Cepheus, also known as the King, is a constellation in the northern hemisphere, named after the mythical King Cepheus of Ethiopia (or Joppa), husband of Cassiopeia and father of Andromeda. Cepheus was originally included among the constellations by the Greek astronomer Ptolemy in the 2nd century, along with other constellations related to the myth of Perseus.
Ptolemy described the celestial king as wearing a crown-like head-dress similar to those worn by Persian rulers. In Greek mythology, Cepheus was descended from the nymph Io, one of Zeus' favourites, which made him worthy of a place among the stars. His kingdom, Ethiopia, was not in Africa, but between the south-eastern Mediterranean shore and the Red Sea. As punishment for his wife's vanity, Cepheus was instructed by an oracle to chain his daughter to a rock and leave her for the sea monster Cetus. Andromeda was saved by Perseus, whom she later married. Cepheus, however, suffered a more tragic fate. Andromeda had been promised to his brother Phineus, who appeared at her wedding with his followers and started a fight. Perseus, outnumbered, took out Medusa's head, turning everyone who looked at it into a stone. The rival and his followers were defeated, but both Cepheus and Cassiopeia looked at the head too. Poseidon placed them both in the sky; Cepheus with his crown, Cassiopeia
, spending half of the year upside down.
The constellation Cepheus occupies an area of 588 square degrees and contains one star with known planets. It can be seen at latitudes between +90° and -10° and is best visible at 9 p.m. during the month of November. Most of the stars in Cepheus are third and fourth magnitude, with many binaries and several interesting variables.
alpha Cephei or Alderamin ("the right shoulder" or "the right arm") is the brightest star in Cepheus. It is an A-type subgiant on its way to becoming a red giant, located near the precessional path of the north celestial pole. Alderamin will become the pole star in about 5,500 years. It last held the position around the year 18,000 BC.
beta Cephei or Alfirk ("the herd" or "the flock") is the second brightest star in the constellation. It is a pulsating variable, a triple star that appears as a visual binary comprised of a blue giant and a faint companion star. The primary component is the brightest star in the Beta Canis Majoris group of variable stars. Alfirk is also the prototype for Beta Cephei variable stars, exhibiting variations in luminosity due to pulsations of its surface. It lies 595 light-years away from Earth.
gamma Cephei, also known as Errai, Alrai or Er Rai ("shepherd") is a binary star about 45 light-years distant. Its primary component is an orange subgiant star believed to be 6.6 billion years old. The companion star is thought to be a red dwarf of similar age. Gamma Cephei will take Polaris’ place as the pole star before Alderamin, around the year 4,000.
delta Cephei or Alrediph or Al Radif ("the follower") is a interesting variable binary star with fine colour contrast. It is a fixed double star, with a yellow giant for its primary component and a blue companion with a visual magnitude of 7.5. Delta Cephei is also a prototype for a class of variables, the Delta Cephei variables, which are useful for measuring distance to outlying galaxies.
mu Cephei is a semiregular variable star, a supergiant of a deep red colour. It was named "Garnet Star" by William Herschel, who admired its appearance. In larger telescopes, mu Cephei also shows an orange element. It is one of the brightest, largest stars observed in the Milky Way.
xi Cephei, also known as Kurhah, Alkirdah, Alkurhah or Al Kirduh, is an attractive triple star. The primary component is a blue-white, ‘metallic’ A-type dwarf and the companion is an F7 dwarf similar in colour. The third component is either an M3 dwarf or a line-of-sight coincidence.
Kruger 60 is a well known binary star approximately 12.9 light-years distant. It consists of two red dwarfs that orbit each other every 44.6 years. The companion is a flare star, occasionally showing flare-ups on the surface.
There are several interesting deep sky objects in Cepheus. NGC 188 is an extremely old globular cluster near the north celestial pole that consists of about 150 stars. It was first discovered by John Herschel in 1825. The cluster is believed to have formed 10-20 billion years ago.
NGC 6939 is an open cluster about 2.5° south of 
theta Cephei. It is composed of about 80 stars. It lies in a very dense area, which is also home to NGC 6946, the Fireworks Galaxy.
The Fireworks Galaxy is a spiral galaxy about 10 million light-years distant, located near the border with the constellation Cygnus
. It can be seen face-on. Observers have spotted nine supernovae in the region.
Cepheus falls into the Perseus family of constellations, along with Cassiopeia
Constellations directly bordering Cepheus are Cygnus
and Ursa Minor