William Frederick Denning (1848-1931), British astronomer. Denning was an amateur astronomer who observed numerous comets, planets, meteors and stars. He discovered four comets, and Nova Cygni 1920 (V476 Cyg). He made extensive observations of the surface of Jupiter, and was particularly interested in the planet's Great Red Spot. His observations of Mars led him to support the theories of Italian astronomer Schiaperelli, which described canals on the planet's surface. Denning believed these were of natural origin rather than signs of extra-terrestrial life.