The Human Side of Science: Edison and Tesla, Watson and Crick, and Other Personal Stories behind Science's Big Ideas (2016)
Chapter 11: Edwin Hubble and Harlow Shapley Clash/Cooperate over the Universe's Size
Now my own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose.
J. B. S. Haldane1
Since this book is about humans, what human is responsible for these pictures?
Butterfly nebula. NASA, ESA, and the Hubble SM4 ERO Team.
Ring nebula. NASA, ESA, C. R. O'Dell (Vanderbilt University), and D. Thompson (Large Binocular Telescope Observatory).
Hourglass nebula. Raghvendra Sahai and John Trauger (JPL), the WFPC2 science team, and NASA.
EDWIN POWELL HUBBLE
Technically, Hubble didn't take these pictures himself; they are from the Hubble Space Telescope, which was named after him. The next time you're surfing the Internet, you might want to visit Hubble's website for the full-color originals and other lovely color photos that boggle the mind.2 Truly, looking at these images might make you feel puny in comparison to the vast size and complexity of the universe, but it might also make you feel pleased that we human beings have learned a lot about this giant place in which we live.
Since this wonderful telescope bears Hubble's name, it's pretty easy to infer that he must have been the right fellow, at the right place, at the right time, armed with the right instruments. Right.
So, what did Hubble do that led to this giant leap in our understanding of the universe? Let's cut to the chase. In 1929, he wrote a paper titled “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae.” The paper, published in the Proceedings of the National Academy of Sciences, included this graph:
Courtesy of NASA.
That's it. Looks pretty simple, eh? Well, it will take the remainder of this chapter to explain this graph, to introduce the people who contributed to it (both positively and negatively), and to reveal its monster implications for our understanding of the universe.
Let's start with Hubble himself.
EDWIN POWELL HUBBLE (1889–1953)
Virginia Lee James married John Powell Hubble in 1884 in Marshfield, Missouri. Edwin Powell Hubble was the third of their eight children. He seemed to have inherited his mother's good looks and his father's athletic build. As a young child, Hubble had no exceptional qualities, but once he learned to read, he devoured the classics and received high grades in school. The only exceptions were deportment and spelling. Fortunately, deportment grades improved, but spelling remained a sore spot throughout his life. Alas, the mixed blessing of spellcheck came too late for Hubble.
At age ten, he and childhood friend Sam Shelton heard of a lunar eclipse predicted to occur on June 23, 1899. After much pleading from the boys, their parents relented and allowed Sam and Edwin to stay outdoors all night to watch. Sam remembers an unobstructed view and a “magnificent show.” Might this have contributed to Hubble's decision to become an astronomer? Or maybe his career choice was related to his appendicitis at age fourteen. He spent several weeks recovering in bed, reading astronomy books.
Hubble's father traveled a lot, but he ruled the roost with an iron fist when he was home. After his law practice failed, John Hubble went into the insurance business. He became a general agent for the Western Department of Greenwich Insurance Company, responsible for some six hundred agents and adjusters in a four-state area. The family moved several times, landing in Wheaton, Illinois, in time for Edwin to attend high school at Central School. A classmate named Albert Colvin, who lived a block away, said Edwin “acted as though he had all the answers, so there was no intimate contact with him.”3
Academically, Hubble was near the top, but his athletic prowess was even higher. He reached full height during his junior year. He was six feet two inches, a full head taller than all the other boys, save one. At Wheaton Central, he played center on the basketball team. The six-player team was undefeated during the season and won the state championship. In his senior year, he was captain of the track team. In one meet, he won the pole vault, shot put, standing high jump, running high jump, discus, and hammer throw. Between junior and senior year, he worked at a summer job with a surveying crew, and returned ready to become an adult.
At graduation, Superintendent Russell began announcing class honors. “Edwin Hubble, I have watched you for four years and I have never seen you study for ten minutes.” He paused for effect. “Here is a scholarship to the University of Chicago.”
1903 University of Chicago basketball champs; Edwin Hubble at far left. Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California.
At Chicago, Hubble toed a fine line. His father thought astronomy was “outlandish,” so Hubble kept his astronomical studies low-key. The other courses he took were mostly science and math, but they all served as preparation for law school, which was far more pleasing to his father. His athletic activities were curtailed slightly. Hubble loved football and was approached by Amos Alonzo Stagg to play for the University of Chicago. Hubble's father put his foot down, saying there were too many injuries in football. Hubble did some statistical research and pointed out that baseball injuries were just as likely. His father took that as an argument against baseball, so that, too, was banned. Oddly, his father didn't mind boxing, so Edwin Hubble became a well-regarded amateur heavyweight boxer. He also participated in basketball and track, but he played in the shadow of Long John Schommer, a truly gifted athlete who won many All-American honors and led Chicago to two national basketball championships.
