Sharpless 155: Cave Nebula (narrowband image in HaOIII)
The Cave Nebula (Sharpless 155 or Sh2-155) is a dim and very diffuse bright emission nebula surrounded by dust. It has a radius of about 35 light-years, and is located some 2400 light-years away in the constellation of Cepheus. The nebula got its nickname from the darker area, at the lower middle, which visually appears as a cave.
The name Sharpless comes from a catalog of 312 emission nebulae (H II regions). The first edition was published by Stewart Sharpless in 1953 with 142 objects (Sh1) and the second and final version was published in 1959 with 312 objects (Sh2).
This is my first attempt at a bi-colour narrowband image, using mainly Halpha and a little OIII light. I have added a little RGB just to give realistic star colours. The image is a little orange to my taste, so I will try to revisit it with some SII light next year.
This crescent-shaped star-forming region (HII region) that consists of double ionized hydrogen, lies within and arose from the large molecular cloud known as Cepheus B, which contains reflection, emission, and dark nebulae.
The stars within the Cave Nebula are very young, mostly less than 100,000 years old, while new stars are born at a high rate within the dust clouds of the nebula. Two bright stars (HD 217061 and HD 217086) illuminate the bright ridges of the Cave Nebula.
Orion Optics UK AG16 Astrograph: SBIG 11000 M: Paramount ME2 Mount
R,G,B: 5x3m each; Halpha: 9x10mins; OIII 3x10mins
2hrs 45 min total, all binned 1x1
Processed with CCDStack, Photoshop, Pixinsight
Data capture: January 2016