"Cygnus X-1" is a two-part song series by Canadian progressive rock band Rush. The first part, "Book I: The Voyage", is the last song on the 1977 album A Farewell to Kings, and the second part, "Book II: Hemispheres", is the first song on the following album, 1978's Hemispheres. Book I is ten minutes and twenty-five seconds long (10:25), and Book II is eighteen minutes and seven seconds (18:07). It was released as a limited-edition extended play on April 22, 2017.