Last night was another good night for imaging, so I decided to try and get in two targets, both of which I haven't imaged before, Caldwell 9 or SH2-155 was my second image which I started at 01:30 and finished at 04:00. I am going to try and do better with this image on the next clear night.
Sh2-155 (also designated
Caldwell 9,
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, though that name was applied earlier to Ced 201, a different nebula in Cepheus. Sh2-155 is an ionized
H II region with ongoing
star formation activity, at an estimated distance of 725 parsecs (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. Although Sh2-155 is relatively faint for amateur observation, some of its structure may be seen visually through a moderately sized telescope under dark skies. Sh2-155 lies at the edge of the Cepheus B cloud (part of the Cepheus
molecular cloud), and is
ionized by young stars from the Cep OB3 association. It has been suggested that radiation from the hot
O-type starHD 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.
The name "Cave Nebula" was coined for this object by
Patrick Moore, presumably derived from photographic images showing a curved arc of emission nebulosity corresponding to a cave mouth. The name was also used earlier to refer to another brighter but unrelated reflection nebula in Cepheus known as Ced 201 or VdB 152, positioned at
R.A.: 22h 13m 27s
Dec.: +70° 15′ 18″ (
2000). The name's application to Sh2-155 has come into vogue through the nebula's inclusion in Moore's
Caldwell catalogue as object Caldwell 9. (
SIMBAD lists the name for Ced 201, but not for Sh2-155.)
@information from Wikipedia
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