Sh2-155 is a faint nebula in the constellation Cepheus that is nicknamed the Cave Nebula.
It is one of the rare regions in the sky that show red emission, blue reflection, and dark nebulosity in the same view. It lies 2,400 light-years from Earth.
Image Data:
Telescope/mount: Celestron Compustar C14 with Starizona LF reducer/corrector (f/7.5)
Camera: SBIG STL 11000 with Baader Planetarium Ha, R, G, and B filters
SBIG AO-L adaptive optics at 3 Hz
Location: Pommier Observatory, Portland, OR, USA
Dates: 2017-09-23 through 2017-10-02
Exposures: Ha:R:G:B = 900:95:95:90 = 19 hours 40 minutes total exposure
See additional astrophotographs at www.rodpommier.com