The studies went well enough but trailed off a bit toward the end of Edwin's undergraduate days, leaving him with an overall average of B minus. His major distraction was that he had begun to prepare for the Rhodes Scholarship tests. His senior course load included French, Latin, Greek, political economics, and public opinion. He also worked as a lab assistant to physics professor Robert. A. Millikan (winner of the 1923 Nobel Prize in Physics), acted in theatrical productions, and was elected vice president of his senior class. Hubble passed the academic part of the Rhodes Scholarship in good order, and his extracurricular activities and recommendation letters carried the day. He was awarded the 1910 Rhodes Scholarship from Illinois.
In fall 1910, Hubble arrived at Queen's College, Oxford, set to study jurisprudence. In a letter to his sister, he said he had read more than three hundred books over a wide range of subjects, including comparative religion and Russian history. Although it was not discovered until much later, Hubble had spent some time with Herbert Hall Turner, director of the University's Radcliffe Observatory. Contrary to his father's expressed wishes about religion and alcohol, Hubble seldom attended church services and found English ales and French red wines quite interesting. Besides his studies, Hubble also learned the art of rowing, which helped him stay in condition. He also ran track and captained Oxford's baseball team. Holidays were often spent traveling on the Continent, especially Germany, a country that fascinated Hubble. On one such trip, Hubble taught a German naval officer to box, and the officer returned the favor with fencing lessons. Hubble left Germany sporting two small dueling scars, in direct opposition to his father's specific admonition, “In the land and time you will live, the duelist scar is not a badge of honor.”4
Although the letters from home told Hubble none of it, his father's health was deteriorating. The family moved to Louisville, Kentucky, to be closer to his father's office, but that didn't help. It appeared that he had malaria, but it didn't respond to treatment. Finally, it was discovered that he suffered from Bright's disease (a major kidney ailment) for which there is no known cure. Meanwhile, Hubble had completed his degree requirements early and was contemplating studying literature. When he learned of his father's illness, he immediately requested permission to return home. His father was adamant that he finish, fearing Hubble would never have the financial resources to return to England to complete his studies. Since his law degree was secure, Hubble began a less-demanding study: Spanish. In January 1913, Hubble's father died. Hubble learned of this via cable. He later told his mother that he had sought out a clergyman friend and prayed with him at a chapel.
Hubble finished up at Oxford by becoming president of the Cosmopolitan Club, dining with a foreign countess, dancing into the wee hours, and setting up a party on the river for a close friend. In his last letter to his mother from Oxford, Hubble wrote, “I am glad, awfully glad to feel that I am at last going back to help you just as much as I can.”5
When Hubble arrived back home, his siblings were amazed to see how different he looked. He wore knickers, a cape, a wristwatch, and carried a cane. His expressions and pronunciation no longer matched theirs, either. The summer passed quickly, with Hubble possibly translating some Spanish legal papers for a Louisville import company. There is no record of Hubble entering legal practice, and the Kentucky bar exam was first administered in 1919. In the fall of 1913, Hubble took a job teaching Spanish, physics, and mathematics at New Albany (Indiana) High School, just a trolley ride across the river from Louisville. He also coached the basketball team to an undefeated season and a third-place finish in the season-ending state tournament. The New Albany High School students enjoyed his knickers, his cape, and his “Oxford mannerisms,” and Hubble found that “teaching amused him.”6 Perhaps sensing the snare he was about to fall into, Hubble returned to his first academic love. He wrote to his former astronomy professor, Forest Ray Moulton, inquiring about graduate school and financial assistance. Moulton directed Hubble to Edwin B. Frost at Yerkes Observatory in Wisconsin. Frost was in dire need of a good assistant and promised Hubble a small salary and room and board at Yerkes, beginning in October. In a later letter, Frost suggested Hubble come earlier and meet him at the Evanston campus of Northwestern University for the annual meeting of the American Astronomical Society. Forty-eight papers were read at this meeting's sessions, and only one was greeted by a standing ovation. This paper was so pivotal to Hubble's future work that we must interrupt Hubble's biography here.
The paper that caused such a stir at the 1914 American Astronomical Society meeting was titled “Spectrographic Observations of Nebulae,” by V. M. Slipher from the Lowell Observatory in Flagstaff, Arizona. There is a lot of information to unpack here before we can relate it back to Hubble.
Nebulae is the plural of nebula, which is the term used originally to denote any diffuse astronomical object that couldn't be resolved into whatever its constituents might be. An early interest in nebulae came from Charles Messier (1730–1817), who was a comet hunter. As we saw in chapter 2, comets were thought to play a significant role in people's lives, so observers were very interested in comets. Nebulae might be mistaken for comets, so Messier made a list of 110 of them in 1781, so that an astronomer searching for comets would not be distracted. The nebulae were assigned M-numbers by Messier, with the Andromeda Nebula (now known to be the Andromeda Galaxy) called M31.
