The Day We Found the Universe - Marcia Bartusiak (2009)
Chapter 8. The Solar System Is Off Center and Consequently Man Is Too
Upon arriving at Mount Wilson, Harlow Shapley had no immediate investigative plans, only a developing interest in variable stars. He had told his Princeton mentor, Henry Norris Russell, that he would probably work on odds and ends. But Shapley's wife, also skilled in astronomy, soon came upon an interesting set of stars while examining photos of a globular cluster. “I have looked at some cluster plates a little,” Shapley wrote Russell, “and found five new variables in the middle of a cluster … or to tell the truth my hausfrau found them but I plan to take the credit for it.” It helped him latch onto a focus; he was going to study the Milky Way's globular clusters, each a dense ball of stars that gleams like a cosmic sparkler frozen in time.
Shapley worked at Mount Wilson from 1914 until 1921, and the best research of his career was accomplished during this time. Shapley was a risk taker. As Hale later noted, “He is much more venturesome than other members of [the Mount Wilson] staff and more willing to base far-reaching conclusions on rather slender data.” Counting up his scientific publications over those seven years, Shapley was the sole author of or a contributor to some 150 notes and papers. Years earlier, none of his childhood friends would have bet on that career outcome, given that Shapley's first job was being a hard-nosed reporter, covering crime and corruption in the Midwest.
Born in 1885, Shapley and his fraternal twin brother, Horace, along with an older sister, Lillian, and a younger brother, John, grew up on a Missouri farm a few miles from the town of Nashville, on the edge of Ozark country not far from where Harry Truman, the thirty-third president, was also born (in 1884). Shapley's father, Willis, was a hay dealer. Young Harlow attended a one-room schoolhouse for a few years but was mostly taught at home. When milking cows, he recited poems by Tennyson to “keep the rhythm going.”
“The St. Louis Globe-Democrat was our chief contact with the outside world,” recalled Shapley. That may be why, at the age of fifteen, he became a reporter for the Daily Sun in Chanute, Kansas, a rough-and-tumble oil town about sixty miles northwest of his family's homestead. He later moved back to Missouri to work on the police beat for the Joplin Times. All the while he spent his free time reading in the local libraries, for Shapley's ambition right from the start was to save enough money to go to college. He eventually applied to the local high school, in order to work toward the diploma he vitally needed to matriculate, but, refused admission due to his meager educational record, he paid out of his own pocket to catch up on his academics at a collegiate prep school. Finishing up in 1907, at the age of twenty-one, he at last qualified for admission to the University of Missouri, just as his schoolteacher mother had always desired.
Given his years of experience reporting on midwestern mishaps, Shapley had always intended to major in journalism, but upon arriving on campus he discovered that the promised opening of the university's School of Journalism had been delayed. “So there I was,” said Shapley later in life, “all dressed up for a university education and nowhere to go. ‘I'll show them’ must have been my feeling. I opened the catalogue of courses and got a further humiliation. The very first course offered was a-r-c-h-a-e-o-l-o-g-y, and I couldn't pronounce it! … I turned over a page and saw a-s-t-r-o-n-o-m-y; I could pronounce that—and here I am!” Shapley, a lover of tall tales since he was a child, was just joking around. He actually was in need of a job, and an offer from Frederick Seares, head of the university's astronomy department, to work for him at 35 cents an hour was likely the deciding factor. In whatever way Shapley came to major in astronomy, the choice suited him to a tee. Seares was mightily impressed by the former reporter, especially the fact, as he put it, that Shapley “thinks about what he is doing.” Within two years Seares had Shapley teaching the introductory astronomy course. Although starting out with little training in physics and mathematics, Shapley ended up in 1910 graduating with honors.
Shapley spent another year at Missouri to obtain his master's degree and chose to go to Princeton for his PhD when he won one of its distinguished fellowships. One of his recommenders had warned Princeton officials to accept this rising star before their competitors had a chance to steal him away. There in the idyllic midlands of New Jersey, under the guidance of Henry Norris Russell, the eminent astronomer and theoretician, Shapley specialized in eclipsing binaries—two stars positioned in such a way that, as they circle, one periodically passes in front of the other when viewed from Earth, causing the binary's light to dim for a while and then rise back. Shapley became a whiz in handling a slide rule and consulting mathematical tables to compute the stars' orbits, as well as their densities and size, Russell's special area of interest. Such work was immensely valuable in confirming the wide range of stellar types, including the existence of giant stars.
Young Harlow Shapley (Photo by Bachrach,
courtesy of AIP Emilio Segrè Visual Archives)
It was an odd pairing of adviser and advisee: Russell, with his stiff and aristocratic demeanor, the son of a Long Island clergyman, coupled with the “wild Missourian” with the round face and farmboy haircut, who once attended two New York City theater performances in one day and judged the experience as “worse than log tables.” But they came to appreciate each other's professional expertise and industriousness. According to Russell's biographer David DeVorkin, the two were often seen strolling the campus together, with Russell using “his cane to sweep the undergraduates out of their path.”
