Mu Cephei is a red supergiant or hypergiant star in the northern constellation Cepheus. It is officially named the Garnet Star; Mu Cephei is its Bayer designation, which is Latinized from μ Cephei and abbreviated Mu Cep or μ Cep. This star appears garnet red and is located at the edge of the IC 1396 nebula. It is a 4th magnitude star easily visible to the naked eye under good observing conditions. Since 1943, the spectrum of this star has served as a spectral standard by which other stars are classified. Mu Cephei is more than 100,000 times brighter than the Sun, with an absolute visual magnitude of −7.6. It is one of the largest known stars with a radius around or over 1,000 times that of the Sun (R☉), and were it placed in the Sun's position, it would engulf the orbits of Mars and Jupiter.

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