§ Deep Sky · Emission Nebula · 2025.11
IC 1805 — Heart Nebula
A massive emission nebula in Cassiopeia spanning over 200 light-years, its distinctive cardiac silhouette carved by radiation pressure from the young open cluster OCl 352 at its core.
The Heart Nebula is approachable as a beginner target in the sense that it is large, bright, and unmistakable — but imaging it well is another matter entirely. A single broadband exposure shows almost nothing: the Hα emission that defines IC 1805 is buried under the noise floor of any camera without filtration. Narrowband imaging exists precisely for targets like this.
I chose the Hubble Palette (SHO) for this image — mapping Hα to green, OIII to blue, and SII to red. The results look nothing like what the eye would see, but they reveal ionization structures and gas dynamics that broadband simply cannot show. The hollow cavity at the center of the nebula is sculpted by intense UV radiation from the hot young stars of OCl 352; the "wall" of the surrounding nebula glows in Hα as the shock front propagates outward into the surrounding molecular cloud.
The SII signal in this nebula is notably weak — much weaker than the dominant Hα — which required the longest per-filter integration of the three channels to pull out of the noise floor. The final 22 hours of data were gathered across six nights throughout November 2025, working around the new moon window to keep the sky background as dark as possible.
[Replace this paragraph with your personal session notes — seeing conditions, any nights you had to throw out, how you handled the SII data, and what the final processing workflow looked like.]