Sh2-155 · Cave Nebula

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Credit T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and… · CC BY 4.0

Chinese name	洞穴星云
Type	Emission nebula
Constellation	Cep
RA	22h57m
Dec	+62°
Apparent magnitude	7.7ᵐ
Hemisphere	Northern
Best season	Autumn
Difficulty	Moderate
Focal length	中长焦 800–1200mm

About

The Cave Nebula (Sh2-155) lies about 2,400 light-years away in Cepheus, named for a curved dark dust band that frames a cave-like opening against bright red hydrogen gas. Sitting on the edge of the large Cepheus B molecular cloud, it is an active H II star-forming region whose bright rim is an ionization front excited by radiation from nearby hot stars, with young stars and protostars embedded within. The nebula combines red emission and blue reflection components, rich in color and layered structure. Of relatively low surface brightness, it suits medium-to-long focal narrowband exposures, making it a rewarding autumn Cepheus target.