The connections Shapley had made at Missouri proved crucial for his next career step. Seares, his undergraduate professor, had moved to Mount Wilson in 1909 and helped open doors for Shapley to become a staff astronomer at the celebrated observatory. Soon after Hale offered the position in 1912, at a salary of $90 a month plus free board on the mountain. Shapley delayed his start date in order to do some travel in Europe and stay with Russell a bit longer to complete their “crusade” on eclipsing binaries but at last journeyed to Mount Wilson in the spring of 1914. Along the way, he stopped off in Kansas City to marry his University of Missouri sweetheart, Martha Betz, a gifted scholar and linguist he had met in a mathematics class. She took an interest in astronomy once they started dating and even helped him reduce the piles of data he had collected for his doctoral dissertation. On their honeymoon train ride out to California, they together happily computed eclipsing binary orbits. In less than a decade, Shapley had gone from fledgling newsman to professional astronomer, about to look through the eyepiece of what was then the largest telescope in the world.
Conditions at the mile-high observatory were still fairly primitive when Shapley arrived. “Just killed a 3 ft. rattlesnake with 8 rattles lying by our back door,” reported one pioneering staff member. “We had to be rugged in those days,” Shapley later recalled. “We would go up the mountain, a nine-mile hike, sometimes pushing a burro, sometimes not. The new road had not [yet] been put in.” When not on Mount Wilson, Shapley spent his time at the observatory's offices and workshops in Pasadena, a town then in the process of transforming from an agricultural community of lush citrus groves and vineyards to a winter resort town filled with flowers and wealthy visitors from the East.
A sociable fellow, Shapley forged friendships with several colleagues right away, including solar astronomer Seth Nicholson and Dutch astronomer Adriaan van Maanen, the latter of whom first arrived at Mount Wilson in 1911 as a volunteer assistant and remained on as a staff member for thirty-five years. Among these friends and colleagues, Shapley was an incorrigible raconteur. “A discussion with him was like a rousing game of ping-pong, ideas flashing back and forth, careening off at unexpected angles and often coming to earth in a breathless finish,” said Cecilia Payne-Gaposchkin, who knew Shapley later at Harvard. An enormously vain man, Shapley also liked to be flattered and got along best with those who fawned over him. Moreover, he never forgave a slight. “A generous supporter, a stimulating companion, he could also be an implacable enemy,” added Payne-Gaposchkin.
The one person Shapley couldn't sway with his gee-whiz midwestern charm was Walter Adams, the effective leader at Mount Wilson. Hale, prone to nervous breakdowns and bouts of depression, was often gone from Mount Wilson in the 1910s. Sometimes his absences were due to war work, but often because he was recovering from his illnesses. Whenever that happened, Adams was in charge. A proper and dutiful man known for his frugal ways, Adams was so regular in his habits that staffers could “set their clocks by his comings and goings.” An inveterate pipe smoker as well, Adams forged the “Lucky Strike” trail, a shortcut from the observatory to the cigarette stand of the rustic hotel then operating nearby on the mountain. Shapley often grumbled about Adams to his friends. “I feel very sure that if I should go away from here no opportunity would be given me to return so long as Adams has the deciding voice,” Shapley once told a colleague. But the tension between them didn't seem to affect Shapley's innovative work while he was on staff.
The seed for Shapley's groundbreaking research was actually planted before he got to the mountain. While still a Princeton graduate student, Shapley had visited Harvard and there met veteran astronomer Solon Bailey, who suggested to the young man that he use Mount Wilson's new 60-inch telescope “to make measures of stars in globular clusters.” When Bailey was stationed at Harvard's Peruvian outpost in the 1890s, serving as its head, he had begun discovering large numbers of variables, hundreds of them (including Cepheids), in some of the clusters and sensed it was terribly important. He knew that a large telescope, such as the one on Mount Wilson, would be immensely valuable in extending this work. It would have the power to resolve variables in the crowded inner regions of a globular cluster and peg their pulsations.
Shapley ultimately took Bailey's advice and, starting with the variables found by his wife, placed a firm stake in this domain. Shapley and globular clusters quickly “became synonyms” atop the mountain. Shapley's involvement became so intense that he eventually contacted Bailey, to make sure the Harvard astronomer didn't feel Shapley was trespassing on his celestial territory. “I have not intended to intrude upon your field, and I think that you do not feel that I am,” wrote Shapley. “Very much of my work on clusters has been the direct result of my conversation with you in Cambridge three years ago when you suggested the advantages of the Mount Wilson instruments and weather.” Bailey, a kind and gracious man, was in fact delighted by Shapley's joining in. “I hope you will appreciate the fact that I claim no proprietorship in these clusters,” replied Bailey, “but… welcome other investigators in this field.” It was fortunate that he was so affable. Bailey was primarily a data gatherer; Shapley by nature was a bold interpreter, a trait enhanced during his apprenticeship with Russell, who advocated problem-driven research. And that made all the difference in advancing the science.
A globular cluster appears through a telescope as an assembly of brilliant specks of light hovering around a dense and blazing core. With stars packed in like subway commuters at rush hour, the cluster offers a far more exotic celestial environment than our local stellar neighborhood. Alpha Centauri, the star closest to the Sun, is some 4 light-years away. But if the Sun were in the center of a packed globular cluster, it would have thousands of stars closer than that, covering Earth's sky like a sequined blanket visible both day and night. Near misses between stars would be commonplace.
