APA (7th ed.) Citation

Allen, D. A., & Allen, C. (1985). Halley, the once-in-a-lifetime comet. Unwin Paperbacks.

Chicago Style (17th ed.) Citation

Allen, David A., and Carol Allen. Halley, the Once-in-a-lifetime Comet. Sydney: Unwin Paperbacks, 1985.

MLA (8th ed.) Citation

Allen, David A., and Carol Allen. Halley, the Once-in-a-lifetime Comet. Unwin Paperbacks, 1985.