The Day We Found the Universe (14 page)

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
white
nebula—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.