PERCIVAL LOWELL (1855–1916)
Percival Lowell was the black sheep of the clan, who owned textile factories in Massachusetts. His BA was from Harvard University, in mathematics. At his graduation, he presented a talk on the formation of the solar system. After spending six years in the family business, he began to pursue other interests. First, he fell in love with the Far East. After extensive travels and several books, he turned to astronomy. He then read works by the Italian astronomer Giovanni Schiaparelli, who used the term canali to describe formations on Mars. Although Schiaparelli intended the word to indicate channels, which could be natural formations, it was mistranslated as canals, implying they were constructed by Martians. Using his vast resources, Lowell selected a site at Flagstaff, Arizona, for an observatory and had installed an Alvan Clark twenty-four-inch refractor telescope and a state-of-the-art John Brashear spectrograph. Lowell intended his observatory at Flagstaff to provide evidence for his Martian civilization theories. Lowell's writings of his theories of civilization on Mars, similar to the works of French astronomer Camille Flammarion, inspired many science fiction writers but ultimately produced no physical evidence.
V. M. SLIPHER
V. M. Slipher (1875–1969). Courtesy of LOBS, from Wikimedia Commons.
To operate the instruments at Lowell Observatory, Lowell hired V. M. Slipher (1875–1969). Slipher was born in Mulberry, Indiana, located between Lafayette and Kokomo. He earned a BA in astronomy from Indiana University in 1901 and was known as a meticulous, careful observer. Slipher's observations of the Martian surface never produced convincing proof of canals, but he made many other detailed measurements of planets, stars, and nebulae using the telescope and the spectrograph. The paper he presented at the 1914 meeting of the American Astronomical Society was based on his work with the spectrograph, which revealed an extremely unexpected attribute of nebulae—they were moving, some very fast. How did Slipher measure these velocities? They were based on the Doppler effect.
Many of our own experiences contain examples of the Doppler effect. Think about driving along the highway, minding your own business. Suddenly, you hear a dreaded sound behind you and look into your rearview mirror. Sure enough, it's a police car, siren wailing. You glance at your speedometer. Your speed is within the legal limit now, but how fast were you going when you passed that police car about a mile back? Sweat, sweat. Much to your relief, the police cruiser speeds by. But you notice an odd thing. The sound of the siren was higher-pitched when the car was bearing down on you, then lower-pitched when it was driving away.
This isn't your imagination; it's a real phenomenon, called the Doppler effect. When a sound wave is emitted by a moving source, the frequency heard by a stationary observer is different than the frequency emitted: if the source approaches the receiver, the sound is higher-pitched; if the source moves away from the receiver, the sound is lower-pitched. You hear this same high-pitch, low-pitch pattern as a train goes by, or a race car, or an airplane. The faster the sound source moves, the more noticeable the frequency shift.
The Doppler effect also works for light. If a source of light approaches an observer, the light is shifted toward a higher-frequency end of the spectrum, referred to as a blue shift—a shift toward the blue end of the spectrum; if the source is receding, the light is shifted to a lower frequency, called a red shift—a shift toward the red end of the spectrum. (Think of the visible spectrum as red, orange, yellow, green, blue, and violet, with red as the lowest frequency and violet as the highest.) Since our experience doesn't include extremely fast speeds such as the speed of light, the Doppler effect for light is not noticeable. But, if the amount of frequency shift is measured, the speed of the source can be calculated. Doppler radar is used by weather forecasters to obtain the speed of frontal systems and by baseball observers to find out how fast a pitch travels. Applied to astronomy, the Doppler effect allows the determination of the speed of stars or star groupings. This is what V. M. Slipher did for nebulae that caused such a stir at the American Astronomical Society meeting.
BACK TO HUBBLE
The newly minted American Astronomical Society member and neophyte graduate student Edwin Hubble witnessed V. M. Slipher's presentation on the velocities of faint nebulae. The fact that most nebulae were moving away from us and at extremely high speeds impressed everyone there. The nature of these nebulae was still an open question, as was the size of the Milky Way Galaxy and the size of the whole universe. The cutting-edge position of nebulae on the future of astronomy held tremendous appeal for Hubble.
The next two years at the Yerkes Observatory played right into Hubble's interest. Yerkes was short of staff, having lost several astronomers to the new telescope being built by George E. Hale, the hundred-inch device at Mount Wilson (much more about that later). The other crippling blow was that the director, Edwin B. Frost, suffered from cataracts. He couldn't use the telescope at all and even had to have his mail read to him by Hubble and the other graduate students. Besides taking his turn using the forty-inch refractor in velocity studies, Hubble had almost total use of a twenty-four-inch reflector telescope, and he collected data for his dissertation, “Photographic Investigations of Faint Nebulae.” Along the way, he detected a bulge in a nebula NGC 2261. (NGC stands for New General Catalogue of Nebulae and Clusters of Stars, one of many star catalogs, about which, more later.) This provided nice material for an article in the prestigious Astrophysical Journal.
Toward the end of 1916, things began to move very rapidly for Hubble. He had enough data to finish his thesis, and he began writing it. Then, a job offer came from George Hale to work at Mount Wilson, contingent on completing his degree. Next, the United States entered World War I. Hubble hurried his thesis along (perhaps a little too quickly) and volunteered for the war effort. Frost was running out of funding to support Hubble anyway, so he recommended that he take the Mount Wilson job as he helped expedite the thesis. Hubble then wrote to Hale, told him of his service plans, and asked him if the job would still be his after the war. Hale said yes.
