Cave Nebula (in Ha)

I really like colorful astro images, but every now and then an object lends itself to just plain 'ol mono, albeit in this case mono at a single light frequency - that of Hydrogen Alpha, or Ha.  Normally, I would shoot two or three NB images (Ha, Oiii and Sii) and add in the broadband colors of R, G and B. On December 10 and 11 I took a small number of RGB and a lot of Ha, 40 subs each 10 minutes long. The RGB images just weren't good enough to use - this object needed at least 2 hours of each and I had only about 15 minutes of each. So I decided to process this DSO (Deep Space Object) in the Ha band only.

So here is the Cave Nebula, or Sh2-155.

Sh2-155 (Cave Nebula) in Ha
December 10, 11, 2018    GT102 at f/5.5    ASI1600mm Pro
40x600sec (6.7 hrs integration)

Sh2-155 (also designated Sharpless 155 or S155) is a diffuse nebula in the constellation Cepheus, within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the Cave Nebula, which was coined for this object by Patrick Moore, presumably derived from photographic images showing a curved arc of emission nebulosity corresponding to a cave mouth. Although Sh2-155 is relatively faint for amateur observation, some of its structure may be seen visually through a moderately sized telescope under dark skies. Sh2-155 lies at the edge of the Cepheus B cloud (part of the Cepheus molecular cloud), and is ionized by young stars from the Cep OB3 association. It has been suggested that radiation from the hot O-type star HD 217086 is compressing the region, triggering the formation of a new generation of stars. A study of the region's young stellar objects by the Chandra X-ray Observatory and Spitzer Space Telescope shows a progression of stellar ages in front of the cloud, supporting the hypothesis of triggered star-formation. (Wikipedia)