Technical details: Location / Date: Outside of Kopparberg, Västmanland, Sweden / 2018-December Optics: Orion Optics UK AG12 Mount: 10 Micron GM1000 HPS (Unguided) Camera: Atik One 6.0 with Astrodon 1,25" RGB Gen 2 E-Series and 5nm H-Alpha narrowband filters Exposure: Ha:119 x 300s bin1x1, R:27 x 180s bin2x2, G:18 x 180s bin2x2, B:14 x 180s bin2x2 (cumulative exposure time is 12 hours and 52 minutes) Processing: Pixinsight and Photoshop   Image details: 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. Sh2-155 is an ionized H II region with ongoing star formation activity, at an estimated distance of 2400 light-years from Earth. Sh2-155 was first noted as a galactic emission nebula in 1959 in the extended second edition of the Sharpless catalogue, being a part of the much larger 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.