In May 1917, Hubble entered the US Army Reserve Officer training program at Fort Sheridan, on Lake Michigan. He chose the infantry and was requested to teach marching by the stars. In August, Hubble was awarded his captain's bars and ordered to active duty. He was assigned to Camp Grant in Illinois and was made commander of the 2nd Battalion, 343rd Infantry Regiment. Training continued during the fall and brutal winter. In January 1918, Hubble was promoted to major, and in July, he was examined and found fit for overseas duty. Deployment to Europe didn't happen until September, and the slow, stormy crossing was extremely difficult, with the threat of U-boats always present. From England, quite different from when Hubble had last seen it almost five years earlier, the 343rd was ferried across the English Channel to France. After training at combat schools, the unit was almost ready to join the war, but the Germans were pushed back and surrendered in October. Hubble said, “I barely got under fire and altogether I am disappointed in the matter of the war.”7 Hubble served several months with occupation forces, then wound up in Cambridge. There, he sat in on a class taught by Arthur Eddington (see chapter 10) and made the acquaintance of astronomer H. F. Newall, who proposed Hubble for membership in the Royal Astronomical Society. In June, Hubble wrote Hale that he was almost ready to return home. Hale responded, “Please come as soon as possible, as we expect to get the 100-inch into commission very soon, and there should be abundant opportunity for work by the time you arrive.”8 Hubble sailed in August, mustered out of the army in San Francisco, and stopped for a short visit to Lick Observatory, near San Jose. The astronomers were a bit thrown by his accent and uniform, and addressed him as “Major Hubble” from then on. He continued traveling south and became an official staff member of the Mount Wilson Solar Observatory on September 3, 1919, probably still wearing his uniform.
In short order, Hubble met the Mount Wilson staff, two of whom would exert tremendous influence on him. One became an invaluable collaborator, the other had personal issues with Hubble (and vice versa) but still assisted his efforts greatly. Let's take the collaborator first.
MILTON HUMASON (1891–1972)
Milt Humason (1891–1972). AIP Emilio Segre Visual Archives, Brittle Books Collection.
Born in Dodge City, Minnesota, Milt (as he was known) didn't progress in school past eighth grade. After a summer camping experience on Mount Wilson, he fell in love with the mountain and convinced his parents to let him stay there for a year. He never returned to school in Minnesota. Milt became a mule driver and hauled materials up Mount Wilson for the observatory. After taking a year off to be a ranch hand, Milt returned to Mount Wilson as a night watchman. Thanks to solar observer Seth Nicholson's instruction, Humason learned how to use the equipment and some mathematics. From there, Humason became a night assistant, helping astronomers. His patience and technical skills with the instruments impressed everyone. In 1919, Hale appointed Humason to the scientific staff as an assistant astronomer. Shortly after his appointment, he met Hubble. Years later, Humason wrote about that first meeting, “‘If this is a sample of poor seeing conditions,’ Hubble said, ‘I shall always be able to get usable photographs with the Mount Wilson instruments.’ He was sure of himself—of what he wanted to do, and how to do it.”9 The other night assistants were also appreciative of Hubble's direct approach. In Humason's words, “You knew where you stood with him.”10 Humason learned about Doppler shifts from Slipher and developed his own techniques to make long exposures and measure the velocities of dim nebulae. This took care of one of the variables on Hubble's chart. The other variable, distance, is much more complicated and involves the other Mount Wilson astronomer, with whom there were issues.
HARLOW SHAPLEY (1885–1972)
Harlow Shapley (1885–1972). From Wikimedia Commons, user Doctree.
Harlow Shapley was born on a farm in Nashville, Missouri. After dropping out of school in fifth grade and receiving home schooling, he became a crime reporter for a local newspaper. He then completed a six-year high school equivalency program in two years, he graduated as valedictorian in a class of three, and went to the University of Missouri to study journalism at age twenty-two. The School of Journalism opening was postponed for a year, and Shapley decided to study the first course he came across in the college catalog. That was archaeology, but Shapley said he couldn't pronounce it, so he settled for the next course, astronomy. After graduation, Shapley was awarded a fellowship to Princeton University, where he earned his PhD studying under Henry Norris Russell. With his brand-new degree, Shapley was hired by Hale and arrived at Mount Wilson in 1914. Shapley used the sixty-inch telescope to study globular clusters (roughly spherical clusters of stars). After Hubble arrived in 1919, both Shapley and Hubble shared the same equipment, but their personalities clashed. Both were Missourians by birth, but that was about all they had in common. Shapley was a pacifist and more of a down-home country boy, with good social skills and a bold manner. The assistants all addressed him as “Doctor.” Hubble was almost a polar opposite. His military background was obvious, his British accent and dress were pronounced, and his reports were always conservative in tone. Hubble was a bit standoffish and was called “Major.” Privately, Shapley sometimes referred to Hubble as “rubble,” and said “he was a Rhodes scholar and he didn't live it down.”11
As it turned out, they weren't Mount Wilson colleagues for long, but their professional accomplishments were deeply intertwined. Understanding this development and its impact on Hubble's major work will require us to start a bit further back and meet some interesting characters.
