The Day We Found the Universe - Marcia Bartusiak (2009)
Chapter 5. My Regards to the Squashes
Roman god. Bringer of War. Fourth planet from the Sun. Astronomers eager to solve the spiral nebulae dilemma had Mars, strangely enough, to thank for a further step toward an answer—at least in a roundabout way.
The red planet, with its vivid ruby luster, has fascinated stargazers for millennia, but interest grew even more intense after the invention of the telescope. With the extra magnification astronomers could at last discern markings on the surface of Mars. Bright patches around its poles, similar in appearance to our own planet's arctic and antarctic regions, were seen to wax and wane with the Martian seasons. So Earthlike was this behavior that by 1784 William Herschel was reporting that Mars “is not without a considerable atmosphere … so that its inhabitants probably enjoy a situation in many respects similar to ours.”
Scrutiny of Mars was particularly favorable in the fall of 1877, when Earth and Mars were at their closest, approaching in their orbits to within thirty-five million miles of each other. The superb viewing conditions allowed the Italian astronomer Giovanni Schiaparelli to catch sight of numerous dark streaks crossing Mars's reddish ochre regions, then known as “continents.” In his native language, he called these thin shadowy bands canali, or “channels,” which many figured arose from natural geographical processes.
But Schiaparelli's term was translated inaccurately, a gaffe that encouraged many fanciful conjectures. The most controversial, by far, was the assumption that the “canals” were irrigation works built by advanced beings, who were directing scarce resources over the surface of their planet for cultivation. “Considerable variations observed in the network of waterways,” wrote French astronomer Camille Flammarion in 1892, “testify that this planet is the seat of an energetic vitality… There might at the same moment be thunderstorms, volcanoes, tempests, social upheavals and all kinds of struggle for life.” No one championed this idea more avidly than Percival Lowell, a wealthy businessman whose crusade generated a Mars mania among the public, so much so that the Wall Street Journal in 1907 reported that evidence for the existence of Martian folk surpassed that year's financial panic as the news story of the year.
Percival Lowell (Lowell Observatory Archives)
Lowell, the oldest of five children, came from a well-established New England family. He was one of the Boston Brahmins, upper-crust Bostonians who had made their fortunes creating the American cotton industry. A few years after graduating from Harvard in 1876, Lowell began to travel extensively, especially to the Far East, which led to his writing several well-received books on the region and its religions. By the 1890s, though, restless and searching for individual expression, he renewed a childhood interest in astronomy. “After lying dormant for many years,” recalled his brother, “it blazed forth again as the dominant one in his life.” Independently wealthy, Lowell decided to establish a private observatory atop a pine-forested mesa nestled against the small village of Flagstaff, Arizona (then still a territory of the United States). His initial aim was to observe the particularly close approaches of Mars occurring in 1894 and 1896. Later, the entire solar system became his celestial playground. He was taking to heart his family's motto—occasionem cognosce, “seize your opportunity.” It was a daring venture for an amateur astronomer with no professional experience, especially since he found himself competing with the new and larger astronomical outposts then being built by universities and research institutions. But in this rivalry, Lowell became the outsider, dedicating his observatory to the pursuit of questions that interested him and him alone. Given his obsession with the red planet, the high perch on which the observatory rested, 7,250 feet above sea level, was soon dubbed Mars Hill.
Lowell devoted the rest of his life to this infatuation. A rugged individualist and showman, he once listed his address as “cosmos” in a friend's guestbook. Though often charming when necessary, the patrician Bostonian could easily become enraged if either his opinions or scientific credentials were challenged. He eventually fired one charter member of his observing staff for continually insisting that the canals on Mars might be illusory after all.
Lowell installed a 24-inch refractor on Mars Hill. Though a modest-sized telescope (by then several others in the world had lens widths of thirty inches or more), it was still perched more than three thousand feet higher than the giant scope at the venerable Lick Observatory, and Lowell sought to outdo his competitor at every turn. Sometimes he tried too hard. Lowell and his staff occasionally reported on sightings—certain elusive stars or markings on planets—that simply weren't there. Lick staffers rolled their eyes in exasperation at the dubious announcements coming out of Flagstaff and hinted that there were defects in Lowell's scope (or with his eyesight). Before long a battle of the observatories ensued—California's top instrument versus Arizona's best. One newspaper headlined the unceasing skirmish as “The Strife of the Telescopes.”
