RW Cephei is an M-class red hypergiant

Hypergiant

A hypergiant is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.-Characteristics:...

 star in the constellation Cepheus

Cepheus (constellation)

Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...

. One of the largest stars known, RW Cephei is estimated at 1650 solar radii. RW Cephei, while nearly as large as the orbit of Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, is not as large as other stars in the constellation of Cephus

Cepheus (constellation)

Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...

, namely V354 Cephei

V354 Cephei

V354 Cephei is a red supergiant star located within the Milky Way. It is an irregular variable located approximately 9,000 light-years away from our Sun, and is currently considered one of the largest known stars, with a radius estimate of 1520 times that of the Sun, or 1,060,000,000 km...

 and VV Cephei A. RW Cephei is also a semi-regular variable star

Variable star

A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

 of type LC

Irregular variable

An irregular variable is a type of variable star in which variations in brightness show no regular periodicity. There are two main sub-types of irregular variable: eruptive and pulsating.Eruptive irregular variables are divided into three categories:...

. Its surface is subject to pulsations in temperature and luminosity. Over the past 50 to 70 years it has varied from classes

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

G8 to M0 with no discernable pattern.