The Day We Found the Universe (16 page)

For most of his career Slipher published few detailed papers of his work, outside of his observatory's in-house bulletin. He either sat on his data until he was absolutely sure of the results or generously sent his findings to others to use in their analyses. Part of this might have been a reaction to the rumpus the observatory faced whenever Lowell defended his more sensational findings. Slipher inwardly feared that the unwelcome publicity was affecting astronomers' opinions on all other research coming out of Flagstaff. So, he preferred to keep his head down, out of the line of fire, adopting the philosophy, Let the work speak for itself. The singular exception for Slipher was his work on the spiral nebulae velocities. He had worked on so many stellar and planetary spectra that he was absolutely confident of what he was seeing—so confident that he for once overcame his homebound nature and traveled to Northwestern University in Evanston, Illinois, to present his results in person.

In August 1914 sixty-six astronomers from around the United States gathered at Northwestern for their annual meeting, four days of scientific talks, official business, concerts, and social excursions to Lake Michigan. It was the conference when the astronomers unanimously voted to change their title from the Astronomical and Astrophysical Society of America to simply the American Astronomical Society. At the same time, a young man named Edwin Hubble, a graduate student at the Yerkes Observatory, in Wisconsin, was elected for membership.

The presentations were made in the lecture room of the university's Swift Hall of Engineering. Slipher's paper, one of forty-eight read at the meeting, was titled “Spectrographic Observations of Nebulae.” At the start of his talk, Slipher told the audience that he began his investigations simply to obtain a spiral nebula's spectrum, but went on to say that the exceptional velocity of the Andromeda nebula made him shift his attention to the velocities themselves. The average speed of the spirals, he reported, was now “about 25 times the average stellar velocity.” Of the fifteen spiral nebulae he had observed so far, three were approaching Earth, the rest were moving away. The velocities ranged from “small,” as it was recorded on his list, to an astounding 1,100 kilometers per second. That was the greatest celestial speed ever measured up to that time.

When Slipher finished delivering this remarkable news, his fellow astronomers rose to their feet and gave him a resounding ovation. No one had ever before witnessed such a spectacle at an astronomical meeting. And with good reason: Slipher had alone climbed to the top of the Mount Everest of spectroscopy. Even Campbell, his relentless competitor, came to both accept the finding and respect the tremendous effort behind it. “Let me congratulate you upon the success of your hard work,” he wrote Slipher after the meeting. “Your results compose one of the greatest surprises which astronomers have encountered in recent time. The fact that there is a wide range of observed velocities—some of approach and some of recession—lends strong support to the view that the phenomena are real.”

Astronomers at the 1914 American Astronomical Society meeting
in Evanston, Illinois. Vesto Slipher is circled on the left,
Edwin Hubble on the right.
(From
Popular Astronomy,
“Report of the Seventeenth Meeting
,”
1914)

Soon after, Slipher was notified that the National Academy of Sciences in the United States was about to begin publication of a periodical titled
Proceedings
, aimed at displaying the nation's best scientific work. Slipher was asked to contribute an account of his groundbreaking research. “I am…glad to have your kind offer to present my papers to the Academy,” he replied. “It only remains for me to do something worth sending.” Slipher, as usual, was being modest to a fault.

Over the next three years, after he had gathered more spectra, Slipher at last came around to Hertzsprung's view. He, too, began to envision the Milky Way as moving among other galaxies just like itself. He first made this view public before the American Philosophical Society, when he was invited to give a key address at its 1917 annual meeting, one of the nation's most important scientific gatherings. Keen to report on his most up-to-date findings, Slipher even enlisted the help of a mathematician—Elizabeth Williams, in Boston, who had long worked as Lowell's top computer—two weeks before the lecture to help him double-check the direction and magnitude of his full complement of spiral nebulae, now numbering twenty-five. She telegraphed her results in the nick of time.

“It has for a long time been suggested that the spiral nebulae are stellar systems seen at great distances,” said Slipher at the April conference in Philadelphia. “This is the so-called ‘island universe’ theory, which regards our stellar system and the Milky Way as a great spiral nebula which we see from within. This theory, it seems to me, gains favor in the present observations.” With all but four of his twenty-five spiral nebulae racing outward, Slipher speculated at one point that the spirals might be “scattering” in some way, a precocious intimation of the cosmic expansion that took many more years to fully recognize.

Though other astronomers were confirming a few of Slipher's results, the Lowell Observatory astronomer was the absolute ruler in this new celestial realm. He dominated the field for years. By 1925, forty-five spiral nebulae velocities were pegged with assurance, and it was Slipher who had measured nearly all of them. As early as 1915, researchers in Germany, Canada, the United States, and the Netherlands began to look for a pattern in Slipher's growing mound of data. It was an extremely difficult task, though, as the speeds measured for the spiral nebulae were entangled with other velocities, such as Earth's orbital travels and the Sun's journey through the galaxy. It was like trying to determine the exact speed of a train off in the distance, while you yourself are in a car racing down a highway.

