William Henry Pickering (February 15, 1858 – January 17, 1938) was an American astronomer, brother of Edward Charles Pickering. Not to be confused with William Hayward Pickering, former director of the Jet Propulsion Laboratory.

He discovered Saturn's ninth moon Phoebe in 1899 from plates taken in 1898. He also believed he had discovered a tenth moon in 1905 from plates taken in 1904, which he called "Themis". Unfortunately "Themis" does not exist.

He led solar eclipse expeditions and studied craters on the Moon. He also constructed and established several observatories or astronomical observation stations, notably including Percival Lowell's Flagstaff Observatory.

In 1919, he predicted the existence and position of a Planet X based on anomalies in the positions of Uranus and Neptune but a search of Mount Wilson Observatory photographs failed to find the predicted planet. Pluto was later discovered at Flagstaff by Clyde Tombaugh in 1930, but in any case it is now known that Pluto's mass is far too small to have appreciable gravitational effects on Uranus or Neptune, and the anomalies are accounted for when today's much more accurate values of planetary masses are used in calculating orbits.

He spent much of the later part of his life at his private observatory in Jamaica. He produced a photographic atlas of the Moon: The Moon : A Summary of the Existing Knowledge of our Satellite — New York: Doubleday, Page & Company, 1903.

A crater on the Moon is jointly named after him and his brother Edward Charles Pickering.

External links

Obituaries

• JRASC 32 (1938) 157 (one paragraph)
• MNRAS 99 (1939) 328
• PASP 50 (1938) 122