BornMuskegon, Michigan, USA, 27 June 1872

DiedAnn Arbor, Michigan, USA, 9 January 1942

A man of many talents – classicist, linguist, and astronomer – Heber Curtis displayed a keen eye for recognizing the most pressing astronomical problems of his era. After being surpassed on several fronts, Curtis shifted from notable observer to capable administrator, where he continued to guide the research of others. His name appears most often now in connection with the 1920 Curtis-Shapley debate on the distance scale of the universe.

Curtis, elder son of Orson Blair Curtis and Sarah Eliza Doust, moved with his family to Detroit when he was 7. Curtis’s father, a Civil War veteran, had been wounded at the Battle of Fredericksburg but survived the amputation of his left arm. Orson Curtis nonetheless completed his education at the University of Michigan and later secured a position with the United States Customs Service in Detroit. Curtis’s mother, a native of Maidstone, England, was educated at Albion Female Seminary; she was fond of English literature and music.

Curtis graduated from Detroit High School in 1889, where he displayed not only an aptitude for languages but also proficiency with machine tools. He enrolled at the University of Michigan and completed its classical course in 3 years, studying Latin, Greek, Hebrew, Assyrian, and Sanskrit. Curtis’s A.B. degree was awarded in 1892 with Phi Beta Kappa honors; in the following year, he received his A.M. degree. He also studied mathematics but never took an astronomy or physics course from the Michigan curriculum. In 1895, Curtis married Mary D. Rapier; the couple subsequently raised four children.

Curtis’s career, however, was to undergo a dramatic shift, after he was appointed a professor of Latin and Greek at Napa College near San Francisco, California (1894). He began to use the institution’s 8-in. refracting telescope. Two years later, Napa College merged with the University of the Pacific, located near San Jose. Remarkably enough, when a teaching vacancy occurred in mathematics and astronomy at the latter school, Curtis was selected. He sought advice from astronomers at nearby Lick Observatory, who allowed him to spend portions of his summer vacations there as a volunteer assistant. These experiences solidified Curtis’s desire to become a professional astronomer. But shunning the required coursework at Berkeley, Curtis returned to the University of Michigan during one summer (1899) and worked with astronomer Asaph Hall, Jr., on the orbit of newly discovered comet C/1898 F1 (Perrine).

Determined to earn a Ph.D., so as not to be considered merely a displaced classics scholar, Curtis accepted a 2-year Vanderbilt fellowship at the University of Virginia in Charlottesville (1900–1902). Ormond Stone , director of its Leander McCormick Observatory, supervised Curtis’s dissertation (on the definitive orbit of comet C/1898 F1). Curtis also demonstrated his command of astronomical equipment while assisting the Lick Observatory total solar eclipse expedition in 1900. This was the first of 11 such trips of which Curtis was either a member or a leader. After being awarded his degree, he was promptly hired as an assistant astronomer by Lick Observatory director William Campbell and spent 18 productive years at the facility.

Curtis became an active participant in Campbell’s program to measure radial velocities of the brighter stars. Along the way, numerous spectroscopic binary stars were discovered, by the duplicity of their spectral lines. Campbell and Curtis published the first catalog of these stars in 1905. Campbell’s recognition that radial-velocity data should be collected from the entire sky led to his creation of a southern field station erected on San Cristobal Hill near Santiago, Chile. A 37-in. reflector was taken to the site by William Wright and one of the Lick Observatory staff. They were joined by Curtis in 1906, who, along with his wife and children, settled in the Chilean community. Curtis easily learned the native tongue, and at a Pan-American Scientific Congress held in Santiago during 1908–1909, he delivered three papers in Spanish. Curtis might have stayed on indefinitely in Chile had he not been called back to California in 1909 to fulfill another assignment.

