Equinox is the fifth studio album by American rock band Styx, released in December 1975. The lead single "Lorelei" became Styx's second US Top 40 hit.

Styx is an American rock band formed in Chicago, Illinois, in 1972. They are known for blending melodic hard rock guitar with acoustic guitar, synthesizers mixed with acoustic piano, upbeat tracks with power ballads, and incorporating elements of international musical theatre. The band established themselves with a progressive rock sound during the 1970s, and began to incorporate pop rock and soft rock elements in the 1980s.