"Cygnus X-1" is the sixth and final track on Rush's fifth album, A Farewell to Kings.
Cygnus X-1 is an epic about a fictional space voyage to "Cygnus X-1". Inspiration for the story within the song was found in the observation of an X-ray source in the constellation Cygnus. Considered to be one of the most likely black hole candidates in the universe, Cygnus X-1 was discovered in the early 1970s by Canadian scientist Tom Bolton, using the facilities of the David Dunlap Observatory at the University of Toronto. The theme of the track would be continued in "Cygnus X-1 Book II: Hemispheres", the lead and title track of Rush's next album, Hemispheres.
Like "The Necromancer", and the end of "2112", "Cygnus X-1" has an added synthesized voice at the beginning of the song.
In the constellation of Cygnus lies a mysterious black hole that is simply titled "Cygnus X-1" (Cygnus X-1 is believed to be an actual black hole). An explorer aboard the ship "Rocinante" (pronounced ross-in-on-tay) is curious about the black hole and begins to investigate, wondering if an old tale might be true: "Atomized at the core/Or through the astral door/To soar…" As he moves closer, it becomes increasingly difficult to control the ship and he is eventually drawn in by the pull of gravity. His final words in Book I are: "Sound and fury drowns my heart/Every nerve is torn apart."