That a globular cluster is a highly spherical collection of stars was not known until the 1600s, with the advent of the telescope. Before that, ancient astronomers simply noted the objects on their sky charts as a “lucid spot” or a lone “hazy star.” Today, these clusters are known to be arranged as a globelike halo, surrounding the disk of the Milky Way somewhat like bees buzzing around a hive. But as late as the 1910s, when Shapley began his observations, astronomers didn't know that, nor exactly how big an individual globular cluster was. Some even pondered if they were island universes in their own right. Shapley himself believed that was true when he was starting out: “It is quite obvious that a globular cluster … is in itself a stellar system on a great scale—a stellar unit which without doubt must be comparable to our own galactic system in many ways,” he wrote in the first paper of his study. Some dabbled with the idea that a spiral nebula was an early stage of a globular cluster about to form: Like an open flower closing at twilight, the spiral over time would fold up into a ball. Shapley's goal was to learn the globulars' true sizes, distances, and compositions and see if such ideas were valid.
Shapley's initial observations were fairly basic. Using the 60-inch telescope, he simply surveyed the colors and magnitudes of the stars in the most prominent clusters. These included Omega Centauri (the biggest of them all), the Hercules cluster, and M3, a globular noted by Charles Messier in 1764. Shapley had no idea where this would lead, but that was standard practice in astronomy: Gather as much data as you can when faced with the unknown and keep your eye out for unusual trends. If anything, Shapley hoped his observations might help Hale in his quest to understand how stars aged and evolved, still quite a mystery to astronomers in the early twentieth century.
Globular Cluster M80
(The Hubble Heritage Team [AURA/STScI/NASA])
As his collection of photographs mushroomed, though, Shapley began to identify Cepheids which he knew would serve as his measuring tape out to the globular clusters. He was quite aware of the paper that Henrietta Leavitt had published just a couple of years earlier and intended to apply it. “Her discovery … is destined to be one of the most significant results of stellar astronomy,” Shapley later wrote to her boss, Pickering.
What was needed was a reliable distance to a Cepheid—any Cepheid, anywhere in the sky—that could serve as the calibration for determining the distances to all other Cepheids using Leavitt's period-luminosity law. That was the beauty of her discovery: Know the distance to just one Cepheid and you know the rest.
Distance measurements have long been a problem for astronomers. To our eye, the celestial sky resembles a dark bowl with pinpoints of light affixed to it—everything appears to be the same distance away. But in reality the stars we see reside at vastly different ranges. Bluish-white Sirius, the brightest star in the heavens, is located 8.6 light-years from Earth; Vega, the prominent summertime star in the constellation Lyra, lies 25 light-years away. How do astronomers arrive at these numbers? “Parallax” is one surveying technique. Parallax is the apparent change in a star's position on the sky when observed first at one end of Earth's orbit and then six months later at the other end (similar to the way an object close by will appear to shift when you view it first with one eye, then the other). By setting the radius of Earth's orbit as a baseline and knowing the angle of shift in the star's parallax, a bit of geometric triangulation determines the star's distance from the Sun directly. Astronomers devised the term parsec to describe the distance between Earth and a celestial object that displays a parallax of one arcsecond of angular measurement on the sky. (One parsec equals 3.26 light-years.) The parallax method is useful out to several hundred light-years. After that, the change in a star's position is too small to be discernible by ground-based telescopes, which is why Leavitt's law was so treasured. It would enable astronomers to extend their distance surveys much farther outward. It would have been nice if a Cepheid resided fairly close to our Sun; then astronomers could have measured the star's parallax and gotten their calibration fairly easily. Unfortunately, there was no Cepheid within reach of a direct parallax measurement from Earth in Shapley's day. Nature was not so accommodating to astronomers. (The closest Cepheid to us is Polaris, the North Star, located about 430 light-years away. Polaris is actually a three-star system, one of which is a large yellow Cepheid that completes its dim/bright cycle every four days.)
The first person to try to confront the Cepheid distance problem was Ejnar Hertzsprung, who had initially recognized that Leavitt's twenty-five variables in the Small Magellanic Cloud were specifically Cepheid stars. He began to look at the Cepheids best studied within the Milky Way, thirteen in all. He couldn't measure their parallax (they were too far away), but he could consult a chronological sequence of astronomical atlases to see how far the stars had moved across the sky, at right angles to our line of sight, in their travels through the Milky Way. It was a matter of determining how their celestial coordinates had changed over the years. Astronomers refer to this advance as a star's “proper motion.” From another type of catalog he looked up how fast they were moving either toward or away from Earth based on the stars' blueshifts or redshifts (a rough gauge of their overall velocity). In an imaginative leap, he then estimated the Cepheid's distance by comparing the star's measured velocity with how fast it appears to be moving across the sky from our far away vantage point. The more distant the star, the slower it seems to journey across the sky. (His actual mathematical procedure, which also involved the Sun's motion through the galaxy, was more complex, but this provides the basic idea.) Hertzsprung's approach in the end provided a crude statistical calibration, one that he then applied to Leavitt's Cepheids in the Small Magellanic Cloud. He concluded that the cloud was 30,000 light-years distant, one of the greatest distances then measured for a celestial object. This demonstrated for the first time the potential power of Leavitt's discovery.
