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By Root 606 0

at that time was of a contracting nebulous mass that rotated as it contracted, thus giving planets their common plane and direction of revolution about a star, as we see in our own solar system. This is a problem in pattern detection and hypothesis testing to determine if the nebulae patterns represent developing star and planetary systems within our galaxy or island universe galaxies far away. Given his talents for both astrophotography and spectroscopy, it would have been only a matter of time before Keeler conducted a definitive experiment with the Crossley to determine which pattern was real, but he unexpectedly died at age forty-two in August 1900, so that task went to Heber Curtis throughout the 1910s, in the race against the Mount Wilson astronomers for the prize that would ultimately be the universe itself.

Curtis cataloged nebulae by adjective—patchy, branched, irregular, elongated oval, symmetrical—and searched the data for a meaningful pattern that would indicate which hypothesis was correct. He began by rephotographing spirals shot by Keeler years before in hopes of measuring rotation. When he found none he concluded, “the failure to find any evidence of rotation would indicate that they must be of enormous actual size, and at enormous distances from us.” Or, the nebulae are nearby and not rotating. Who could tell? George Ritchey, that’s who, and his long-time-exposure photograph of NGC 6946 in 1917 from the new Hale sixty-inch reflector telescope at Mount Wilson—named after the astronomer George Ellery Hale, who was in the habit of building the world’s largest telescopes and had bagged another one here—revealed a nova that had flared up when compared to earlier photographs of that same object. Comparing this nova to the 1885 nova in Andromeda revealed that it was 1600 times dimmer, which Ritchey took to mean that it was 1600 times farther away. Unless, of course, there are different types of nova, some brighter and some dimmer—which there are—so more data and better theory were still needed. Curtis went to work, photographing nebulae previously imaged and comparing the plates in search of new dots of light. He found them, concluding that one in particular had to be at least twenty million light-years away, which led him to note, “The novae in spirals furnish weighty evidence in favor of the well known ‘island universe’ theory.”15

This might have settled the issue, were it not for the fact that there was no reliable method for measuring distance out that far. As the British astronomer A. C. Crommelin noted in his 1918 comprehensive paper weighing the evidence for and against the island universe theory: “Whether true or false, the hypothesis of external galaxies is certainly a sublime and magnificent one. Instead of a single star-system it presents us with thousands of them, some large and conspicuous, others faint and small through their awful remoteness. Our conclusions in science must be based on evidence, and not on sentiment. But we may express the hope that this sublime conception may stand the test of further examination.”16

Red Shifts and Variable Stars

The “sublime conception” of island universes, however, was not quite ready for prime time. The great British astrophysicist James Jeans developed a model for the evolution of solar systems that looked remarkably like what astronomers thought they were seeing in the nebulae. This model included stars that passed nearby a nebulous cloud, stirring up the particles into spiral shapes that would eventually coalesce into planets. At the Lowell Observatory in Arizona, the colorful and influential astronomer Percival Lowell threw his not inconsiderable weight behind the nebular hypothesis and was steadfastly confident that the fuzzy patches represented solar systems in formation. To bolster his belief he ordered his young charge Vesto Slipher to spectrographically analyze the nebulae to detect the characteristic lines of planets that he strongly suspected would be found within these faint structures, along with their radial velocity—how fast the nebulae were