3
- Software
- N.I.N.A. (Nighttime Imaging 'N' Astronomy) · Siril · GIMP · PHD2
Second half of the 28 Dec 2025 imaging marathon at Plau am See — picked M51 up after midnight once Canes Venatici cleared the trees. PHD2 guiding through the 50/90 + 327C, no filter in the optical path.