“I had not thought of making the very pretty use you make of Miss Leavitt's discovery,” Henry Norris Russell wrote Hertzsprung when this result came out. Russell had employed a similar technique around the same time, but his aim was to determine the average magnitude of a Cepheid. In the process, he concluded that they were giant stars, far bigger than our Sun. Inspired by Hertzsprung, Russell proceeded to make his own distance calculation to the Small Magellanic Cloud, arriving at 80,000 light-years. Both estimates were highly uncertain and turned out to be far less than current distance measurements (210,000 light-years), but each figure was still astoundingly huge for its day.
Shapley soon adopted Hertzsprung's approach, although he used only eleven of Hertzsprung's thirteen Cepheids in his calibration, suspecting that two of them were peculiar. Just like Hertzsprung, he counted on a simple rule of perspective: The farther away a moving object is located from you, the slower it will appear to travel. A far-off plane seems to crawl along the sky, while a plane closer in going at the same speed would zoom right past you. After estimating an average velocity for a star, Shapley checked how his eleven Cepheids were journeying across the sky. The slower the apparent velocity, the more distant the Cepheid.
It was at this point, though, that Shapley parted company with Hertzsprung. He didn't use Leavitt's period-luminosity relationship, which was based solely on stars in the Small Magellanic Cloud, but instead constructed his own relationship based as well on the Cepheids in the Milky Way, in order to obtain an “improved and extended” period-luminosity law combining both sets of variable stars. He then applied his new rule to the Cepheids found in the globular clusters. He would monitor a Cepheid to peg its period and then calculate the star's distance from his graph.
This worked as long as Shapley could find Cepheids in his globular clusters. Some of the clusters had none at all, as far as he could observe. What they did harbor were variables that were not quite the same. These variables changed quite rapidly, in a matter of hours rather than days or months. There was no guarantee that they behaved in the same way as Leavitt's Cepheids.
Shapley tried mightily to check with Leavitt on this question, writing several times to her boss, Edward Pickering, on whether she had detected fast variables in the Magellanic Clouds and found them to obey her rule. Pickering assured him that photographs were being taken. But progress on the question was occurring at a glacial pace. Pickering was keeping Leavitt busy with work he considered more important. “Routine stuff,” decried Russell to Shapley at one point. “I fear, however, that I am not the man who may justly raise my voice in criticism.”
Eager to move forward, Shapley simply decided to treat his fast variables as if they did follow Leavitt's rule. He extended the Cepheids' period-luminosity relationship to include all these variables, both slow and fast. “This proposition scarcely needs proof,” he had boldly asserted in one early paper, though it was a very controversial decision. But by doing this, Shapley was able to determine the distances to the nearest globular clusters—a formidable task, as the stars were very faint. For clusters farther out, too remote to spot any variables, he resorted to using the brightest stars as distance markers. He just assumed that the brightest stars in a distant globular cluster had a similar magnitude on average to the brightest stars in a nearby cluster. And when the stars themselves could no longer be adequately resolved, he judged distance by the apparent size of the globular cluster in the sky. “The whole line of reasoning… was brilliant,” concluded astronomer Allan Sandage in a review of this technique decades later. Bailey, at Harvard, could have carried out this effort before Shapley, but he was overly cautious about the variables. To him there were too many uncertainties about their nature, so “definite conclusions from these data cannot be safely made,” he reported. Shapley had no such qualms.
But it was yeoman's work, painstaking routines that took four years to complete. Shapley was securing the distance to every Milky Way globular cluster known at the time, sixty-nine in all. With the assistance of Edison Hoge, he took some three hundred photographs. Some exposures were only ten seconds in length, but others lasted up to two hours. Most took minutes. Afterward there was the brutal labor at the work-table analyzing what the images revealed. By 1917 he was writing a colleague that “the work on clusters goes on monotonously—monotonous as far as labor is concerned, but the results are continual pleasure. Give me time enough and I shall get something out of the problem yet.” By then the war was on, but Shapley didn't sign up. He claimed that Hale had convinced him to stay at his job.
Some of the globular clusters (circled) surrounding the Milky Way
(Harvard College Observatory, courtesy of AIP Emilio Segrè Visual Archives)
Shapley didn't particularly enjoy his nights alone with the stars. What drove him back to the telescope month after month were his findings. With the first hint of dawn in the east, as the dome slit slowly closed with a noisome squeal, nearby coyotes would answer in kind with a serenade of high-pitched howls. At night's end, he and the other astronomers would walk back to the Monastery, sometimes whistling a merry tune if the viewing went well and forgetting that they might be disturbing the daytime observers—the solar astronomers—who were still fast asleep. Once in bed themselves, though, the nighttime observers could easily be wakened by the stirrings of the daytime crew. Both sides were together at noontime lunch, which offered the opportunity to settle any squabbles.
