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NGC 7023 (Caldwell 4) · Reflection Nebula
Iris Nebula
A blue reflection nebula in Cepheus illuminated by the young hot Herbig Ae/Be star HD 200775, embedded inside the larger dark molecular cloud LDN 1174. The contrast between the bright reflected starlight and the dust silhouettes of the surrounding cloud makes it one of the most photogenic reflection nebulae.
The Iris Nebula owes its name to the petal-like arrangement of bright lobes around the central illuminating star — HD 200775, a young Herbig Ae/Be star of around 4 solar masses that has not yet started fusing hydrogen on the main sequence. Its blue light reflects off the surrounding cloud of fine interstellar dust, giving NGC 7023 its characteristic cool azure colour.
The nebula sits inside a much larger dark cloud catalogued as LDN 1174 (Lynds Dark Nebula 1174). In deep imagery the bright reflection nebula is surrounded by intricate dust lanes and dark silhouettes — the dark cloud itself, foreground material that absorbs visible light from background stars. The contrast between the cool blue reflection and the warm tan-brown dust is a signature of the field.
For astrophotographers NGC 7023 is a broadband target — reflection nebulae dont emit, they scatter starlight, so narrowband filters would erase most of the signal. OSC or mono LRGB workflows both work well; the challenge is keeping the bright core from blowing out while still recovering the faint surrounding dust extending well beyond the bright lobes.
// imaging sessions
session // 01
19.10.2025 – 20.10.2025 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
- ~4 h 9 m (14,940 s)
- Frames
- drizzle stack, ~120 s subs
- Sensor
- gain 100
- Location
- Klebe, Plau am See, Mecklenburg · Bortle 3
- Software
- N.I.N.A. (Nighttime Imaging 'N' Astronomy) · Siril · GIMP · PHD2
Long overnight session at Plau am See — bare OSC behind the 200P at f/5. Drizzle-stacked at 14,940 s integration with GraXpert background extraction to pull the surrounding LDN 1174 dust silhouettes out from the gradient. PHD2 guiding through the 50/90 + 327C kept the round stars across the long session.