In 1900 Lowell upped the stakes when he ordered a custom-built spectrograph that was an improved version of the one already in use at the Lick Observatory. He directed its manufacturer to make it “as efficient as could be constructed.” To operate it, Lowell hired a recent graduate of the Indiana University astronomy program, Vesto Melvin Slipher, who was grateful to be posted at one of the few observatories in the United States with a large telescope, along with high altitude, clear air, and good “seeing,” minimal blurring from atmospheric activity.
Lowell originally thought of Slipher's job as temporary (“I…take him only because I promised to do so,” Lowell told one of Slipher's professors at Indiana), but the young astronomer ended up remaining until his retirement in 1954, serving as the observatory's director for thirty-eight of those years. Lowell chose well. Slipher took a spectrograph intended for planetary work and with great skill and extraordinary patience eventually extended the observatory's celestial scans far beyond the solar system. Instead of discerning new features on Mars, the observatory's raison d'être, he found himself revealing a surprising facet of the cosmos, previously unknown. He detected the very first hint—the earliest glimmer of data—that the universe is expanding, although it took more than a decade for astronomers to fully recognize just what he had done.
In the nineteenth century, with rural farms in the United States often miles apart, lit by only candle or kerosene, and no interfering glow from a nearby metropolis, the nighttime sky was breathtaking in its appearance. The Milky Way streaked across the celestial sphere like a ghost on the run. This sublime stellar landscape must have been a powerful lure, for many of America's greatest astronomers a century ago were born on Midwest farms, including Slipher. “V.M.,” as he was best known to friends and colleagues, was one of eleven children, and at his school in Indiana he displayed a keen knack for mathematics. Going off to Indiana University at Bloomington at the age of twenty-one, he earned a degree in both mechanics and astronomy. He must have had qualms upon arriving at Flagstaff in the summer of 1901. Before coming to the Lowell Observatory, the biggest telescope he had ever operated was a tiny 4½-inch reflector. He had certainly never handled a spectrograph as large and complex as the one he was expected to operate. It was a daunting task for a beginner. The young man struggled for a year to handle the spectrograph with ease. He even confused the red and blue ends of the spectrum initially, a scientific faux pas of the first magnitude. In distress, Slipher asked Lowell if he could go to Lick to get some instruction, but his boss firmly said no. Given the animosity between the two observatories, Lowell didn't want Lick knowing that one of his staff needed help. “When you shall have learnt all about the spectroscope and can give them as much as you take it will be another matter,” asserted Lowell.
Slipher and Lowell were an intriguing mesh of personalities, like a harmony created from two different notes. Flamboyant, aggressive, and driven in his passions, Lowell hated to share the spotlight, especially when it came to announcing a discovery made at his observatory. Slipher was fortunately Lowell's opposite in character, a man who, it was said, “kept himself well insulated from public view and rarely attended even scientific meetings.” He was a peacekeeper at heart and knew it wasn't wise to steal Lowell's thunder. More than that, he didn't want to. An unassuming and dignified man who always wore a suit and tie to work when not observing, Slipher was markedly deliberate and cautious in his pronouncements. A picture of him at the observatory, fresh from the Midwest, reveals a handsome, dark-haired lad with a gaze and smile like that of Mona Lisa. He preferred to correspond with his peers rather than travel and often had others present his findings. Director and underling, consequently, got along famously.
Young Vesto Slipher (Lowell Observatory Archives)
Frequently away from the observatory, either traveling or taking care of business in Boston, Lowell remained in contact with Slipher via a steady stream of letters and telegrams. While Slipher stood in as the observatory's effective director, Lowell offered his pronouncements from afar on matters astronomical (“Don't observe sun much. It hurts lenses”), administrative (“Permit nobody whatever in observatory office”), and personal (“Will you kindly see if shredded wheat biscuit are to be got at Haychaff”). They consulted each other on hires, equipment, budgets, and even vegetables. Lowell doted on his observatory garden and insisted on news of its condition whenever he was away. “How fare the squashes?” asked Lowell one year as fall harvest approached. His letter the following week closed with, “My regards to the squashes.” And finally, “You may when the squashes ripen send me one by express.”
Slipher did not respond. “Why haven't I received squashes? Express at once if possible,” Lowell anxiously telegraphed right after Christmas. Slipher reluctantly had to answer that the poor gourds, alas, had shriveled up and died.