Shapley was curious about nearly everything that came his way when on the mountain. “The most unwarranted fun of all comes from bugs,” he wrote a colleague while trapped in a snowstorm on Mount Wilson. “Not that I know much about them, but I am so interested that I would like to turn biologist.” In a way, he did. He began to study the travels of ants around the observatory, noticing that the higher the temperature, the quicker their pace. One species ran fifteen times faster once the Sun heated the insects by an additional 30°C. As he put it, he had discovered the “thermokinetics of ants.” Setting up “speed traps” to gauge the ants' pace precisely, he boasted he could estimate the day's temperature to within one degree by their perambulations. “Another method is to read your thermometer,” he wryly added. His findings were published in scientific journals. For further rest and relaxation, he and his wife climbed all the nearby mountains—little and big—collected plants, and killed any rattlesnakes that came their way.
Between 1916 and 1919 Shapley published his growing body of data on the globular clusters in an extended series of papers, collectively titled “Studies Based on the Colors and Magnitudes in Stellar Clusters.” Each article progressively added another piece to the puzzle. Shapley was taking his reporting skills to a new beat. And in carrying out this endeavor he was ultimately forced to alter his original mental picture of the universe. It began to dawn on Shapley that the Milky Way was far larger than anyone had previously conceived. The first hints arrived when he estimated that some well-known star clusters within the Milky Way were at least 50,000 light-years distant. Later he was finding that the distances to the globular clusters ranged anywhere from 20,000 to 200,000 light-years.
With the globulars acting in a way like surveyor posts, marking the boundaries of our galactic borders, the Milky Way was growing by leaps and bounds. As a result, the globular clusters could no longer be thought of as similar in size to the Milky Way, as Shapley once thought. The clusters were now far smaller by comparison. “This is a peculiar universe” was Shapley's reaction to this new cosmic landscape.
So what did this mean for the spiral nebulae, which Heber Curtis and V. M. Slipher were now enthusiastically hawking as separate galaxies? Around this time Shapley's Mount Wilson buddy van Maanen was claiming to see some spirals rotate, an impossible feat if they were lying at a great distance. To perceive a rotation from so far away over a short period of time would mean the spirals had to be spinning at close to the speed of light!
To understand why this would be so, imagine a kitchen clock sitting right by you on the wall. The second hand is sweeping around the dial at a speed of about 1 centimeter per second. But then imagine the face of that clock covering the entire surface of the Moon, its apparent size looking just like the clock on your wall. Yet the clock in reality is now much bigger, so the second hand has to travel at a faster clip, about 110 miles per second, to make a full circuit over a minute's time. Now if that clock were as big as the Milky Way, the second hand would be moving at a demonic pace. If van Maanen's spiral nebula was truly a distant galaxy and he was able to detect its arms shift over a matter of years, then he was seeing it rotate at light-defying speeds.
Not willing to tolerate such bizarre behavior, Shapley at first was doubtful of van Maanen's finding. In fact, he published an article in 1917 saying that “the minimum distance of the Andromeda Nebula must be of the order of a million light-years,” based on some dim novae detected within the nebula and the faintness of its brightest stars. “The difficulty is obvious,” he continued, “in reconciling van Maanen's measures of internal proper motion with the hypothesis of external galactic systems. We are not prepared to accept velocities of rotation of the order of the velocity of light.” The issue in question was not whether spiral nebulae truly rotate. In the 1910s Vesto Slipher had already detected evidence that they spin around. The proof was found within the spectra of the spirals that he was examining. Like a Frisbee thrown outward and spinning in flight, the rotation on one side is directed forward, adding to the measured velocity, while on the other side the spin is aimed back, subtracting from the overall speed. This difference manifests itself as a slight inclination in the spiral's spectral lines. But this motion was certainly not rapid enough to notice by eye alone when comparing photos taken just a few years apart. Moreover, the spectral signatures indicated that a spiral was closing up, wrapping its arms tighter around the nebula's center, “like a winding spring,” reported Slipher. But this clashed directly with van Maanen's claim that a spiral was opening up. Slipher, so modest and reticent, didn't make an issue of this contradiction. If he had made a clamor, loudly and persistently publicizing his proof, van Maanen's assertions might have been dismissed far earlier. But, as it turned out, Slipher's conflicting result was essentially neglected, occasionally discussed among astronomers privately but rarely singled out in print.
Shapley soon asked his Princeton adviser, Russell, whether he too questioned van Maanen's rotations. “V. M. does a little, Hale a little more, and I much,” wrote Shapley. In time Russell replied that he was “inclined to believe in the reality of the [spirals'] internal proper motions, and hence to doubt the island universe theory. But if [the spirals] are not star clouds, what the Dickens are they?”
Considering what happened soon after the receipt of this letter, Shapley likely took Russell's counsel very, very seriously. As Russell's protégé, he highly respected his former professor's opinion and would have had difficulty ignoring Russell's astronomical advice. It was well known in the community that Russell's “word was law,” which could “make or break a young scientist.” Shapley eventually had a change of heart, a transformation that was triggered not only by Russell's advice but also by the further evaluation of his immense pool of data.
