The Day We Found the Universe - Marcia Bartusiak [32]
Astronomer Edwin Frost, then nineteen and entering his senior year at Dartmouth College when the nova appeared, recalled the event with great vividness: “[The nova] was in the heart of the Great Nebula…and was a star of about the seventh magnitude. It thus became the only individual star distinguishable in this nebula, which at that time we supposed to be a purely gaseous body… The distance of the nebula was then not regarded as greater than that of the stars in our portion of the Milky Way… Among astronomers, as well as the public generally, it was thought that we might be observing the sudden transformation of the nebula into a star,” and perhaps a planetary system as well. Another great nova, dubbed Z Centauri, appeared in the spiral nebula NGC 5253 a decade later, reinforcing the belief that spiral nebulae were relatively close by. Given what astronomers then knew about stars, there was no other explanation.
So, by the turn of the twentieth century, most astronomers had settled on this common story for the spiral nebulae—that they were new stars and planets emerging. This idea gained momentum when Thomas Chamberlin, a respected geologist, joined up with Forest Ray Moulton, an expert on celestial mechanics, on modeling how the solar system came to be formed. The Chamberlin-Moulton theory suggested that a nomadic star passed near our Sun long ago, drawing out streams of gas. This material eventually became a rotating nebula with spiraling arms, from which the planets slowly condensed. Chamberlin, while working on this idea at the University of Chicago, had heard about the amazing images of spiral nebulae that James Keeler was obtaining with his reflector atop Mount Hamilton, which seemed to suggest that he and Moulton were on to something: The spirals might be the gas, just recently torn off and ready for condensation into the planets that would eventually orbit the star, the bright center of the spiral nebula. Chamberlin wrote Keeler, saying, “[I would deem] it a very great favor to be able to make use of your great harvest of new forms.” Keeler obliged.
“The question whether nebulae are external galaxies hardly any longer needs discussion. It has been answered by the progress of discovery,” declared Clerke with confident finality in her influential book The System of the Stars. “No competent thinker, with the whole of the available evidence before him, can now, it is safe to say, maintain any single nebula to be a star system of coordinate rank with the Milky Way.” To Clerke, such contemplations were “grandiose” and “misleading.” Our galaxy and the universe were one and the same—synonyms in the dictionary of the heavens.
But soon after Clerke wrote her comments, new observations were beginning to suggest something very different. At the Potsdam Observatory, in Germany, Julius Scheiner spent seven and a half hours in January 1899 gathering a spectrum of the Andromeda nebula. What he saw was unexpected. The spectrum did not resemble a cloud of gas, such as the Orion nebula, at all. Instead, it resembled the light emitted by a vast collection of stars. “That the spiral nebulae are star clusters is now raised to a certainty,” reported Scheiner. He began to imagine that the Milky Way itself was a spiral nebula, very similar to Andromeda. But at that point Scheiner was effectively a lone voice in the cosmic wilderness. At the Lick Observatory, Keeler took special note of the German's finding but died before he could follow up.
A further investigation was not undertaken until 1908, when Edward Fath, a graduate student at Lick, used the Crossley telescope to confirm Scheiner's findings on the spectrum of Andromeda (M31), as well as several other spirals, for his dissertation. It was wearying work, as Fath had to sustain a photographic exposure over several nights. One plate was exposed for a total of eight hours and forty-seven minutes. Another took more than eighteen hours. But the