The Stardust Revolution

by Jacob Berkowitz

  What consumed Hale's deep passion and fed his workaholism weren't just the stars but also the deep belief that in them we'd learn something essential about ourselves. Hale founded the Carnegie Observatories in Pasadena, just ten miles from the mountain's base, as the location of offices for the Mount Wilson astronomers. In his office there, Hale's personal library, which included original works by both Galileo and Copernicus, also included a thumb-worn fifth-edition copy of Charles Darwin's On the Origin of Species. For Hale, evolutionary theory was as much a commentary on the origins of stars as of species. “It is not too much to say that the attitude of scientific investigators toward research has undergone a radical change since the publication of Origin of Species,” he wrote in his 1908 book The Study of Stellar Evolution. “This is true not only of biological research, but to some degree in the physical sciences. Investigators who were formerly content to study isolated phenomena, with little regard to their larger relationships, have been led to take a wider view.”

  Hale believed that the key to this wider view of the cosmos began not with peering at distant stars but in studying just a single nearby one: the Sun. “We are now in a position to regard the study of evolution as that of a single great problem, beginning with the origin of the stars in the nebulae and culminating in those difficult and complex sciences that endeavor to account, not merely for the phenomena of life, but for the laws which control a society composed of human beings. Any such consideration of all natural phenomena as elements in a single problem must begin with a study of the Sun, the only star lying near enough the Earth to permit detailed investigation.”

  The idea of doing astronomy in daylight is counterintuitive until we remember that the Sun is in fact a star and not so different from the approximately two hundred billion other stars in the Milky Way or the uncountable trillions of stars in the universe. It was this insight that made Hale not an astronomer but a solar observer. From nineteenth-century discoveries, Hale knew that the study of sunlight could provide powerful clues to unlock the secrets of the night sky, a new field of study he called astrophysics. His observatories would be laboratories, places where astronomy met terrestrial physics; where, through an understanding of what we see, measure, and describe on Earth, we can fathom the stars and in turn learn about ourselves. With astrophysics, astronomers could move beyond understanding where the stars are to knowing what they are. The key to this understanding lay in the Sun.

  In 1903, having convinced Andrew Carnegie and his Carnegie Institution to pay the tab, Hale founded the Mount Wilson Solar Observatory. He chose this Southern Californian summit for its good “seeing”—the air masses over the peak were unusually quiescent—Hale arranged for Mount Wilson's first telescope, its sixty-foot solar telescope to be hauled up to the peak, mules carrying the telescope, every steel girder, and eventually the finely polished mirror, up from the dry, sage-scented canyons below, along precipitous and narrow cut-back trails today walked by weekend hikers packing electrolyte-balanced energy drinks. The solar observatory was completed in 1907, and a year later, Hale used it to become the first person to see that sunspots contain magnetic fields. Each spot is actually a married pair—a negative and a positive pole. It was a monumental insight, the first observation of magnetism beyond the Earth, adding one more astrophysical link between the heavens and the Earth. In order to tease more information out of sunspots, however, Hale needed a bigger telescope. Thus was born the 150-Foot Solar Tower, completed in 1912.

  Standing in Hale's solar observatory while the repetitive whir of the magnetograph scans across the disk of the Sun, automatically measuring its motion and magnetic fields, I ask Padilla what he likes most about his job. “Every day I get to look at a star,” he says with an impish grin, echoing Hale's vision. “It's our closest star. By looking at the Sun we're seeing how a star works.” It's a line he's delivered to thousands of visitors, but it's no less powerful for that: strange as it is on one level, it's easy to forget. On clear nights, if we're outside the shroud of city lights, we see stars as twinkling points of light—deeply distant, cold, and mysterious. By midday, given that the stars now seem as though they have never been in the bright-blue sky, it might be difficult to believe that the intense, fiery, blinding Sun is just like those points of midnight light.

  I've come here to see the solar spectrum. We see this spectrum in a dilute form when droplets of water in the atmosphere split sunlight to create a rainbow—dividing sunlight into its component parts from red through yellow to violet. But, using a spectroscope, the equivalent of a high-tech prism, the solar observatory dissects sunlight to create an enormously high-resolution spectrum, revealing otherwise invisible details of the stellar rainbow. Padilla adjusts “the periscope,” a viewing tube for looking at the spectrum. I glance toward the wall at a picture of Einstein bent over, his eye on the periscope, and Hale bent over Einstein's shoulder, as if asking, Can you see them?

  “There, take a look,” says Padilla. I look through the periscope and gently move the view across the solar spectrum. There they are: the Fraunhofer lines, an intermittent series of seemingly randomly spaced thin, dark lines across the pale-green section of the spectrum Padilla has focused on. Not fuzzy or flickering, these dark lines are ruler-straight, evoking the dark lines drawn by a government censor to redact a document. Directly in front, I see a pair of lines, one a little thicker than the other; to the left is a thin, lighter line. Looking up, I see that these lines correspond exactly with the photograph of the Fraunhofer lines that Padilla uses as a benchmark to calibrate his observations. These particular lines are from atoms of ionized iron dancing in the Sun's atmosphere, absorbing photons of sunlight produced in the Sun's core, and thus acting as tiny shields revealing the Sun's composition. These Fraunhofer lines are the reason that Hale built this observatory. After the telescope itself, these lines are the cornerstone to our understanding of the cosmos. They were the great astronomical riddle of the first half of the nineteenth century. The serendipitous solution to that riddle set in motion a revolution: the Stardust Revolution.

