"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 eight seconds (18:08).

A black hole, known as Cygnus X-1 (an X-ray source believed to be an actual black hole), lies in the constellation Cygnus. An explorer aboard the spaceship Rocinante journeys toward the black hole, believing there may be something beyond it. As he moves closer, it becomes increasingly difficult to control the ship and he is eventually drawn in by the pull of gravity. The final words of Book I describe his ordeal: "Sound and fury drown my heart/Every nerve is torn apart."

The explorer re-enters the story midway through Book II. He has emerged into Olympus, where he witnesses the gods Apollo and Dionysus caught in the struggle between Mind and Heart. Prior to his arrival, the logical thinkers are led by Apollo and the emotional people are ruled by Dionysus. Apollo had shown the people how to build cities and explore the depths of science and knowledge, but Dionysus had lured many of them into the wild forests and provided love. However, his followers do not store any food for the winter and are caught unprepared. A conflict breaks out as the two different ways of life clash.

When he reflects on what he sees, he becomes tormented in the lack of balance of the people who insist on one extreme or the other. His silent scream is felt by the warriors and causes them to rethink their struggle and unite together. The gods recognize the explorer as a nascent new god and name him Cygnus, the God of Balance.

Although the storyline revolves around a science fiction world, it uses Greek mythology to explain the double meaning. "Cygnus X-1" is primarily about the discovery of two conflicting ways of life, and two vastly different ways in which the human mind thinks (logic and emotion are separated into separate sides, or hemispheres, of the brain). The balance point (Cygnus) allows the mind to think with some logic and emotion at the same time, allowing people to be analytical, but not unemotional.

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