IC 1396 is one of the largest emission nebulae north of the celestial equator in the Constellation Cepheus (The King). It is a vast shell-shaped star forming region nearly 3,000 light-years away in southern Cephei, just 1.5 degree south-southwest of the 4th magnitude orange gem Mu Cephei, also known as Herschel’s Garnet Star, in honour of Sir William Herschel, who was one of the first astronomers to describe it. Mu Cephei, 100,000 times brighter than the Sun, is one of the largest stars known, with a diameter of 2.4 billion miles, or 26 astronomical units; if it were put in place of the Sun, it would extend beyond the orbit of Saturn. It is a a variable star, with a magnitude range of 3.4-5.1. The glow encompasses the sprawling open star cluster Trumpler 37, which lies in the core of the Cepheus OB2 association. Here we have a massive Rosette-type nebula, complete with a central hollow and numerous splotches of dark nebulae littered across its entire face, looking like the Indonesian shadow puppets tossed asunder. One of these bleak featuresis a dark and dense globule on the nebula’s western edge known as the Elephant’s Trunk. It marks one site of active star formation where radiation and winds from the nebula’s hot O-type central star are compressing parts of the cloud and triggering star formation.
Credit: Astrobin, Astronomy.