HENRY DRAPER (1837–1882) AND MARY ANNA PALMER DRAPER (1839–1914)
Henry Draper (1837–1882). From Wikimedia Commons, user Jbarta.
Mary Anna Palmer Draper (1839–1914). Courtesy of Special Collections, University Library, University of California Santa Cruz, Lick Observatory Records.
Henry Draper was the son of John William Draper, famous for taking the first photograph of the moon. Henry graduated from New York University (NYU) at age twenty, then indulged his fascination with astronomy by traveling to Ireland to see the largest telescope in use at that time. After becoming a doctor, a professor, and a dean at NYU, Draper took photographs of astronomical objects and their spectra to continue his hobby.
In 1867, Draper married Mary Anna Palmer, a wealthy socialite. She embraced his hobby enthusiastically by working as his lab assistant. Unfortunately, Draper died at age forty-five of double pleurisy. His wife carried on his work by donating to the Harvard College Observatory to compile a star catalog in her husband's honor. Currently, the Henry Draper Catalogue contains the spectra of more than a quarter million stars, each classified with an HD number. How did the Henry Draper Catalogue get so many stars? It wasn't easy.
THE HARVARD COLLEGE OBSERVATORY
Edward Charles Pickering (1846–1919) was a physicist who was appointed director of the Harvard College Observatory in 1877 to the surprise of many observers. Astronomically, Pickering had no observational experience, but he represented “new astronomy” in that the methods of physics were now being used to investigate stellar structure and evolution. The observatory used “dry plate” photography and an invention of Pickering's own, a meridian photometer, which spread out the spectrum of stars using a calcite prism. Dry plate photography preserves the images on easily viewed and stored glass plates. Harvard also maintained an observatory at Arequipa, Peru, where they observed stars and galaxies such as the Large and Small Magellanic Clouds, visible from the Southern Hemisphere. As the glass photographic plates began to pile up, Pickering started to wonder about his staff's competence to handle this large amount of information. In exasperation, he told one assistant that his housekeeper could do better work. So Pickering fired the assistant and hired his housekeeper, Williamina Fleming. This proved to be a master stroke. Not only was Fleming better, but Pickering only paid her twenty-five cents per hour—comparable to modern minimum wage. The smaller salaries of the women “computers” (they made calculations by hand) made Anna Mary Palmer Draper's money go much further, so Pickering hired women, more than eighty, eventually. They were known as “Pickering's Harem” and proved extremely adept at the required calculations, classifications, and cataloging.
Many of the women on Pickering's staff went on to careers in astronomy and advanced the cause of women in science. That would be an entertaining story in itself, but the consequences are even more far-reaching. One of Pickering's “computers” in particular made a giant impact on astronomy in general, handing Hubble a tool he desperately needed for his major work. Her name was Henrietta Swan Leavitt (1868–1921).
Edward Charles Pickering (1846–1919) and his staff, called his “harem.” From Wikimedia Commons, user MarmadukePercy.
Leavitt discovered astronomy in her senior year at the Society for Collegiate Instruction of Women, later called Radcliffe College. After remaining in college one more year to study astronomy, Leavitt traveled widely in the United States and Europe, and progressively lost her hearing. Several years later, she volunteered to work at Harvard, and proved to be such a keen observer that she was given the position of chief of the photographic photometry department and was assigned the most difficult task of analyzing variable stars. These were referred to as Cepheid variables, since the first one was found in the constellation Cepheus. She analyzed the Magellanic Clouds (neighbor galaxies of the Milky Way visible from the Southern Hemisphere) and found 1,777 new variable stars. By comparing different photographs of the same star, Leavitt was able to establish that the periodicity of variation (from bright to dim and back again) was related directly to the luminosity (brightness) of the star. This period-luminosity relation was expressed mathematically by Ejnar Hertzsprung and extended astronomy's grip on a perennial problem: distance.
Henrietta Swan Leavitt (1868–1921). From Wikimedia Commons, user Ogrebot.
ASTRONOMY'S DIRTY LITTLE SECRET: HOW FAR AWAY IS THAT STAR?
Seeing a star, whether with naked eyes or through a telescope, is a good start, but the star's distance from us is another matter. As we look at stars overhead, our usual sense of depth perception fails us. All stars appear to be located the same distance away—far. Because our two eyes look at an object from slightly different positions, each eye sights along its own angle. This phenomenon is called parallax and is used by surveyors to make accurate distance determinations. Because of the small separation between our eyes, they cannot be used to judge long distances very accurately.
Astronomy's simplest technique for determining distances to celestial objects is based on parallax, but it uses a much longer baseline than the distance between our eyes. If the same star is observed at the beginning and end of a six-month interval, it is seen at two different angles (just as our eyes see a distant object from two different perspectives). Measuring the difference in angle and knowing that the baseline of a triangle is the diameter of Earth's orbit enables the distance to the star to be calculated using trigonometry. This was first accomplished by Friedrich Bessel in 1838, when he measured the distance to the star named 61 Cygni.
