James Keeler was the only member of Lick's original astronomical staff with formal training in physics. He was one of a new breed of astronomers—the astrophysicists—who were applying knowledge of the physical world gained in terrestrial laboratories to the stars. Keeler was recruited to the Lick staff as a spectroscopist, a specialist in extracting physical information from the light emitted by a source. Keeler wrote that the light from heavenly bodies "bears the secrets of their constitution and physical condition."

Keeler designed a spectroscope for the 36-inch refractor. With it he made fundamental contributions to our understanding of the clouds of hot gas called emission nebulae, the remnants of dying stars known as planetary nebulae, peculiar stars with emission spectra, and the measurement of stellar velocities—all this with a visual spectrometer.

After a seven-year absence from Mt. Hamilton during which he served as director of Pittsburgh's Allegheny Observatory, Keeler returned as Lick's director in 1898. In the meantime the observatory had been given a 36-inch reflecting telescope by the wealthy English amateur Edward Crossley.

The Crossley reflector in Keeler's time.

The Crossley Reflector was a very large telescope for its time and had excellent optics, but its inferior mounting made it virtually useless for research. Characteristically, Keeler took on putting it into working order himself, leaving the more desirable 36-inch refractor to his staff. He recognized the Crossley's potential as a photographic telescope. After improving the telescope's mounting, Keeler began his epochal deep-space photographs.

Keeler's premature death in 1900 at the age of forty-two cut short a career that was just beginning to reach its full blossoming. Keeler had designed a spectrograph for the Crossley and, had he lived, would have doubtless begun to record the spectra of the "spiral nebulae," perhaps even anticipating some of the discoveries that would make Edwin Hubble famous a generation later.