Sh2-125 — Cocoon Nebula
HII Region in Cygnus
About
IC 5146, the Cocoon Nebula, a star-forming cloud in Cygnus that is partly glowing hydrogen, partly reflected starlight and partly dark dust. Sources give its distance as roughly 2,500 to 4,000 light-years. A dark lane, Barnard 168, trails westward from it like a tail.
Imaging tips
- At 2,420–4,040 mm on APS-C the nebula fills a third to half of the frame; one imager shot at 430 mm to include the dust tail, and AstroBackyard says many would call that too short.
- It mixes emission, reflection and dark nebulosity: broadband colour works, and one imager added Hα to an LRGB set.
- One imager's 2017 DSLR image used only one hour; another reached 52 hours in total for a single image.
- B168 sits right beside it, so its dust is in the same field; the wider tail needs a wider lens.
- Best in August and September; it passes almost overhead, about 87° altitude from 50°N.
Facts
- Size
- 12′
- Magnitude
- —
- Coordinates
- RA 21h 53.5m, Dec +47° 15′
- Framing, APS-C
- 2020–3370 mm
- Framing, full frame
- 3090–5160 mm
- Best months
- Aug, Sep
- Peak altitude
- 87° from 50°N, 78° from 35°N
Nearby
- B168 · 1.9′ away