APA (7th ed.) Citation

Whipple, F. L., & Douglas-Hamilton, D. H. (1965). Brightness changes in periodic comets. Smithsonian Institution Astrophysical Observatory.

Chicago Style (17th ed.) Citation

Whipple, Fred L., and Diarmaid H. Douglas-Hamilton. Brightness Changes in Periodic Comets. Cambridge (Mass.): Smithsonian Institution Astrophysical Observatory, 1965.

MLA (9th ed.) Citation

Whipple, Fred L., and Diarmaid H. Douglas-Hamilton. Brightness Changes in Periodic Comets. Smithsonian Institution Astrophysical Observatory, 1965.