  OUT OF MYSTERY

  Why did Hale so fervently think that studying the Sun would reveal the hidden nature of all stars? To answer this question, we have to go back to a book published in installments between 1830 and 1842: Auguste Comte's six-volume treatise The Course in Positive Philosophy.

  Comte, one of the great nineteenth-century philosophers, was an eminently reasonable man. In fact, he was one of the most rational men of the century. Born in 1798, a child of the aftermath of the French Revolution, Comte expounded that a deliberate mixture of love and reason could form the basis for a new, harmonious social order, one that spurned the guillotine and rejected blind obedience to Church and monarch. Comte wrote prolifically, and his ideas were heard around the world. Brazil's fathers of independence were guided by his famous creed “Love as a principle, the order as a foundation, and progress as a goal,” weaving a shortened version into Brazil's flag as “Ordem e Progresso.” Comte's fame waned in the past century, though the intellectual fields he founded would impress anyone. In his application of science and reason to human affairs, Comte inspired sociology, and his thinking about the sciences made him the first modern philosopher of science.

  Comte wasn't merely interested in what we know but also in thinking about how we know things and, ultimately, what is knowable. In The Course in Positive Philosophy, he covered all the sciences of his day in incredible detail, from astronomy to biology. When this French philosopher looked at the stars in the night sky over Paris, he was certain of one thing: we would never know their deep nature. “Men will never encompass in their conceptions the whole of the stars,” he reflected. “We can never know anything of their chemical or mineralogical structure.”

  Comte wasn't simply a naysayer. His statement came at a historic tipping point—the birth of modern science. He wanted to set a new standard for describing the world we see and our expectations of what we might come to understand. His point was
n't that the stars are innately mysterious or divine and therefore beyond human understanding. Comte's argument was based on deliberate reasoning. He pointed out that, then as now, we have three modes of scientific exploration: direct observation, experimentation, and comparison of similar systems in order to see commonalities and differences.

  As for the stars and planets, he reasoned, “Experiment is, of course, impossible.” You couldn't sample a star and bring a fiery chunk into a laboratory to study it under a microscope or subject it to the growing wonders of nineteenth-century chemistry and physics. As for comparison, he reasoned, it “could take place only if we were familiar with an abundance of solar systems, which is equally out of the question.” Thus, he concluded, all that would ever be possible was observation. All you get from a star is a twinkling speck of light. Pretty, but not the stuff of science. For all the grandeur of the night sky, Comte believed that astronomy—limited as it was by the observation of faint light from distant bodies—was forever restricted to the domain of the mathematician, “measuring angles and computing times of the heavenly bodies.” In the vernacular, astronomy was a dead-end discipline, but Comte reasoned that “if the knowledge of the starry universe is forbidden to us, it is clear that it is of no real consequence to us, except as a gratification of our curiosity.”

  He was far from alone in his assessment. Astronomers of the day could observe the motions of stars and planets but could not figure out what they were made of. Yet even as Comte was writing, the first cracks were appearing in the wall of the “impossible” nature of the stars. Within several years of Comte's death in 1857, scientists would proclaim that, far from being unknowable objects, it was indeed as if you could hold a star in your hands and tease secrets from it, a revelation that came not from looking at a shining star but at the light of a little flame.

  BUNSEN'S BURNINGS

  If there's just one thing generations of students remember from high school chemistry, it's Robert Bunsen's last name, immortalized in the eponymous small, metallic burner that's emblematic of chemistry class. It may come as a surprise to many familiar with Bunsen as a chemist that when he died at the age of eighty-eight on August 16, 1899, his obituary appeared not only in chemistry journals but in the Astrophysical Journal. Listing Professor Bunsen's many scientific accomplishments as one of the great chemists of the nineteenth century, the obituary writer reflected that “the work for which Bunsen will, possibly, be longest remembered is that which he did with Kirchhoff in establishing the science of spectrum analysis.” Ironically, Bunsen is remembered for the burner he neither solely invented nor claimed as his own. Yet his deepest contribution to science is a largely unknown story. It was what he did with his burner—and the purpose for which he finessed it—that makes his the first great story of the Stardust Revolution.

