IC 1396 - Elephant Trunk nebula

IC 1396 is an open star cluster in Cepheus associated with an extremely large region of faint nebulosity.

Lying south of the Herschel's blood-red Garnet Star (Mu Cephei), this cluster is extremely large (170' across), very bright (magnitude 3.5), loose, irregular, and awash with a faint nebulous background mixed with dark lanes. At its center is the bright triple Struve 2816, which has a bright white primary and two blue companions. The double Struve 2819 is visible just NE. In a 25mm eyepiece the cluster spills out of the field of view. An O-III filter enhances the nebula's tenuous glow, but nebulosity and dark lanes are also faintly visible without a filter through a 15mm eyepiece.

The nebulosity sprawls across roughly 3 degrees of the sky. It is difficult to see visually, but makes spectacular photographs. The Elephant Trunk nebula is a concentration of interstellar gas and dust within IC 1396. It is a dark, dense globule (vdB 142) with a bright, sinuous rim (IC 1396A). The bright rim is the surface of the dark cloud being ionized the luminous blue star HD 206267, which lies near its center. The entire IC 1396 region is ionized by this massive star, except for dense globules that can protect themselves from the star's harsh ultraviolet rays.

Hundreds of light-years across and about 3,000 light years from Earth, stars are forming in this area. The Elephant Trunk nebula contains several very young stars (less than 100,000 years old) that were discovered in 2003. The combined action of the massive star ionizing the rim of the cloud, and the wind from the young stars at its center blowing outward, generates very high compression in the Elephant Trunk. This is thought to have triggered the formation of protostars.