All was forgiven, though, by next spring. “Thank you for taking so much pains with the garden! Just keep on planting and you will get something,” wrote Lowell. Slipher did; by July he was sending Lowell his latest bounty. “Your vegetables came all right and delighted me hugely,” replied Lowell. More were sent in October.
As with his gardening, Slipher made progress on the spectrograph as well, eventually becoming a virtuoso at its operation. He first used it to verify the rotation periods of Jupiter, Saturn, and Mars. Next was Venus. The planets in the solar system were always Lowell's first priority. Slipher was then directed to use the instrument to analyze planetary atmospheres, an assignment that got him into the thick of Lowell's battles with the astronomical community when he tried to measure whether water vapor was present in the Martian air. Slipher believed he had detected a slight signal, which Lowell immediately publicized as boosting his vision of a watery Mars. But Lick astronomer W. W. Campbell, after conducting the same observation, saw no sign at all of water vapor in the red planet's atmosphere.
Despite the disagreement, Slipher was gaining confidence and improving the sensitivity of the spectrograph through trying out different kinds of prisms and photographic plates. By 1909 he was able to confirm that some gas existed in the seemingly empty space between the stars, a triumph that later won praise from astronomers around the world. These pursuits eventually led Slipher to his greatest discovery of all, an unanticipated revelation that involved the spiral nebulae.
Percival Lowell's 1909 letter directing Vesto Slipher to get
a white nebula's spectrum (Lowell Observatory Archives)
It began innocently enough. On February 8, 1909, Lowell in Boston sent a typed letter to Slipher with concise instructions: “Dear Mr. Slipher, I would like to have you take with your red sensitive plates the spectrum of a whitenebula—preferably one that has marked centres of condensation.” By “white,” Lowell meant a spiral nebula, which in 1909 was still generally understood to be a new planetary system under construction. In a handwritten footnote at the bottom of his note, Lowell stressed that he wanted “its outer parts.” He longed to see if the chemical elements found at a spiral nebula's edge, as revealed by the fingerprints of its spectral lines, matched the composition of the giant planets situated far from our solar system's center. A connection would mean the spirals could indeed be baby solar systems under way.
Slipher balked at first. “I do not see much hope of our getting the spectrum of a white nebula,” he told Lowell. He knew that it would take at least thirty hours to get just a plain old photograph of the nebula with the observatory's 24-inch telescope. Nebulae were extremely faint through its lens. To get a spectrum, with far less light hitting the photographic plate after its passage through the spectrograph, seemed impossible.
But Slipher had something to prove. Campbell at the Lick Observatory had recently written yet another article critical of the Lowell Observatory. It was the latest volley in the observatories' ongoing war over whose refractor could get the better results. Lowell had earlier asserted that the superior air on Mars Hill allowed his 24-inch refractor to see 173 stars in a given field of the sky, where Lick's 36-incher could see only 161. Slipher, deeply loyal to his astronomical home, wanted to settle the matter once and for all. He was eager to set up a challenge between the two observatories, comparing photos of stars taken at the same time on similar plates, but Lowell nixed the idea. To reclaim some honor, Slipher decided to focus on the difficult task of getting the spiral nebula spectrum. “I have come to the conclusion,” he had written John A. Miller, his former astronomy teacher at Indiana, just a few months earlier, “that where we can defend ourselves…we shall have to do it or otherwise everything we publish will be discredited.”
Though Slipher considered the spectral task hopeless, he persisted and by December 1910 was able to wrench some feeble data from the Great Nebula in Andromeda. “This plate of mine,” he informed Lowell by letter, “seems to me to show faintly peculiarities not commented upon.” He was going to say “to show faintly, perhaps” but had scrawled out the “perhaps.” He was now convinced he had captured something on the spectrum previously unseen by other spectroscopists, such as Scheiner in the 1890s.
By trial and error, coupled with an astute technical mind, Slipher started making improvements to the spectrograph. Instead of using a set of three prisms, which better separated the spectral lines, he decided to use just one. Though this made the spectrum more congested and difficult to read, it vastly increased the amount of light available since there was less glass to absorb the incoming photons. More important, he understood that increasing the speed of the camera was vital and so bought a very fast, commercially available camera lens. The entire spectrograph, which included counterweights to keep the telescope balanced, weighed 450 pounds and resembled an oversize nutcracker attached to the bottom of the telescope. The celestial light, instead of going into the eyepiece, was directed to the prism, which separated the beam into its constituent wavelengths. A small photographic plate was suitably positioned to record the spectral lineup, from red to violet.
