Complex sentence: There are three red supergiants in the constellation that are visible to the naked eye μ Cephei is known as Herschel's Garnet Star due to its deep red colour.
Split into simpler sentences: There are three red supergiants in the constellation that are visible to the naked eye. The first, μ Cephei, is also known as Herschel's Garnet Star due to its deep red colour.