Starting in November 1917 Shapley fired off, with great rapidity, his next group of papers. In his ongoing series on the globular clusters, he completed articles six through twelve in just six months. It was as if he were back at his old newspaper job, pounding out an exclusive on his typewriter to meet a daily deadline. The first of these papers announced his grand goal straightaway: He intended to report on nothing less than “the general plan of the sidereal system…bearing on the structure of the universe.” Shapley made this bold claim because, while trying to make sense of all his data, he had a revelation. He came to believe that his observations were not only refashioning the Milky Way but the universe as well. Unlike many of his fellow astronomers, he was fearless at making extravagant leaps in speculation.
At this stage Shapley had finished slogging through his many observations and calculations and had plotted the positions of the sixty-nine known globulars onto a graph. This provided him with a feel for how they were distributed through space in three dimensions. The result, he noted in paper number seven, was “striking.” Most of the clusters resided in one particular direction, over by the constellation Sagittarius. Like moths lingering by a streetlamp, they were symmetrically arranged about a spot rich in stars and nebulae within our galaxy. It was said the star clouds in this region were so thick that it was “impossible to count every star shown; the images of the faintest stars…merged into one another forming a continuous gray background.” The galactic coordinates for this spot did not match those for our solar system. The globular clusters were not arranged around the Sun at all (as might be expected). Good old Sol was situated off to the side—by Shapley's initial estimate around 20,000 parsecs, or 65,000 light-years away.
Other astronomers had noticed this peculiar distribution of the globular clusters before. In 1909 the Swedish astronomer Karl Bohlin even dared to suggest that the center of the galaxy was in that direction, with the clusters all huddled around it. But no one at the time, including Shapley, took this idea seriously. It was just assumed that the solar system resided in the heart of the galaxy (or close to it). Now Shapley was confirming what Bohlin had suspected all along. His observations forced him to radically alter his original opinion.
From this point on, Shapley's progress was swift. Papers eight through eleven, submitted for publication in December and January, provided the technical details on his methods, assumptions, and calibrations. Shapley knew his conclusion was going to be revolutionary, so he stacked his ammunition with orderly care. Page by page he was stepping toward his grand finale. The full-scale assault took place with paper number twelve, titled “Remarks on the Arrangement of the Sidereal Universe.” This particular article was not fully ready for submission to the Astrophysical Journal until April, in the waning days of World War I, but Shapley couldn't wait that long to spread the news. On January 8, 1918, he wrote the noted Arthur Eddington in England that “now, with startling suddenness and definiteness, [the cluster studies] seem to have elucidated the whole sidereal structure”—in other words, the architecture of the Milky Way. Not only were the globular clusters uniformly scattered around the center of the galaxy, with the Sun shoved off to the hinterlands, but the Milky Way was far larger than anyone had formerly presumed. Shapley now gauged it was an astounding 300,000 light-years from one end of the galactic disk to the other, ten times greater than previous estimates. “You may have been completely prepared for the result,” Shapley told Eddington, “but I was only partially successful as a prophet.”
“While I cannot pretend to have anticipated the view of the stellar system that now seems to be emerging,” responded Eddington, “I do not feel any objection to it either.” This was a confidence booster for Shapley, who was still essentially a rookie in astronomical circles and assuredly grateful for support from such a renowned figure.
Shapley didn't forget to give his boss, George Ellery Hale, then out of town on stressful war business, advance notice as well. “May I impose upon your time for a little while, with an off-hand talk about my astronomical work—divert your attention from earthly troubles to heavenly affairs?” wrote Shapley. The young staff astronomer hardly knew where to begin and for brevity's sake he cautioned Hale that he was leaving out the “probablies, perhapses, maybes, apparentlies, and other such necessary weaknesses in scientific exposition…. So my assumed surety … is neither over-confidence nor a whistling in the dark, but an agreement between us.”
True to character, Shapley fashioned one of his ubiquitous tall tales to present his case to Hale: “The first man, away back in the later Pliocene, who knocked out a hairy elephant with his club, or saw his pretty reflection, or received a compliment, became suddenly conceited (it was a mutation) and there immediately evolved the first reflective thought in the world. It was: ‘I am the center of the Universe!’ Whereupon he took himself a wife, transmitted this bigotry of his germplasm, and through hundreds of thousands of years the same thought without much alteration has been our heritage.” And now, he assured Hale, he would furnish the remainder of the story.
Shapley reminded Hale that he was determining the distances to all the globular clusters then known and was getting ready to publish a series of papers announcing the results: twenty pages of tables, nearly a dozen figures, and around a hundred pages of text in all. For Hale, Shapley summarized his results in three, single-spaced typed pages. The bottom line, he said, was this: The Milky Way is huge, some 300,000 light-years in width, and the Sun is far away from the hub. “Start a messenger on a light-wave down the main highway from the center,” wrote Shapley, and he'd end up at Earth about sixty-five thousand years later. Moreover, he said, “there is no plurality of universes… The galaxy is fundamental in what we call the universe.” True to his impetuous nature, Shapley threw caution to the wind. The Milky Way was now so big, he figured, it had to be the dominant feature of the universe.
