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

Bowen was born in New York State and graduated from Oberlin College, Ohio. In 1921 he joined the California Institute of Technology, becoming a professor 1931. He was director of the Mount Wilson and Palomar Observatories 1946-64.
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 showed that the strong green lines in the spectra of planetary nebulae are caused by forbidden transitions in known elements under conditions not produced in the laboratory. The lines had previously been attributed to hypothetical undiscovered elements.