Planet studies, reports on the return of Halley's Comet, and administrative duties diverted Slipher's attention for a while. He could not get back to the question of the spiral nebula until the fall of 1912. But by then his refashioned spectrograph was operating two hundred times faster than the instrument's original specifications, allowing him to slash his long and tedious exposure times. With his modifications in place, he could at last try for the spectrum that he had so long sought. It was a tantalizing goal, not only scientifically, but personally as well. Two years earlier Lick director Campbell had spoken at Yale University and specifically observed that “there is no more pressing need at present than for a greatly increased number of nebular radial velocities.” To beat Campbell at his own specialty—radial velocities, how fast celestial objects move either toward or away from us as if traveling along a radius—would be sweet triumph indeed for Lowell Observatory loyalists. No one had yet gauged the speed of a spiral nebula. That required a spectrum with more detail than had ever been previously obtained or even deemed possible.
Slipher carried out his first measurement on September 17. It took a total of six hours and fifty minutes for the extremely faint light to fully register. “It is not really very good and I am of the opinion that we can do much better,” he soon relayed to Lowell, “but in view of the results got elsewhere of it generally with much longer exposures, it seems to me encouraging and I mean to try it again.” The spectrum was very tiny, a mere centimeter long and a millimeter wide. The photographic plate itself was barely eight centimeters long, but there was just enough room for Slipher to write “Sept 17 And Neb” on the top of the glass to indicate his target had been the Andromeda nebula.
Gale's Comet required his attention for most of October, so he was not able to get back to Andromeda until November 15. The weather was fair with some clouds, but the wind was strong. He started the measurement at seven that night. Being winter, it was already fully dark, and he worked into the early-morning hours. The plate was exposed for eight hours and was left in the spectrograph, shutters closed, so the following night he could align the telescope once more upon his target and continue the observation for another six hours. By taking the longer photographic exposure and narrowing his slit, he saw some improvement in the spectrum when compared with the one taken in September.
He returned to the problem on December 3 and 4, when the Moon no longer rose at night to interfere with his observation of the dim nebula. This time, Slipher scribbled in his workbook that the transparency of the air was “very good,” underlining it for emphasis. Over the two nights he was able to gather his sparse photons for a total of thirteen and a half hours. The only problem that arose was a troublesome clock drive that took fifteen minutes to fix.
When carrying out these observations, the interior of the wooden dome at times resembled the movie version of a mad scientist's laboratory, with high-voltage induction coils sparking and sputtering by the side of the telescope. A row of old-fashioned Leyden jars provided the ignition. It was a wonder that Slipher didn't electrocute himself. This Rube Goldbergian contraption vaporized samples of iron and vanadium, whose light then served as a calibration for Slipher's measurement. The spectrum of these elements, at rest within the dome, could be compared to the spectrum of the nebula rushing around in space; the difference between the spectra determined the nebula's speed.
Since each spectrum that Slipher produced from Andromeda was so tiny, he needed a microscope to measure how much the spectral lines had shifted, compared to their positions on the calibrated standard. The more the shift, the higher the velocity of the nebula. The microscope had been with Lowell in Boston temporarily, and Slipher didn't get it back until mid-December. But once the scope arrived he couldn't resist taking a quick peek at the Andromeda plates he had so far. There were “encouraging results or (I should say) indications,” Slipher reported to Lowell, “as there appears to be an appreciable displacement of the nebular lines toward the violet.” A shift of the lines toward the blue-violet end of the spectrum meant Andromeda would be moving toward Earth. “I congratulate you on this fine bit of work,” Lowell wrote back.
Vesto Slipher using the spectrograph mounted on Lowell Observatory's
24-inch refracting telescope (Lowell Observatory Archives)
But Slipher felt he needed to acquire an even better spectrum to peg the exact speed. It was an endeavor, he told Lowell, that “would doubtless impress all these observers as a quite hopeless undertaking, and maybe it is, but I want [to] make an attempt.”
He started the final measurement on December 29 at 7:35 p.m. and stayed with it until some clouds rolled in near midnight. On a scale from 1 to 10—1 being the worst, 10 the best—Lowell Observatory astronomers often joked that at 10 you can see the Moon, at 5 you can still see the telescope, and at 1 you can only feel the telescope. Fortunately, the sky was clear the following night, and he was able to collect additional light for nearly seven hours. Perhaps pressing his luck, he went into a third night, New Year's Eve. This time the weather was poor, and he had to finish up just before 1913 rang in. Yet, the additional attempt allowed him to squeeze one more hour of data onto his photographic plate.