When the Milky Way was thought to span only 10,000 or 30,000 light-years, it was easier to think of the spiral nebulae as separate galaxies. But everything changed when Shapley claimed the Milky Way was far larger. If the Andromeda nebula was also a galaxy and with similar dimensions to the Milky Way, its distance would have to be farther out than anyone anticipated to appear as it did on the sky. And that meant that the novae that lighted up within Andromeda's disk were even more luminous than any known physical law could possibly explain. Within a matter of months, Shapley made a complete about-face regarding the spiral nebulae. Once a believer in island universes, Shapley now considered it more reasonable to assume that Andromeda and the other spirals were simply closer: either nestled cozily inside our galactic borders or situated just outside, as smaller outlying colonies. They were no longer the Milky Way's equal in grandeur and power but mere appendages. He even speculated at one point that they might be blobs of nebular material somehow being repelled by the Milky Way at high velocities, perhaps due to radiation pressure or electrostatic forces. As our galaxy travels through space, surmised Shapley, it might be driving “the nearby spirals to either side much as the prow of a moving boat cuts through the waves.”
Formerly suspicious of van Maanen's findings, Shapley now came to like that his friend was detecting the spirals rotate, for it strongly backed his own, newly constructed model of the universe. It meant that the spirals had to be close by, merely secondary members of the Milky Way. Our galaxy reigned supreme. “I believe the evidence is quite against the island universe theory of spirals. I should guess the Andromeda nebula to be not further away than 20,000 light-years,” Shapley told Hector MacPherson, a popular British writer on astronomy.
With all his advance notices and public declarations, the thirty-two-year-old Shapley was crowing and, like a little boy, wanted his elders to notice his cleverness at completely renovating the image of the universe. “The observational problems opened up are unlimited; the amount of stupid measuring ahead of me is almost discouraging,” he told Hale. “But I am enjoying it all except for a considerable nervous strain at the last.”
• • •
Shapley released his findings around the same time that the Mount Wilson Solar Observatory dropped the word solar from its name. Shapley most of all was broadening observations from the mountaintop post to questions far beyond the Sun and into the depths of space and time. What Shapley had done was to hugely extend the Copernican rule. Just as Copernicus in the sixteenth century had removed Earth from the center of the solar system, Shapley relocated the solar system from the heart of the Milky Way. “The solar system is off center and consequently man is too, which is a rather nice idea because it means that man is not such a big chicken. He is incidental—my favorite term is ‘peripheral,’” Shapley bluntly wrote in a 1969 memoir. “If man had been found in the center, it would look sort of natural. We could say, ‘Naturally we are in the center because we are God's children.’ But here was an indication that we were perhaps incidental. We did not amount to so much.”
Shapley had carried out a tour de force, and his findings hit the astronomical community like a lightning bolt. Praise for the work, from the most eminent corners of astronomy, was immediate. After reading Shapley's completed papers, Eddington wrote Shapley that “this marks an epoch in the history of astronomy, when the boundary of our knowledge of the universe is rolled back to a hundred times its former limit.” In a Scientific American article, Russell described the results as “simply amazing.” And British theorist James Jeans told Shapley that his newly published papers were “certainly changing our ideas of the universe at a great rate.”
Mount Wilson astronomer Walter Baade later remarked that he “always admired the way in which Shapley finished this whole problem in a very short time, ending up with a picture of the Galaxy that just about smashed up all the old school's ideas about galactic dimensions. It was a very exciting time, for these distances seemed to be fantastically large, and the ‘old boys’ did not take them sitting down.”
While the news spread quickly within the astronomical community, it took longer to reach the general public, likely due to the shadow of the war and its aftermath. Not until May 31, 1921, did the New York Times report on its front page that Shapley had multiplied the universe's size immensely. Our galaxy, noted the Times reporter, was now 300,000 light-years from end to end, a “super–Milky Way… The young astronomer has proved to his satisfaction by various calculations that the sun, the little speck of light around which a tiny shadow called the earth revolves, is 60,000 light years from the centre of the universe.”
“Personally I am glad to see man sink into such physical nothingness, and it is wholesome for human beings to realize of what small importance they are in comparison with the universe,” says Shapley in the article. (If any readers were made queasy by Shapley's news, the story was conveniently set just above a tiny advertisement for Bell-Ans pills, a popular 1920s indigestion remedy.) The Chicago Daily Tribune published the same announcement on page 1 as if it were entertainment news: Earth, proclaimed the headline, was now a “Rube…Miles Off Sky Broadway.”
Not everyone was convinced of this new cosmic scheme. Critics pointed to several weak points in Shapley's arguments, including Hale, who wondered whether the spirals were something other than Shapley imagined. But the Mount Wilson director still supported Shapley's bravado: “You have struck a trail of great promise…. I think you are right in making daring hypotheses, and in pushing the work ahead as you have done, as long as you…are prepared to substitute new hypotheses for old ones as rapidly as the evidence may demand,” Hale responded to Shapley from his wartime post in Washington. Hale preferred his astronomers to take chances. He didn't want them turning solely into unimaginative data gatherers, as Pickering, at Harvard, was wont to do.
