The Cepheus Constellation.
Cepheus is a constellation in the northern sky, which is named after Cepheus, a King in the Greek mythology. Cepheus was the King of Ethiopia, married to Cassiopeia and was the father of Andromeda, both of whom are immortalised as modern day constellations. It is one of the 48 constellations listed by the second-century astronomer Ptolemy, and it remains one of the 88 constellations in the modern times. The best viewing month is in October at right ascension 22h 25m and declination 72 degrees 34 sec.
Alpha Cephei, also known as Alderamin, is the brightest star in the constellation, with an apparent magnitude of 2.51. Delta Cephei is the prototype Cepheid variable, a yellow-hued supergiant star 980 light-years from Earth. It was discovered to be variable by John Goodricke in 1784. It varies between 3.5m and 4.4m over a period of 5 days and 9 hours. The Cepheids are a class of pulsating variable stars; Delta Cephei has a minimum size of 40 solar diameters and a maximum size of 46 solar diameters. It is also a double star; the yellow star also has a wide-set blue-hued companion of magnitude 6.3. There are three red giants in the constellation. Mu Cephei also is known as Herschel’s Garnet Star due to its deep red colour. It is a semiregular variable star with a minimum magnitude of 5.1 and a maximum magnitude of 3.4. Its period is approximately two years. The star is around 5.64 AU in radius. If it were placed at the centre of the Solar System, it would extend to the orbit of Jupiter. VV Cephei A is a red supergiant and a semiregular variable star, located at least 5,000 light-years from Earth. It has a minimum magnitude of 5.4 and a maximum magnitude of 4.8 and is paired with a blue main sequence star called VV Cephei B. It is one of the largest stars in the galaxy with a diameter 1,400 times that of our sun. T Cephei, also a red giant, is a Mira variable with a minimum magnitude of 11.3 and a maximum magnitude of 5.2, 685 light-years from Earth. It has a period of 13 months and a diameter of between 329 to 500 solar diameters. There are several prominent double stars and binary stars in Cepheus. Omicron Cephei is a binary star with a period of 800 years. The system, 211 light-years from Earth, consists of an orange-hued giant primary of magnitude 4.9 and a secondary of magnitude 7.1. Xi Cephei is another binary star, 102 light-years from Earth, with a period of 4000 years. It has a blue-white primary of magnitude 4.4 and a yellow secondary of magnitude 6.5.
There are several deep-sky objects in Cepheus. 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. NGC 6946 is a spiral galaxy in which ten supernovae have been observed, more than in any other galaxy. IC 469 is another spiral galaxy, characterised by a compact nucleus, of oval shape, with perceptible side arms. The nebula NGC 7538 is home to the largest yet discovered protostar. NGC 7023 is a reflection nebula with an associated star cluster (Collinder 429); it has an overall magnitude of 7.7 and is 1400 light-years from Earth. The nebula and cluster are located near Beta Cephei and T Cephei. S 155, also known as the Cave Nebula, is a dim and very diffuse bright nebula within a larger nebula complex containing emission, reflection, and dark nebulosity. The quasar 6C B0014+8120 is one of the most powerful objects in the universe, powered by a supermassive black hole equivalent to 40 billion Suns. Credit: Go Astronomy, Wikipedia.