Mu Cephei (also known as Erakis or Herschel’s Garnet Star) is a red supergiant star in the constellation Cepheus. It was previously considered a hypergiant star until a new estimate of 762 Solar Radii was published for the star. Its alternative name, Garnet Star, was coined when astronomer William Herschel described its color as garnet red. As it is now smaller than Betelgeuse, it is the second largest star visible to the naked eye, smaller than none other than Betelgeuse.
Astronomical data
Radius (in Solar Radii): 762 R☉
Diameter (in Kilometers): 1,060,704,000 km
Mass (in Solar Masses): 11 M☉
Distance (in Light Years): 1,370 ly
Spectral type: M2-la (Red)