The sky around Cave Nebula at true scale, north up and east left, with stars to magnitude 8. The circles show the field of a low-power eyepiece and of 10×50 binoculars.
Cave Nebula is an emission nebula in Cepheus, 2,670 light-years away
Cave Nebula (Caldwell 9, Sh2-155, LBN 529) is an emission nebula in the constellation Cepheus, 2,670 light-years away. spans 50′ × 30′ of sky, about 39 light-years across. It is a telescope object, 6 inches or larger, and it is highest in the evening sky in October.
Nebula: a cloud of gas and dust. Emission nebulae glow on their own, lit by ultraviolet light from hot young stars; reflection nebulae shine by starlight scattered from dust; dark nebulae block the light behind them.
Cave Nebula is Sh2-155 in the Sharpless catalog
Stewart Sharpless listed it in his catalog of H II regions (1959), drawn from the red and blue prints of the Palomar Sky Survey. He rated each region's brightness on a scale of 1 to 3; Sh2-155 is medium (class 2 of 3). It is also listed as LBN 529.
Finding Cave Nebula from ι Cep
Cave Nebula lies 3.8° south of ι Cep, the magnitude 3.5 star. Three fingers held at arm's length cover about 5°.
Cave Nebula is highest in the evening in October
The chart gives its height above the horizon at 9 pm through the year, from 60°N to 40°S. It can be seen from the whole northern hemisphere and south to about 27°S, and never sets north of 27°N.
Cave Nebula is 2,670 light-years away
The light seen from Cave Nebula tonight left it about 2,670 years ago. It ranks 21 of 109 by distance among the 109 Caldwell objects. Distance source: Cep OB3b Gaia DR2, Karnath et al. 2019 (819 pc).