Lick Observatory astronomer Charles Perrine , who had continued the photographic study of “nebulae” begun by James Keeler , was appointed director of the Cordoba Observatory in Argentina. Curtis became his replacement and took charge of the 36-in. Crossley reflector, with which the most successful photographs had been obtained. “Nebulae” had been differentiated among other classes into the gaseous “planetary” nebulae and the far more numerous “spiral” or “white” nebulae. Perhaps sensing a less intractable problem, Curtis initially concentrated on the former, comparing their sizes, shapes, and distribution across the sky. While the true nature of these objects and their relationship to stellar evolution remained unknown, Curtis’s detailed study, published in 1918, offered the most complete synthesis of the planetaries to date.

The much larger category of “spiral” nebulae soon attracted Curtis’s attention and provided one of the foremost scientific experiences of his career. Like others of his day, Curtis initially accepted the notion of “spirals” as revolving clouds of matter that were condensing into stars and planetary systems. But a growing body of evidence, both spectroscopic and photographic, was to change Curtis’s mind. As reported by Vesto Slipher , a number of “spirals” exhibited large redshifts, implying rapid motions along the line of sight and seeming to contradict their occurrences as members of the Milky Way system. With one notable exception, “spirals” were distributed rather uniformly across the sky; that anomaly being the plane of our galaxy dubbed the “zone of avoidance.”

Curtis’s study of the “spirals” revealed them in all possible orientations, ranging from face-on to edge-on. The latter exhibited “dark lanes” of dust and gas, which absorbed light from their interiors, and were strongly reminiscent of other “dark” nebulae recognized within the Milky Way itself. To Curtis, it seemed logical that the “spirals” could only be gigantic stellar systems resembling the Milky Way, but lying at enormous distances. Their numbers, he calculated, exceed some 700,000 objects, to the limits of contemporary photography. If the Milky Way were surrounded by a similar ring of dust, then the “zone of avoidance” of the “spirals” could be readily explained. Further evidence came from the occasional appearances of “bright” novae (now recognized as supernovae) in the “spirals.” Curtis began to publish his conclusions in 1917, while employed in wartime duties at San Diego, Berkeley, and Washington. He became the Lick Observatory’s spokesman for the “island universe” theory of “spiral” nebulae – a position that led to his participation in the “Great Debate.”

On 26 April 1920, Curtis and Mount Wilson Observatory astronomer Harlow Shapley were invited to address the annual meeting of the National Academy of Sciences, in Washington, on the “scale of the universe.” Shapley had just found the distances to, and the distribution of, many globular star clusters, which, he argued, swarmed around the Milky Way’s center. The principal outcome of Shapley’s research was his recognition that our Sun was not located near the galactic center, but instead orbited in the outer regions of the galactic disk. For those who accepted Shapley’s conclusions, astronomers’ picture of the Milky Way would never again be the same. Shapley, however, remained a skeptic of the “island universe” theory defended by Curtis and continued to believe that “spirals” were merely condensations of matter lying entirely within his “big galaxy” model. Four years later, Edwin Hubble ’s announcement of a Cepheid variable star within the “Great Nebula” of Andromeda provided definitive support for Curtis’s interpretation of the “spirals” as external galaxies.

Curtis’s interest in solar eclipses provided another venue along which he advanced to the front lines of astrophysical research. Curtis read a scientific paper published in 1911 by Albert Einstein , whose special theory of relativity postulated that light should be deflected at the edge of the Sun by 0.83 arc seconds. Such a measurement could only be conducted during a total solar eclipse, when the Moon’s disk temporarily obscured the Sun itself. Intrigued by this possibility, Curtis published a very credible summary of Einstein’s theory. He also convinced Lick Observatory director Campbell to organize an expedition to observe the next available solar eclipse from Russia in August 1914. The eclipse party brought its long-focus cameras to a site near Kyiv, but it was completely clouded out. To make matters worse, World War I broke out while they were in Russia, and the team could not return to the United States through Germany. The Lick Observatory equipment had to be left in the care of Russian astronomers but was not returned until after the war.