But since Shapley had based his results using such novel methods as the Cepheid beacons and rashly ignored many uncertainties, acceptance was hardly unanimous. Other astronomers had been slowly and methodically measuring the galaxy's dimensions over many years by essentially counting stars, tracing out their distributions and movements over the sky and deep into space. The leader in this endeavor was the highly respected astronomer Jacobus C. Kapteyn, at the University of Groningen in the Netherlands. Though not possessing a good telescope, he organized a massive effort to measure the positions of hundreds of thousands of stars on plates taken at other observatories, partially with the help of state prisoners placed at his disposal. He reached the pinnacle of his life's work when he introduced what became known as the “Kapteyn Universe.” In this model, the largest portion of stars in our galaxy (there was a smaller fraction farther out) were gathered in a space roughly 30,000 light-years wide and 4,000 light-years thick, a sort of squashed football. Moreover, the Sun retained its plum position near the center. But Shapley was declaring that the Milky Way was ten times larger and the Sun pushed far off to the sidelines. It was extremely difficult for Kapteyn and his colleagues to imagine that their time-honored methods for tracking stellar distributions could be so flawed. Others thought so, too. Shapley had constructed a formidable distance ladder outward, but its calibration rested on a measly eleven Cepheids, whose motions were still highly uncertain. If those were wrong, the entire construct toward his fundamental verdict—what he called his “Big Galaxy”—would fall apart like a celestial house of cards. Kapteyn told Shapley that he was “building from above, while we are up from below… When will the time come that we thoroughly mesh?”
Conservative astronomers were most disturbed by the many analytical leaps of faith made by Shapley, who tended to speak, it was said, with a “carnival barker's certainty of truth.” Though brilliant and original, he was often quick to jump to conclusions based on meager observations. Accuracy seemed to be less important to him than developing a broad, grand picture. Walter Adams, for one, was sure that the fast and slow variable stars that Shapley lumped together in his computations were actually “two different breeds of cats.” (He was right; they were later found to be RR Lyrae stars, variables that are less massive and fainter than Cepheids.) And then there was the issue of Shapley's borrowing ideas and techniques from other astronomers without proper acknowledgment. Adams complained to Hale that Shapley “has never given the credit where it belongs.” In one paper published in the Proceedings of the National Academy, Shapley made no mention of either Hertzsprung or Leavitt, who had both certainly paved the way. This infuriated Adams. As one Harvard astronomer later put it, “I have never seen a quicker mind, a more agile sense of humor, or a more complete absence of what usually passes for humility.”
Shapley's critics were right to be cautious. In hindsight, he did get certain things wrong. Astronomers, for example, would later reduce the Milky Way's girth from 300,000 to 100,000 light-years, once they better understood the difference between the fast and slow variable stars and affirmed the presence of interstellar dust, which made celestial objects appear dimmer and hence more distant than they actually were. This made Shapley mistakenly believe that the Milky Way was more extensive than it actually was. Yet even when the galaxy's width was reduced to 100,000 light-years, it was still bigger than Kapteyn and his supporters had been hawking. Shapley's discovery held up over time on the essentials: first of all, that the Milky Way was a far larger metropolis of stars than previously suspected and, second, that the Sun was situated in its suburbs.
Shapley's shift of the Sun's position was fully confirmed in the mid-1920s when Bertil Lindblad, a Swedish expert on stellar dynamics, and Jan Oort, at the Leiden Observatory, in the Netherlands, demonstrated that stars were circulating within the Milky Way around a point situated in Sagittarius, exactly where Shapley had pegged the galactic center. Once Lindblad worked out the theory, Oort rounded up the evidence to prove it. If anyone was still questioning Shapley's pushing the Sun off into the galactic boondocks, Lindblad and Oort swept away all doubts. Like the horse on a carousel, the solar system travels in a continual loop, completing one full circuit around the galactic disk roughly every 250 million years. The last time we were in this neck of the celestial woods, the Appalachian and Ural mountains were just being formed and the dinosaurs were getting ready to rule the Earth.
Shapley's new model of the Milky Way had broad repercussions, especially regarding the spiral nebulae. The idea of island universes, then on the verge of acceptance, was back on shaky ground. “With the plan of the sidereal system here outlined,” reported Shapley, “it appears unlikely that the spiral nebulae can be considered separate galaxies of stars.” There was still the problem of the exceptionally bright novae seen earlier in the spiral nebulae. How do you explain that? asked Shapley. And then there were van Maanen's rotations to take into account. Not everyone was swayed by Shapley's worries; the most ardent believers in external galaxies still held fast to their convictions—not only Curtis but also such major players as Arthur Eddington, W. W. Campbell, and V. M. Slipher. It was the undecideds who were most affected by Shapley's arguments and so remained huddled on the fence. What resulted were two completely different views of the universe, which were difficult to reconcile. The writer MacPherson poetically put it this way: “We may compare our galactic system to a continent surrounded on all sides by the ocean of space, and the globular clusters to small islands lying at varying distances from its shores; while the spiral nebulae would appear to be either smaller islands, or else independent ‘continents’ shining dimly out of Immensity.” As the Roaring Twenties was about to make its appearance, Shapley voted for the “smaller islands,” Curtis for the “continents.”