  Robert Bunsen had an early penchant for studying things that burned or blew up in the most violent ways. By all accounts, he was a gracious friend and colleague, but when it came to experiments, he loved to live on the edge. Bunsen's fame came not from great theoretical insight but from the fact that he was a persistent, deeply creative experimenter and laboratory innovator. He sought new ways to tackle vexing problems, even at great personal risk. In 1847, Bunsen traveled to Iceland, where he became fascinated with the island's angry geyser eruptions of searing hot water and steam. To understand their cause, he positioned himself on the lips of geysers and lowered thermometers into the geyser tube immediately before an eruption. In the seemingly safer confines of the laboratory, he discovered the first member of a series of arsenic-based compounds called cacodyls, named from the Greek term meaning “evil-smelling matter.” To appreciate just what an accomplishment this was by nineteenth-century chemistry standards, when the idea of a fume hood was science fiction, you need to consider the substance's particular qualities. Cacodyl's smell resembles that of garlic, according to those who have smelled it—and lived to tell the tale, for it's also extremely toxic. Bunsen found that a vaporized speck of the stuff, today known as tetramethyldiarsine, was enough to kill a frog. Additionally, it spontaneously combusts in air. On one fateful occasion, a cacodyl explosion permanently blinded Bunsen's right eye and left him on the verge of death for several days from arsenic poisoning. Yet he seemed to revel in the substance's extreme noxiousness, noting that not only did it smell repulsive but that exposure to its vapors caused nausea, a sense of suffocation, and an almost unendurable, long-lasting irritation of the nasal mucous membranes.

  Bunsen's discovery of cacodyl, exciting to chemists as the first organic compound containing a metal, was part of a larger mission. Throughout the 1800s, chemists, including Bunsen, worked painstakingly to isolate and thus discover new compounds, particularly new elements. The challenge was how to chemically and physically separate elements and then distinguish a small sample of one silvery metal, or one grayish crystalline powder, from another. This is where Bunsen's burner came in. Nineteenth-century chemists knew that when different pure elements were burned in a flame, they produced distinctive colored flames. Burning sodium produced an orange burst of flame; copper, blue; and zinc, bluish-green. It's these burning elements that produce the fantastic, flaring colors of fireworks. Bunsen reasoned that it would be possible to isolate and discover unknown elements based on their flame color. To do this, he wanted a burner that produced a hot flame but very little light, so that the flame's light wouldn't compete with the light emitted by the chemicals he was burning. Working with his lab technician, Bunsen finessed existing designs of coal gas burners, adding the critical air baffle at the bottom of the combustion tube to create a burner whose flame could be rendered almost invisible. It's this characteristic of the Bunsen burner that makes fine-tuning the flame such an alluring experience—getting the near-invisible flame. Yet, even with a colorless flame, Bunsen found that many elements’ flame colors are too similar, as shades of blue-green or red, to be of scientific value. Then the great chemist had an idea. He would hold colored pieces of glass in front of his eye to look for small differences that would let him distinguish between elements. A blue lens would absorb the blue from the glowing element, leaving visible any other perhaps identifiable colors.

  In the fall of 1859, while Europe's natural history community was abuzz with the controversy created by Darwin's On the Origin of Species, Bunsen, in his stone-walled lab in Heidelberg, set to work with his burner and pieces of colored glass, identifying the colors of light emitted by different chemical “species” (as elements were sometimes called) when they were heated in the burner's flame. This is how Bunsen's friend and colleague physicist Gustav Kirchhoff found Bunsen when he rolled into the chemist's lab one day in the summer of that year. Kirchhoff, using a wheelchair as a result of a childhood accident, had become one of Europe's greatest physicists, accomplishing fundamental work in electricity and later developing the concept of blackbody radiation—the characteristic emission of different wavelengths of light by an object at a specific temperature. The two scientists had met at the University of Breslau, and Bunsen had been instrumental in getting Kirchhoff a position at Heidelberg. It would later be said that Kirchhoff was Bunsen's greatest discovery.

  Used to comfortably brainstorming experimental ideas, Kirchhoff immediately pointed out that there was a far easier and more precise way to study an element's emitted light—use a prism to break the light into a spectrum. The idea was far from new, but even in the mid-nineteenth century it held an aspect of the surreal from the time when Sir Isaac Newton, three centuries earlier, had conducted the first modern scientific light experiments. In Newton's day, spectrum was synonymous with specter—a phantom or apparition. This etymology gives a sense of Newton's awe when, having bought a prism at a local market, he carefully drew closed the curtains in a room until only a single shaft of sunlight pierced the room's gloom. Then the über-savant placed his prism in the light's path. It was a light miracle. On the side of the prism closest to the curtain, a shaft of white light entered it, but when the light
exited the prism, it projected on the far wall a rainbow of color.

  Many others had already observed that white light actually consisted of a rainbow of colors. What set Newton apart was that he didn't just see the rainbow for itself but that he understood that sunlight held a deeper story, one that could be teased apart by separating the light. He showed that, by using a second prism, the rainbow of light could be reconstituted into white light and that the rainbow effect was created by the different colors of light being refracted, or bent, in different amounts by the prism, thus adding an all-important level of quantification. Newton explained all this in 1672, in the first paper he sent to the Royal Society, in which he used the word spectrum in its modern sense. He'd turned a ghost into a matter of science.