There are more than three hundred stars within thirty light-years (the distance light travels in one year, almost six trillion miles) of Earth, so we can obtain the distances to these closest neighbors by parallax. As you might expect, other astronomical distances are so large they need an expanded scale. Other galaxies are found at distances of thousands of light-years, millions of light-years, or even farther. However, stars beyond about a hundred light-years are so far away that our telescopes are unable to measure their angles accurately enough to determine their distance.
This is where Leavitt's period-luminosity comes into focus. In 1913, Danish astronomer Ejnar Hertzsprung used this relationship in a very clever way. Measuring the period (time from one bright flash to the next) allowed him to determine the star's intrinsic luminosity, then the measured apparent luminosity allowed the distance to be determined using the inverse square law. (For example, starting with two equally bright stars, the one twice as far away would appear only one-fourth as bright.) This technique was then used by other astronomers to measure more stellar distances, as long as they could spot the particular kind of star needed—a Cepheid variable.
Harlow Shapley made excellent use of the new measuring tool almost immediately. He studied globular clusters (a spherical collection of stars, similar in shape to a globe) and found enough Cepheid variables within them to determine their distances. (The stars he thought were Cepheid variables were not classic ones and had a slightly different period-luminosity relation, which caused Shapley to overestimate the size of the galaxy.)
This brings up a sore point in astronomical history. In the early 1900s, there were real live questions in astronomy. What is the size of the Milky Way Galaxy; how big is the universe; what are those pesky nebulae, and how far away are they?
We need some history here to put these questions into perspective. The term galaxy is derived from the Greek term galaxias kyklos, which translates to “milky circle” (Milky Way). Swedish philosopher Emanuel Swedenborg (1688–1772) theorized that all stars formed one large group, with the solar system just one part. In Swedenborg's book Principia Rerum Naturalium (1734) he proposed that our solar system of sun and planets was formed from a rapidly rotating nebula. The source of Swedenborg's information wasn't any scientific observation, although he did study science. He got his information from a séance that allegedly included visitors from heaven. Later visions encouraged Swedenborg to reveal theological information, and a religion eventually sprang up from his teachings.
The galaxy story continues with an Englishman, Thomas Wright (1711–1786) of Durham, who built scientific instruments and model solar systems that he sold to the nobility. In his 1750 book An Original Theory or New Hypothesis of the Universe, Wright proposed that stars in the Milky Way are distributed in a kind of shell or disk. He declared, “I can never look upon the stars without wondering why the whole world does not become astronomers.”12 As a scientific instrument maker, he undoubtedly had access to telescopes. However, Wright published no astronomical observations. His book also dealt with religious matters such as the physical location of God's throne.
Stranger still, a review of Wright's book in a Hamburg journal caught the eye of the brilliant philosopher Immanuel Kant (1724–1804). Although Kant misread the account of Wright's work, he proceeded to extend it in a constructive direction. In 1755, Kant proposed that the Milky Way was a lens-shaped disk of stars, rotating about its center. Further, he suggested that the fuzzy patches of light referred to as nebulae were actually systems of stars similar to the Milky Way but very far away. He referred to them as “Island Universes.”
So, the beginnings of astronomy's analysis of galaxies came from a philosopher, a theologically oriented instrument maker, and another philosopher. There were other ideas later, but let's cut to the chase. In the 1900s, observational astronomers had generated huge amounts of information but needed some theoretical framework to give it order. Harlow Shapley stood ready to take on that task, as his globular cluster distance measurements provided him with information that implied a new picture for the galaxy. He plotted the locations of the globular clusters in three dimensions and presumed this defined the outer boundaries of the Milky Way. This was a radical new idea, far different than the more traditional galaxy size.
THE GREAT DEBATE
Heber Curtis (1872–1942). Courtesy of Special Collections, University Library, University of California Santa Cruz, Lick Observatory Records.
The contrast between Shapley's model of the Milky Way and the more conventional one came into sharp focus in 1920 at a meeting of the National Academy of Sciences in Washington, DC. The young Harlow Shapley was invited to give the William Ellery Hale (George's father) Lecture that year. But, rather than a straight presentation, the lecture was set up as a debate. Shapley was joined by the Lick Observatory's Heber D. Curtis (1872–1942), who had just completed a survey of spiral nebulae. The title of their debate was “The Scale of the Universe.”
Curtis argued the standard view of the time: the Milky Way was lens-shaped, about thirty thousand light-years in diameter, and the sun is located near its center. In his concluding remarks, Curtis departed from the confines of the stated topic and ventured that spiral nebulae are quite distant and constitute separate galaxies. Curtis had no evidence to support this conjecture, but he challenged Shapley to give his opinion.
Shapley gave a much less technical talk than Curtis. His audacious estimate of the Milky Way size was three hundred light-years in diameter, with our sun far from the center. Although Shapley was not prepared for the spiral nebulae issue, he believed they were small gas clouds still within the large confines of the Milky Way Galaxy. He cited recent observations of a Mount Wilson colleague (and personal friend), Adriaan van Maanen (1884–1946). Van Maanen had reported that he measured rotational speeds of the Pinwheel Nebula that would lead to star velocities greater than the speed of light if the nebula was located outside the galaxy. Curtis dismissed van Maanen's work as being unsubstantiated. Later, van Maanen's reports turned out to be faulty.