Slipher had no time as yet to accurately measure this last plate, but he did a speedy check and right away knew that something was up. “I feel safe to say here that the velocity bids fair to come out unusually large,” he wrote Lowell right away. For Slipher to make such an impetuous claim at such an early stage was downright radical for a man normally so cautious. He must have been thrilled at what he had found.
Throughout January he focused on measuring all four of his plates more carefully, in order to gauge the velocity of Andromeda precisely. He did this by placing the plate of the nebula's spectrum in a “spectrocomparator,” which measured it against the standard spectrum—the rest frame. By turning a screw, he shifted one plate relative to the other. When the spectral lines at last matched, he recorded how much he had to shift the nebula plate to get it in line with the standard. The amount of shift established the velocity of the nebula. His calculations to convert the measured shift into a velocity filled page after loose page, with his figures neatly recorded in pencil. He started on January 7 and ended on the twenty-fourth.
The final result astonished Slipher. The Andromeda nebula was rushing toward Earth at the ridiculous speed of 300 kilometers per second (or around a million kilometers per hour), about ten times faster than Slipher had been expecting, given the average speed of a star in the Milky Way. Nebulae weren't supposed to act like this. Astrophysicists at the time generally believed that nebulae were rather slow cosmic creatures, plodding along at speeds far lower than stars. Instead, spiral nebulae seemed to be in a special class all to themselves. Andromeda was setting a cosmic speed record. In present-day terms, it's nearly forty times faster than a space shuttle in orbit.
Slipher, prudent as always, remeasured the plates he had just taken to make sure there was no error. He also sent a print of the spectrum to Edward Fath to obtain an independent check that the shift was real. In 1908, when Fath had taken his own spectrum of the Andromeda nebula at the Lick Observatory, he too had discovered a shift in its spectral lines. But at the time he simply wrote off the unexpected change as a likely malfunction of his spectrograph. It was the accepted wisdom that celestial objects simply did not move that swiftly. He heedlessly decided to brush aside the anomaly because, as he reported, “the shift has no direct bearing on the question for which an answer was sought.” Again, the hapless Fath missed his chance at making astronomical history. One can imagine his chagrin at receiving Slipher's print. He had seen the same spectral message as Slipher four years earlier, only to ignore it and not follow up.
By February Slipher came to trust both his instrument and his expertise (which in hindsight was truly incredible; today, with far better equipment, astronomers measure Andromeda approaching us at 301 kilometers per second, a difference from Slipher's rate of less than a third of a percent). Slipher informed Lowell that the plates “agree as closely as could be expected and I can not doubt the reality of the displacement.” Andromeda had to be moving at an astounding clip. Instead of announcing the result in a major astronomical journal, though, Slipher chose to publish his brief account—just nine paragraphs—in the Lowell Observatory Bulletin. True to form, Slipher held off on any grander statement until he had secured some confirmation.
Yet even one spiral nebula velocity was an exceptional accomplishment. Many were thrilled for Slipher. “It looks to me as though you have found a gold mine,” wrote Miller, “and that, by working carefully, you can make a contribution that is as significant as the one that Kepler made, but in an entirely different way.”
Max Wolf at the Königstuhl Observatory in Heidelberg admired the spectrum's “beauty.” Edwin Frost, then editor of the Astrophysical Journal, wrote his sincere congratulations at the revelation of such an “incredible” velocity. “It is hard to attribute it to anything but Doppler shift,” he said. “Your success on this object indicates the value of elevation above the sea…. It is a pity that someone cannot try other objects of this sort at elevations of 12,000 to 15,000 ft.” Astronomers would, but only decades later.
Then there were others, such as Campbell at Lick (predictably), who were highly skeptical. “Your high velocity for [the] Andromeda Nebula is surprising in the extreme. I suppose…the error of [your] radial velocity measurement may be pretty large. I hope you have more than one result for velocity.”
To be fair to Campbell, an extraordinary finding like this needed extraordinary proof, and Slipher knew that as well. He had already put out the call for others to try to confirm it. Within a year, Wolf was able to follow up. His spectrum was cruder but still in fair agreement. Soon after, even persnickety Lick Observatory came to confirm Andromeda's fleetness. Lick astronomer William H. Wright obtained a velocity that nearly matched Slipher's. “I had planned to get at this work years ago when Fath got his big displacement… but you seem to have beaten me to it,” Wright told Slipher.
