APA (7th ed.) Citation

Koestler, A., & Butterfield, H. (1984). The sleepwalkers: A history of man's changing vision of the universe. Penguin Books.

Chicago Style (17th ed.) Citation

Koestler, Arthur, and Herbert Butterfield. The Sleepwalkers: A History of Man's Changing Vision of the Universe. London [etc.]: Penguin Books, 1984.

MLA (9th ed.) Citation

Koestler, Arthur, and Herbert Butterfield. The Sleepwalkers: A History of Man's Changing Vision of the Universe. Penguin Books, 1984.