Graduate study in astronomy

John's illness had diminished the family income during the last months of his life. Henry, Hubble's ''impractical'' older brother, lived with his mother and brought home a modest income from his job as an insurance inspector. Bill still pursued his agriculture degree in Wisconsin. Thus, after John's death, the family faced straitened financial circumstances. The situation did not immediately improve with Hubble's return to the United States, for he proved to have less flair for managing money than he thought. He left his friends in England the impression that he had passed the Kentucky bar exam and was practicing law, while in fact he merely did some work translating legal documents.

At the start of the school year in the fall of 1913, Hubble took a job teaching Spanish, physics, and mathematics and coaching boys' basketball at a high school in Indiana, just across the Ohio River from his home in Louisville. He enjoyed unexpected success with the basketball team, taking its members to the state championships, where they took third place. He was also quite popular with the students, who found his English mannerisms intriguing—in contrast to his family members, who found them bizarre. But his heart was not in teaching, and former students recalled that he had difficulty making physics and mathematics accessible, and turned to reading his own astronomy books at every opportunity.

In May 1914, Hubble contacted his former professor, Moulton, asking about financial assistance if he should enter graduate school in astronomy at the University of Chicago. His brother Bill was about to enlist in the army, and would thereafter support the family, forgoing his own dreams and independence. Hubble felt free to move away, and in fact his move back to Chicago marked the beginning of a gradual but eventually complete separation from his mother and siblings.

By the time Hubble made his inquiries about graduate study in Chicago, Hale was long gone from Yerkes Observatory and was monitoring Shapley's and van Maanen's work while carrying out his own solar research at Mount Wilson. Edwin Frost, to whom Hubble also wrote about opportunities for graduate study, had taken his place at Yerkes. On Moulton's recommendation, Frost promptly arranged for a tuition scholarship for Hubble.

Just before he began his graduate instruction at the University of Chicago—which consisted largely of research projects at Yerkes Observatory, rather than coursework in the city — Hubble had the good fortune to attend the August 1914 meeting of the American Astronomical Society. The meeting was held on the campus of Northwestern University in Evanston, where, as a high school student, Hubble had set a state record for high jump. There Hubble heard a landmark presentation by the astronomer Vesto Slipher on the amazing motions of some 40 spiral nebulae, all but a few of which he found to be receding from the Sun at speeds as high as 1100 kilometers per second. Slipher noted these radial motions of galaxies in the same way that Huggins had recorded the radial motions of stars, by looking for a shift to the left or right in the distinctive pattern of spectral lines in the astronomical object compared to the laboratory spectra (see chapter 6, figure 6.4). Slipher carried out his investigation at Lowell Observatory in Arizona, under the guidance of Percival Lowell of Mars as the Abode of Life fame. In part, Slipher's aim was to look for motions within nebulae, as opposed to motions of the nebulae themselves, that might support or refute elements of the Chamberlin-Moulton theory. Even after discovering the spirals' redshifts, Slipher did not give up on the idea that they might be single stars enveloped by nebulous matter. But other astronomers focused on a different aspect of his work: they welcomed his findings as strong evidence that the spirals, whatever they were, did not form part of the Milky Way system, and might in fact be island universes.

The unusual standing ovation Slipher received at the conclusion of his talk at the American Astronomical Society meeting surely helped direct Hubble's thoughts to the mysteries of the spiral nebulae as he considered possible topics for his doctoral dissertation. The spiral nebulae had never been resolved into stars, although some astronomers were aware of stellar spectra collected from the larger, nearer nebulae such as the Andromeda nebula. The velocities of the nebulae were unlike those of any star or cluster in the Milky Way system, implying they lay at a great distance: with such high speeds, any nebulae that were part of the Milky Way system would eventually find their way out. Beyond these facts, no one knew for certain what they were or how far away they might be. Any headway made in answering these questions would put the wise investigator in the company of such great astronomers as William Herschel and William Huggins. Here was fertile ground for Hubble to stake out.

As a lowly graduate student, Hubble could not hope to carry out a major observational program with the 40-inch telescope at Yerkes; he was granted access mostly in his capacity as a research assistant. For his own projects, he resourcefully commandeered a little-used but high quality 24-inch telescope, originally intended for solar work. He fitted it with a camera and began a photographic survey of faint nebulae.

Hubble could not have consulted with Frost about the results of his photographic work, for the unfortunate man was fast losing his eyesight to cataracts. But Hubble could and did turn to a senior astronomer on the staff for help, one of the greatest observational astronomers of his time. Edward Emerson Barnard, a fellow southerner from Tennessee, had grown up in poverty and received only two months of formal schooling. He had learned portrait photography as a trade and eventually found a way to combine this skill with his deep love of astronomy. By the time Hubble met him at Yerkes he counted the Gold Medal of the Royal Astronomical Society among his many awards and medals. He was widely respected for his recent photographs of the Milky Way, including some of ''dark nebulae,'' pointing to the existence of obscuring clouds of material in interstellar space.

For his dissertation research Hubble canvassed the night skies with the 24-inch telescope, capturing the faint nebulae photographically with long exposures. Most of these nebulae were too faint to study spectroscopically, since obtaining a spectrum involves further weakening the light by dispersing or spreading it out through prisms. Information on physical conditions in the nebulae was not Hubble's primary goal, in any case. On a more basic level he wanted to try to characterize them by form and brightness, and to explore their apparent tendency to cluster together in space. In all, Hubble discovered more than 500 previously unknown nebulae of various kinds, the work of thousands of hours at the telescope and in the darkroom.

In the fall of 1916, as Hubble finished up required course-work on campus, he came to the attention of Walter Adams, Hale's right hand man at Mount Wilson and himself a former student of Frost. After a visit to the Chicago campus, Adams wrote to Hale that Hubble might make a fine addition to the staff at Mount Wilson, where the 100-inch telescope would soon be unveiled.

Hale followed up on Adams's suggestion, and in November 1916 offered Hubble the much-coveted position, pending the completion of his dissertation. But in April 1917, Hubble took a remarkable step, considering his life-long desire to become an astronomer and the allure of the world's largest telescope. He asked Hale to defer the start of his Mount Wilson tenure, a request that Hale granted. Hubble had decided to apply for a commission in the Officer's Reserve Corps. He would report for duty on 15 May.

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