Bowen, Ira Sprague (1898–1973)

US astrophysicist. He studied the spectra of planetary nebulae and showed that strong green lines in such spectra are due to ionized oxygen and nitrogen under extreme conditions not found on Earth.

The lines had previously been attributed to hypothetical undiscovered elements. In 1927, as a by-product of his work in ultraviolet spectroscopy, Bower identified the strongest ‘nebulium’ (see nebula) lines as due to ‘forbidden’ transitions in the oxygen spectrum. A spectral line is produced when an electron in an atom transfers itself from one energy level to another. Spectral analysis can determine the energy levels between which the electrons are moving, since strong lines are produced where it takes place easily (‘permitted’ transitions) and weak lines where it takes place with difficulty (‘forbidden’ transitions).

Bowen was born at Seneca Falls in New York State and was educated at Oberlin College, Ohio, and the University of Chicago. He joined the California Institute of Technology in 1921, becoming a professor in 1931. He was director of the Mount Wilson and Palomar observatories 1946–64, and was responsible for finishing off the 508-cm/200-in reflector and for designing various of its optical accessories. After his retirement in 1964 Bowen continued to work on optical design problems and was consulted on most of the large-telescope projects begun in the 1960s.