Lowell was enormously pleased. “It looks as if you had made a great discovery,” he wrote, right after Slipher's initial finding. And then the director added, “Try some more spiral nebulae for confirmation.” Slipher took up the challenge with great enterprise, for he was better at following directions than initiating his own scientific pursuits.
Working on Andromeda, though, was a holiday compared to gathering the spectral light from other spirals. Though its center is barely discernible to the naked eye, Andromeda is still the biggest and brightest spiral in the nighttime sky. The others only get progressively smaller and dimmer, which made it even harder for Slipher to obtain their velocity. “Spectrograms of spiral nebulae are becoming more laborious now because the additional objects observed are increasingly more faint and require extremely long exposures that are often difficult to arrange and carry through owing to Moon, clouds and pressing demands on the instrument for other work,” he noted in his work papers. The job for him was “heavy and the accumulation of results slow.”
Slipher's first target after Andromeda was M81, a spiral that is brighter than most, and then he looked at a peculiar nebula situated in the Virgo constellation known as NGC 4594. In his notes, he described it a “telescopic object of great beauty.” It's now popularly known as the Sombrero galaxy for its distinctive resemblance to a Mexican hat viewed from the side. Slipher eventually saw that NGC 4594 was moving at a speed “no less than three times that of the great Andromeda Nebula.” This time, however, the nebula was not traveling toward Earth but instead was whisking away at some 1,000 kilometers per second. Slipher was greatly relieved. Finding a nebula that was racing outward rather than approaching removed any lingering doubts that the velocities might not be real. “When I got the velocity of the Andr. N. I went slow for fear it might be some unheard-of physical phenomenon,” he wrote his mentor Miller. Now, by the spring of 1913, he was reassured that the spectral shifts on his plates reliably meant movement.
At this stage, with just a few measurements in hand, Slipher began to think of the nebulae as drifting by the Milky Way—coming toward us on one side of the galaxy, and wandering away on the other side. He was reluctant to speculate publicly on what the spiral nebulae might be, but he did share some of his pet theories in private correspondence with his astronomer friends. At first he thought they might be dust clouds illuminated by reflected starlight, much the way he had already proven, to great acclaim, how the famous Pleiades star cluster shines. Or maybe, he went on to muse, the spirals were very old stars “undergoing a strange disintegration, brought about possibly by their swift flight through stellar space.” But, even then, he was beginning to have reservations about such interpretations. If the spirals were indeed single stars surrounded by fine matter, Slipher posed in one 1913 letter, why are spirals not “more numerous in, rather than outside, the Galaxy?” That was the very same question Curtis was starting to ask over at the Lick Observatory.
Throughout the succeeding months Slipher kept expanding his list, one spiral at a time. His accomplishment was all the more amazing, considering the relative crudeness of his instrument. Lowell Observatory's 24-inch telescope had only manual controls, ones that weren't yet sophisticated enough for fine guiding. Yet he had to hold the tiny image of each spiral nebula on the slit of the spectrograph with utmost care and steadiness for hours on end as the heavens progressively rotated above him. When asked years later how he was able to do this, Slipher replied dryly, “I leaned against it.” Given the faintness of his targets, his exposures often ran twenty to forty hours, which meant they extended over several nights, even weeks if there was unfavorable weather. And nothing could be done when the Moon was brightly shining. “With such prolonged exposures the accumulation of plates is not very rapid,” he informed Lowell, “but the results are worth while and encouraging,” so much so that Slipher was beginning to feel uncharacteristically possessive of his findings. “It is our problem now and I hope we can keep it,” he told his boss.
Slipher need not have worried. No one else could catch up to him. By the summer of 1914 he had the velocities of fourteen spiral nebulae in hand. And with this bounty of data, an undeniable trend was at last emerging: While a few nebulae, such as Andromeda, were approaching us, the majority were rapidly moving away.
For island-universe devotees this was great news. “My harty [sic] congratulations to your beautiful discovery of the great radial velocity of some spiral nebulae,” wrote Danish astronomer Ejnar Hertzsprung. “It seems to me, that with this discovery the great question, if the spirals belong to the system of the milky way or not, is answered with great certainty to the end, that they do not.” The speeds were simply too great for them to stay put within our home galaxy. But Slipher at this stage was still on the fence. “It is a question in my mind to what extent the spirals are distant galaxies,” he responded.
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.