Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology, and is considered to represent a King. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.
The stars of Cepheus form a shape approximately like a box with a triangle on top. When fainter stars visible Tto the naked eye are included, Cepheus can be interpreted as looking like a king with a crown (upside down with respect to the ecliptic).
Together with other constellations nearby (Andromeda, Perseus, Cassiopeia, and possibly Pegasus), and the constellation Cetus below Cepheus, this may be the source of the myth of the Boast of Cassiopeia, with which it is usually identified.
The most notable star in the constellation is Mu Cephei (μ Cep, μ Cephei), also known as Herschel’s Garnet Star. It is a red supergiant star and one of the largest and most luminous stars known in the Milky Way. It appears garnet red and is given the spectral class of M2Ia.
In time, over the next several hundred thousand years, mu Cephei will run out of fuel in its core and explode as a supernova.
Mu Cephei lies next to the large and faint nebulous region IC 1396 which can be seen in a wide-field telescope or binoculars in very dark sky.
The constellation is also home to some other notable Deep sky objects. NGC 188 is an open cluster that has the distinction of being the closest open cluster to the north celestial pole, as well as one of the oldest known open clusters. The Fireworks Galaxy (NGC 6946) is a spiral galaxy in which nine supernovae have been observed, more than in any other galaxy. The nebula NGC 7538 is home to the largest yet discovered protostar.