The investigators began by subtracting out the extra factors—first the Earth's motion, then the Sun's—to see how fast the spiral nebulae were truly moving. Once these secondary velocities were removed, the astronomers saw that the nebular speeds continued to be enormous, far higher than the average velocity of a star within our galaxy. More important, they confirmed that the mistlike disks were indeed generally headed away from us. A few nebulae, such as Andromeda, were exceptions (they didn't yet know that Andromeda and the Milky Way were gravitationally bound together and so wouldn't be flying away from each other), but all in all the spiral nebulae were primarily moving outward into space in all directions. The German astronomer Carl Wirtz went even further in 1922 by looking at a nebula's size and luminosity to roughly judge which of the nebulae were closer to us and which were farther out. By making this assumption, he noticed a particular progression to the stampede outward: The more distant the nebula, the faster it was receding. That was intriguing.

But perhaps this relationship between speed and distance was a false impression. Maybe the effect would disappear as the velocities of more and more nebulae, especially those found in the southern celestial sky, were measured. It could all average out: half of the nebulae moving toward us, the others away. Astronomers began to worry that what looked like an overall recession might turn out to be a temporary illusion. To take care of this, they began to insert a special component into their equations, a term they labeled
K
, which kept track of the trend. Maybe this term would eventually fade away, but maybe not.

Despite these loose ends, by the time of the 1917 American Philosophical Society meeting, the island-universe theory was rousing from its slumber. Heber Curtis had begun to publish his findings on the spiral nebulae in the major journals, and his cogent arguments in support of distant galaxies were already convincing the top astronomers who counted, such luminaries as Eddington at Cambridge University, in England, Campbell at Lick, and Hertzsprung, then at the Potsdam Observatory, in Germany. The swift velocities that Slipher was finding only strengthened the idea that the spirals were indeed situated far beyond the Milky Way's borders. But success could not be fully grasped until astronomers figured out a method for determining how far away Andromeda and its sister spirals truly were. Nothing could ever be settled in this ongoing debate until someone determined the distances to these exasperating nebulae, in a way that every astronomer had confidence.

What Slipher and Curtis did not yet know was that a novel way to carry out such a celestial measurement had been budding even as they were beginning their researches on the spiral nebulae. It involved a gifted woman with a keen eye, who came upon some intriguing stars while examining photos of an alluring feature in the southern nighttime sky.

It Is Worthy of Notice

F
irst-time travelers to the southern hemisphere might mistake the clouds for high cirrus formations, somehow made luminous in the dark of night. Ancient Persians called the biggest one Al Bakr, or the White Ox. Europeans were introduced to the “two clouds of mist” from accounts of the first circumnavigation of the globe by Ferdinand Magellan and his crew in the early sixteenth century. And so the hazy pair came to be named in honor of the Portuguese-born explorer. The Large and Small Magellanic Clouds are each a chaotic collection of stars, richly diffused with glowing gas.

Such novel and fascinating sights were a compelling reason for European and American astronomers to set up observatories in the southern hemisphere. The Harvard College Observatory did just that in the 1890s, when it established a southern station in the highlands of Peru, just above the town of Arequipa. Before this, for more than a decade, Harvard had been carrying out a formidable task: to catalog every star in the northern sky and accurately gauge its color and brightness. Presented with a sizable endowment for a program in spectroscopy, observatory director Edward C. Pickering resolved to photograph and classify the spectra of all the bright stars as well. The Peruvian observatory allowed Harvard to extend the reach and sweep of this endeavor to the southern sky. By doing this, Pickering was helping astronomy move beyond just tracking the motions of stars across the sky to figuring out their basic properties. Though tedious and wearying, such astronomical surveys can often reveal a few surprises along the way. The Harvard survey was no exception, but it took many photographs to get there.

The Small and Large Magellanic Clouds (top left, bottom left) as seen from
Cerro-Tololo Inter-American Observatory, in Chile. The Milky Way
is on the right.
(Roger Smith/NOAO/AURA/NSF/WIYN)

With the huge number of photographic plates of the northern and southern skies stacking up at the observatory on Garden Street in Cambridge, Massachusetts, Pickering shrewdly recognized the value of smart young women yearning to make contributions in an era that generally denied them full access to scientific institutions. Here was a ready workforce, he noted in one annual observatory report, entirely “capable of doing as much and as good routine work as astronomers who would receive much larger salaries. Three or four times as many assistants can thus be employed, and the work done correspondingly increased for a given expenditure.”