The Day We Found the Universe - Marcia Bartusiak [40]
Curtis at the time estimated that our stellar home was some 30,000 light-years wide and contained about a billion stars, with the Sun nicely situated right near the center. He was wrong about that: The Milky Way's dimensions were even then being revised upward, and the Sun was losing its front-row seat on galactic affairs. But Curtis was right about the spiral nebulae being far-off galaxies.
Over the course of that March evening, Curtis laid out his arguments point by point. First, there was the peculiar distribution of the spiral nebulae. If they are stars in the making, he asked, why are there no spirals in the very place where stars are most numerous, the Milky Way? “Occulting matter,” he answered, was masking our view, making it only appear as if the spirals were avoiding the plane of the Milky Way. And then there was the very light of a spiral to consider: The spectrum of a spiral revealed that its light was emanating from a massive assembly of stars, not just a cloud of gas.
His logic was impeccable. Going through the historical records, Curtis determined that nearly thirty “new stars” had made an appearance within the Milky Way over the last three hundred years, each suddenly rising to great luminosity and then sinking back into obscurity once again. But half that number had already been sighted in spiral nebulae in just a few years, making it all the more likely that the “spirals are themselves galaxies composed of hundreds of millions of stars.” Moreover, with the novae being so faint, they had to be situated millions of light-years away. “This is an enormous distance,” admitted Curtis, “but, if these objects are galaxies like our own stellar system, this is about the order of distance at which we should expect them to be placed.”
Curtis was fully aware of the magnitude and complexity of the new cosmic scheme he was proposing. “We know that the relative space in this, our galaxy, occupied by…our solar system … is about the same order as that occupied by a single drop of water in Chesapeake Bay,” he told his audience. “To go still beyond such a concept, the island universe theory forces us to consider a still mightier whole, a space containing hundreds of thousands of stellar universes like our own, each containing millions upon millions of suns… Awe-inspiring as are the concepts of astronomy, this newer concept surpasses them all; it staggers the imagination.” Curtis was plainly carried away by the allure of this astounding idea. His audience was enthralled as well. At the end they applauded with great enthusiasm and kept him long afterward for further discussion.
At the close of the war, officials at the Bureau of Standards had hoped that Curtis would stay with the agency, but he refused. “As to my staying here permanently, I have no idea whatever of doing that,” he assured Campbell. “[I'm] anxious to get back to my hill and the Crossley, and stay there…. I am more than ever of the opinion that men like you [and] Hale…get all the hard knocks, and not half the fun out of life that those of us lower down get.” An observer at heart, he was eager to return to his nebulae. By May 1919, he was back on Mount Hamilton gathering more evidence in support of distant galaxies.
Curtis already had a few converts to his cause. Astronomer Andrew Crommelin of the Royal Observatory in Greenwich favored the island-universe theory as well, but voiced caution: “The hypothesis of external galaxies is certainly a sublime and magnificent one,” he said. “[But] our conclusions in Science must be based on evidence, and not on sentiment.” His fellow astronomers were setting the bar high. Curtis had to provide more than logical arguments to win his case. He needed concrete evidence. Additional clues had been arriving, but they did not originate with Curtis.