While the debate had no clear winner and wasn't even well-attended, the idea of a larger Milky Way with the earth far from its center seemed to catch the public's attention. Back at Mount Wilson, Shapley's colleague Edwin Hubble made no secret of his sympathies for Curtis, but it was clear that more information was needed.
There was a hidden agenda to the debate, however. The previous year, Harvard College Observatory's director Edward Charles Pickering had died. Pickering had built Harvard to such prominence that his replacement would have a plum job. Shapley wanted it. Not only did Harvard have excellent staff and equipment, it also had access to Southern Hemisphere observations, so Shapley could explore the Large and Small Magellanic Clouds. After some negotiations, Shapley was offered the directorship by Harvard president Abbott Lawrence Lowell (Percival Lowell's brother), and he took it, effective April 1921. This left Hubble at Mount Wilson with more hundred-inch telescope time, and Shapley filling the job he dreamed about. There had been rumors on Mount Wilson about Shapley's leaving, and they were right. A spot of luck, Hubble might say.
With Shapley no longer competing for telescope time, Hubble went to work with renewed vigor, training the hundred-inch on his favorite targets: nebulae. Within a year, Hubble had surveyed all the nebulae he could find and proposed the beginnings of a classification scheme for nebulae. Later additions and refinements to this scheme produced much controversy, but a far more sweeping result was on the horizon. While Hubble continued to pile up data to refine his scheme, he noticed something extremely unexpected. In October 1923, he found a variable star in M31, the Andromeda Nebula. At first, he thought he had sighted a nova, but subsequent observations showed it to be a Cepheid variable. The hundred-inch had presented him with a means of finding the distance to the Andromeda Nebula. Using Leavitt's period-luminosity relation in the same fashion as Shapley had for globular clusters, Hubble found the distance: almost a million light-years. This settled the debate question about nebulae, and not in Shapley's favor. But Hubble, being the careful fellow that he was, needed more data. By February 1924, Hubble had enough to write to Shapley. “You will be interested to hear that I have found a Cepheid variable in the Andromeda Nebula (M31). I have a feeling that more variables will be found by careful examinations of long exposures. Altogether next season should be a merry one and will be met with due form and ceremony.”13 Cecilia Payne, soon to be Harvard Observatory's first PhD in astronomy, was in Shapley's office when the missive arrived. He remarked to her, “Here is the letter that destroyed my universe.”14 Indeed, this established nebulae as galaxies in their own right, but Hubble never stopped calling them nebulae.
Bonus Material: Hubble/Shapley Internet interview. See To Dig Deeper for details.
By the 1920s, Hubble had accomplished quite a lot. He held athletic records in Illinois, he had been a Rhodes Scholar, he had served in World War I and achieved the rank of major, he had earned a PhD in astronomy, and he had a job as an astronomer at the largest telescope in the world. He had passed his thirtieth birthday and was looked at as an extremely eligible bachelor. That was just about to change.
Grace Burke Leib visited Mount Wilson with friends in 1920 and met Hubble purely by accident. She came from a wealthy family. Her father was a vice president of the First National Bank in Los Angeles. Grace majored in English at Stanford University, where she managed to maintain straight As and become Phi Beta Kappa. Six months after graduation, she married Earl Warren Leib, who came from the most prominent family in San Jose. Just a year older than Grace, Earl had graduated from Stanford with a degree in geology and mining. The childless couple lived with her parents, and he worked in the mining industry.
In 1921, Leib traveled to Amador County, southeast of San Francisco, to obtain mine samples for his employer, the Southern Pacific Company. He climbed down the ladder to the mine shaft, and about halfway down became overcome by gas and fell to his death. Hubble and Grace renewed acquaintances a year after her husband's death, carried on a discreet courtship, and were married in 1924. In recognition of his meager salary and his new wife's background, Hubble supposedly offered to give up astronomy to become an attorney, but Grace would have none of it. A three-month honeymoon took them to New York, Boston, England, France, and Italy on a trip they found delightful. Along the way, the newlywed Hubbles had picked up several ideas for a home, and not long after their return, they found the ideal setting: San Marino's Woodstock Road. Not far from Mount Wilson, the site had spectacular views, and was situated on a geologic fault line, a fact that Hubble loved to point out to visitors.
Grace Burke Leib Hubble (1889–1981) and Edwin Hubble. Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California.
Upon returning to Mount Wilson, Hubble continued to work on his nebulae classification scheme and became embroiled in a controversy with Swedish astronomer Knut Lundmark (1889–1958). During the same time, V. M. Slipher was reaching the limitations of his equipment for measuring radial velocities of nebulae—his telescope was too small. As he tried to measure dimmer nebulae, Slipher needed longer and longer exposure times because his twenty-four-inch telescope just didn't capture enough light. Hubble had less of a problem because of Mount Wilson's hundred-inch telescope's light-gathering power. Besides, Hubble found Cepheid variables in nebulae, so the distance-measuring problem was solved using the work of Leavitt, Hertzsprung, and Shapley. Hubble set Milt Humason to work on the velocities. Humason started by duplicating Slipher's work, confirming all the earlier red shifts. But, as they observed nebulae much dimmer than those used by Slipher, they started experiencing extremely long exposure times. This discouraged Humason, but Hale came to the rescue by obtaining a faster spectrograph and an improved camera. Exposure times decreased from several days to hours, and they began to roll. After many long, cold nights of observing, taking photographs, developing them, and interpreting results, Hubble finally had enough data in March 1929 to publish “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae” in the Proceedings of the National Academy of Sciences.
