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
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.