William George Fastie (6 December 1916 – 14 July 2000) was an American optical physicist and spectroscopist who played a part in the Johns Hopkins University space program of the late 1950s.

[citation needed] He attended Johns Hopkins University between 1934 and 1941, initially at evening classes and later as a graduate student in physics, supervised by August Herman Pfund, Robert W. Wood, and Gerhard Heinrich Dieke.

[citation needed] At the end of the War he joined Leeds & Northrup as a research physicist, but was lured back to Hopkins in 1951 by the professor of physics, John D.

[citation needed] Initially concentrating on spectroscopic analysis of the Earth's upper atmosphere, it soon broadened into a full-fledged astronomy program, using accurately pointed telescopes.

[citation needed] The 'Fastie Finger', a device in the Advanced Camera for Surveys used for masking unwanted bright astronomical light sources used, is named after him.