Hubble wrote Shapley that he had held the paper for more than a year, wanting more data. Two years later, he had the additional data, and published “The Velocity-Distance Relation among Extra-Galactic Nebulae,” coauthored with Milt Humason, which included measurements of another fifty nebulae. Ever the cautious skeptic, Hubble handled the theoretical implications with “long tongs.” “The present contribution concerns a correlation of empirical data of observation. The writers are constrained to describe the ‘apparent velocity-displacements’ without venturing on the interpretation and its cosmologic significance.”15
Strictly speaking, this relationship does apply only to the galaxies Hubble measured. However, when generalized, it implied something remarkable: The Universe as a whole is expanding.
To see how this happens, consider a simple analogy. Suppose there is a race, the Cosmic Marathon. When the race begins, a few runners take off at 4 miles per hour, some at 3 miles per hour, and others at 2 miles per hour.
One hour into the race, the 4-mph group would have covered 4 miles, the 3-mph group 3 miles and the 2-ph group 2 miles, producing a graph just like the one generated by Hubble. Note that from any runner's perspective, it seems that all others, both the ones ahead and the ones behind, are moving away. That is the point of the Hubble graph: the farther away galaxies move faster; that's how they got to be farther away.
The linear relationship between galaxy recession speed and distance is now called Hubble's law in his honor. Although the distances Hubble determined have been corrected somewhat by modern measurements, Hubble's fundamental results remain valid. The universe consists of galaxies of stars and is huge and expanding.
Courtesy of NASA.
Einstein, Hubble, and others at Mount Wilson, 1931. Image courtesy of the Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California.
Theoreticians had a field day because there was physical evidence for the ideas of theoreticians Georges LeMaître, Alexander Friedmann, Willem de Sitter, and others. But the happiest theoretician was one who was able to remove a term from his theory: Albert Einstein (see chapters 9 and 10). Now that the necessity for a static universe was removed, the need for Einstein's “cosmological constant” vanished.
In 1931, Einstein came to California. He was scheduled to divide his time between Mount Wilson and Caltech. Sparing no expense, the usually frugal director Walter Adams purchased a “big Pierce Arrow touring car” to convey Einstein up the mountain. Einstein had no experience with equipment of the type on Mount Wilson, and he climbed all over the framework of the hundred-inch telescope, chattering about many details about various instruments—Einstein had done his homework. Elsa Einstein, watching from a safe distance, was told that the giant telescope enabled astronomers to determine the universe's structure. She replied “Well, well, my husband does that on the back of an old envelope.”16
While he was visiting Mount Wilson, Einstein announced the removal from his equations of the cosmological constant, which he regarded as a blunder. This catapulted Hubble further into the limelight. The Springfield Missouri Daily News read, “Youth Who Left Ozark Mountains to Study Stars Causes Einstein to Change His Mind.”
The Einsteins soon scheduled a return visit to Pasadena, and arrived there in November 1931. Grace Hubble served as an unofficial hostess and drove Einstein to his commitments. Although he was mostly silent, he once told her, “Your husband's work is beautiful—and he has a beautiful mind.”17 Interestingly, Hubble's attitude about religion was quite similar to Einstein's. When asked about his beliefs by a depressed friend, Hubble said, “The whole thing is so much bigger than I am, and I can't understand it, so I just trust myself to it: and forget about it.”18
Thanks to the Einstein and Hubble publicity, Mount Wilson turned into a tourist destination, and it became harder to work there. The Hubbles enjoyed the publicity and entertained many Hollywood stars, including Anita Loos, Harpo Marx, Charlie Chaplin, Paulette Goddard, Lillian Gish, Helen Hayes, Frank Capra, Jane Wyatt, George Jessel, Clifford Odets, Leslie Howard, William Randolph Hearst, and Clare Boothe Luce. Hubble became involved in the design of the two-hundred-inch telescope on Mount Palomar and was granted first use in 1949. His health deteriorated, and he died in 1953.
In 1990, the Hubble Space Telescope was launched, with a primary mirror diameter of ninety-three inches, almost as large as the Mount Wilson telescope of one hundred inches. Because of its position in orbit, there was no atmospheric interference and day/night problems were no longer an issue. The HST offered a phenomenal window into the universe.
Horsehead Nebula. NASA, ESA, and the Hubble Heritage Team (STScI/AURA).
The James Webb Telescope, scheduled for launch in 2018, features a 242-inch mirror and will allow observation of some of the most distant objects in the universe.
Now that we've seen how science can reveal fascinating things about the world of the very large, the next chapter will explore the incredibly small—but with calamitous technological as well as ethical consequences.