Born La Salle, Illinois, USA, 10 September 1857
In an era dominated by large refracting telescopes, James Keeler demonstrated the promise and future prospects of reflecting telescopes for conducting astronomical research. His celestial photographs taken with the Crossley reflector demonstrated conclusively that the nebulae, many of them spiral nebulae, existed in much larger numbers than had been previously imagined. Keeler used the spectrograph to measure fundamental physical and chemical properties of celestial objects as a pioneer astrophysicist.
Keeler was the son of William F. and Anna (née Dutton) Keeler. His father, a senior partner in the La Salle Iron Works, had previously been a watchmaker and traveled around the world, after having no success in the California Gold Rush. Keeler grew up in La Salle, Illinois, where he witnessed the total solar eclipse that swept across the United States on 7 August 1869. That event seemingly left a strong impression on Keeler. In November of that year, his family relocated to Mayport, Florida, a move that ended Keeler’s chances for a secondary education.
Keeler developed his interest in astronomy from the practical side of surveying, a skill that he learned from his father. He ordered a 2-in. achromatic lens, and two smaller lenses for eyepieces, from a Philadelphia optical house. Within a week of their arrival Keeler assembled a telescope. In addition to viewing terrestrial objects he observed the Moon, Jupiter, Saturn, nebulae, and other celestial objects. Keeler’s sister, Lizzie, attended a private school in Tarrytown, New York. When she and her classmates observed Saturn through a telescope owned by a local amateur astronomer and philanthropist, Charles H. Rockwell (1826–1904), Lizzie mentioned that she had seen the planet through her brother’s homemade telescope in Florida. Intrigued, Rockwell took it upon himself to finance Keeler’s collegiate education. Keeler further impressed Rockwell by paying for his own passage northward, by assisting his schooner’s captain with celestial navigation.
Rockwell enabled Keeler to gain admittance to the second freshman class at Johns Hopkins University in Baltimore, in December 1877. During his college years, he assisted a research team that viewed the total solar eclipse of 29 July 1878 from Central City, Colorado. Keeler sketched the solar corona with the aid of a 2-in. aperture telescope. This drawing, along with his first scientific paper, was published in the United States Naval Observatory’s report on the eclipse.
After graduating in 1881, Keeler worked as an assistant to Samuel Langley , director of the Allegheny Observatory near Pittsburgh, Pennsylvania. Langley was then perfecting the bolometer, an instrument used to measure total energy, including infrared energy from celestial objects. Keeler and Langley explored this hitherto unknown region of the solar spectrum. Keeler then spent a year of postgraduate study abroad, learning physics under Georg H. Quincke at the University of Heidelberg, and under Hermann von Helmholtz at the University of Berlin. In 1886, he settled at Mount Hamilton, California, site of the new Lick Observatory (then under construction). Keeler spent the next 7 years as a Lick Observatory astronomer, assisting director Edward Holden .
Keeler became one of the pioneers in utilizing spectroscopy to study the composition, temperature, and radial velocities of stars, nebulae, and other celestial objects. His peers considered him to be the leading astronomical spectroscopist of his generation. Along with Langley and several others, he was one of the founders of the new science of astrophysics.
After the 36-in. refractor went into operation at the Lick Observatory in 1888, Keeler used the telescope to measure the wavelengths of emission lines seen in the spectra of nebulae. He went on to demonstrate conclusively that the lines, dubbed nebulium, were not emitted by any known chemical element examined under conditions duplicated in terrestrial laboratories. It took another 30 years before Mount Wilson Observatory astronomer Ira Bowen identified them as the so-called forbidden lines of ionized oxygen, produced under extremely low-density conditions.
In 1891, Keeler married Cora Slocomb Matthews, a niece of the board president of the Lick Observatory trustees. That same year, he accepted an appointment as director of the Allegheny Observatory, after Langley was chosen secretary (director) of the Smithsonian Institution, Washington, District of Columbia.
At Allegheny, Keeler demonstrated that the rings of Saturn are made of individual particles, each traveling with its own orbital velocity around the planet. Using a spectrograph of his own design, and exploiting the principle of the Doppler effect, Keeler measured the speeds of revolution of the ring particles as a function of their distance from the planet. He thus verified the result predicted mathematically by Scottish physicist James Maxwell in 1857. Keeler’s confirmation of Maxwell’s hypothesis was published in the first volume of the Astrophysical Journal (1895) and helped him to garner the Rumford Medal of the American Academy of Arts and Sciences.
At the dedication ceremony of the Yerkes Observatory (21 October 1897), Keeler delivered the main invited address, entitled “The Importance of Astrophysics, and the Relation of Astrophysics to Other Physical Sciences.” This lecture highlighted Keeler’s standing within the American astronomical community and symbolized the growing importance of his subject matter to twentieth-century research practices.
Keeler returned to direct the Lick Observatory in 1898 (succeeding Holden), and refurbished its 36-in. Crossley reflector. With that telescope, Keeler obtained the finest photographs to date of the spiral nebulae, which we know today as distant galaxies. Keeler’s study of the nebulae, which was continued after his death by Lick astronomer Heber Curtis and Mount Wilson astronomer Edwin Hubble , gradually led toward an acceptance of these objects as island universes of stars, lying far beyond the Milky Way.
Along with George Hale , Keeler founded the Astrophysical Journal in 1895, to foster communications among the adherents of what Langley had termed the New Astronomy. He likewise inaugurated the first regular graduate program at the University of California, built around Lick Observatory fellowships, to produce theoretically trained but observationally oriented researchers in astrophysics. Keeler was awarded an honorary Sc.D. by the University of California in 1893, was a recipient of the Henry Draper Medal of the National Academy of Sciences (1899), and was elected to its membership in 1900. That same year, however, he suffered a fatal stroke.