Two years later (1916), in his new general theory of relativity, Einstein announced that the deflection of light at the Sun’s edge was 1.75 arc seconds (or double the amount predicted by his special theory). An observational test of this prediction was sorely needed; the next solar eclipse was to be visible from Goldendale, Washington, in June 1918. Curtis and Campbell had to borrow inferior instruments of shorter focal length, but managed to successfully observe the eclipse. Curtis expended every effort to measure and reduce the results from these plates, but because their scale was considerably smaller, he could neither confirm nor deny the predicted effect. Confirmation of the larger deflection of light was instead obtained at a solar eclipse viewed in 1919, whose results were announced in favor of Einstein’s general theory by British astronomer Arthur Eddington . Only after the Lick Observatory equipment was returned did Campbell and Robert Trumpler obtain still more precise observations during a 1922 solar eclipse. By then, however, Curtis’s golden opportunity had passed.

During the same year (1920) in which he participated in the “Great Debate,” Curtis accepted an appointment as director of the Allegheny Observatory at Pittsburgh. There, he continued the acquisition of stellar parallaxes begun by Frank Schlesinger , despite his own lack of experience in this form of investigation. In retrospect, Curtis’s move effectively marked the end of his most significant contributions to science and appears somewhat puzzling. It must be remembered, however, that attainment of an observatory directorship was then regarded as the pinnacle of an astronomer’s career. By contrast, the inflexible seniority system at Lick Observatory implied that Curtis could not be appointed as director there until he was almost 70. The large salary increase that accompanied such a promotion was no small incentive to Curtis, who had four children to put through college, and likely influenced his decision. Health reasons might have curtailed Curtis’s career as an observer; in later years, he suffered from a progressive thyroid disease that seemingly impaired his immune system.

In 1930, Curtis returned to his alma mater and accepted the directorship of the University of Michigan Observatory. This invitation carried with it an assurance of funding for the construction of a large (98-in.) reflecting telescope. But only 1 year later, support for this venture was withdrawn by the impact of the Great Depression, and the telescope was never built. Its mirror, cast but not fully figured, eventually became the Isaac Newton Telescope, now in the Canary Islands. Instead, Curtis’s energies were largely directed toward development of the McMath-Hulbert Observatory at Lake Angelus, Michigan, where pioneering motion-picture studies of solar phenomena were conducted by Robert McMath .

Curtis’s department produced a number of Ph.D.s during the 1930s, and he himself was instrumental in hiring astronomer Leo Goldberg , who later revived the Michigan program. Curtis’s most notable publication from this era was his lengthy review on “The Nebulae,” published in the fifth volume of the Handbuch der Astrophysik (1933). Treating both galactic nebulae and “spirals,” it adopts a transitional viewpoint en route to acceptance of the expanding universe.

Toward the close of his career, Curtis somewhat reverted to his earlier humanistic interests and coauthored two works addressing issues on science and religion. Although remaining a theist, Curtis declared himself an agnostic on some of the “great unanswered questions” that “may be forever beyond us.” In delivering a keynote address at the dedication ceremony of Philadelphia’s Fels Planetarium, for example, Curtis argued that one of astronomy’s principal attractions was that, “more than any other science, [it] gives us a glimpse of the infinite.”

During his lifetime, Curtis received many honors and distinctions, which included the presidency of the Astronomical Society of the Pacific (1912), vice presidency of the American Astronomical Society (1926), and vice presidency of Section D (Astronomy) of the American Association for the Advancement of Science (1924). He also served on Commission 13 (Solar Eclipses) of the International Astronomical Union.

Over 200 of Curtis’s letters are preserved in the Mary Lea Shane Archives of the Lick Observatory, University of California, Santa Cruz. Additional letters are found in the Archives of Industrial Society, University of Pittsburgh, and in the University of Michigan Historical Collections, Bentley Library, Ann Arbor.