Sharpless 119 (Sh2-119), also known as the Clamshell Nebula, is a large emission nebula located in the constellation Cygnus, roughly 2,200 light-years from Earth . It lies only a few degrees east of the North America and Pelican Nebulae, making it part of the same expansive star-forming region of the Cygnus molecular complex .
Physical and Visual Characteristics
SH2-119 spans about 2.5 light-years across and presents a distinctive clamshell-like structure, which gives it its nickname . The nebula’s structure is illuminated primarily by the bright blue star 68 Cygni (magnitude 5), which provides ionization for the hydrogen gas in the region, resulting in strong hydrogen-alpha emission . Dark nebula filaments, containing mostly hydrogen and helium with a small percentage of dust, thread through the emission regions and create intricate contrasts between glowing gas and obscuring dust .
Imaging and Observation Notes
SH2-119 is a relatively faint target compared to nearby SH2-117 (the North America Nebula), meaning long hydrogen-alpha exposures are essential for revealing its structure . The nebula responds strongly in Hα but weakly to OIII, making it more suitable for Hα-RGB imaging rather than SHO narrowband combinations . Widefield telescopes (with over a 3° field of view) capture its full expanse best, while higher-resolution systems can focus on its darker dust lanes and internal detail .
Imagers often describe the field as richly populated with stars, with the combination of emission, reflection, and obscuring dust offering both scientific and aesthetic appeal .
Context within Cygnus
The Cygnus region housing SH2-119 is one of the richest areas of the Milky Way in terms of emission nebulae and star-forming regions. Together with SH2-117 (North America Nebula) and Sh2-120, SH2-119 contributes to one of the most active HII regions visible from Earth during the northern summer months .
For astrophotographers using systems such as Takahashi refractors or fast astrographs (f/3–f/5), extended integration times—often exceeding 10 hours—are recommended for bringing out its fine filaments and gradual transitions in Ha emission .
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