The Moon and Sun have not always been places. For the majority of the past two millennia, the prevailing view was that stars and planets were mere points of light and the Moon and Sun ethereal spheres. These spheres were eternally bright and moved each day in perfect circles above the corruptible Earth, where everything falls and decays. In matter and motion, there was nothing similar between Heaven and Earth. In the world before Copernicus, the Earth was the only world. This separation of Heaven from Earth and gods from man is attributable to Aristotle more than 2,300 years ago. It’s an idea that makes a certain amount of sense: We see rocks tumble, yet the Sun rises. Wood burns like the Sun, yet the Sun seemingly burns forever. In fact, according to Greek mythology, we humans only have fire on Earth to fuel our civilization by the gift of Prometheus, who stole it from the heavens.
From myth to modern astrophysics, the Sun is the unifying thread in the story of our position and origin in the Cosmos. Understanding its fire has revealed that the heavens, the Earth, and we ourselves are all subject to the same forces and composed of the same substances. This story, that we are the heavens made manifest, is one we know from eclipses.
It is a story that begins with the Moon. Though the rest of the sky is full of pinpoint stars and a (blindingly) featureless Sun, the Moon has obvious features. All over the world, people have seen these dark markings, identifying them as depicting a man, a woman, or even a rabbit. Yet up until only the past four hundred years, had you asked a learned philosopher about the nature of the Moon, you would have been told that it was a perfectly smooth, unblemished sphere. Philosophers posited that the Moon was smooth but composed of a translucent crystal with pockets of different densities. Others believed that these markings were simply the mirror-like reflection of the imperfect Earth. Some argued that the Moon wasn’t solid at all, but rather a cloud of spherical vapor through which light more or less easily passed.
The unifying theme was that the Moon, as a celestial orb, must remain a perfect sphere that shared no common feature with a physical place like the corruptible Earth. Unfortunately, what we could see with our eyes could only tell us so much. That changed in November 1609 when Galileo Galilei pointed a telescope at the sky and beheld the Moon with a magnification beyond that of our own eyes. What he saw was a complex array of light and dark features even smaller and more intricate than the face we see in the Moon each month. But what could they be?aa From the time of Leonardo da Vinci, Italian artists had endeavored to create realistic representations of the natural world in drawing and painting using geometry and perspective. Galileo, raised in the heart of Renaissance Florence, was intimately aware of these techniques, including that of chiaroscuro, the contrasting interplay of light and shadow across solid surfaces. Looking through his eyepiece, he instantly recognized the three-dimensional reality that had been hidden there for so long: “[I] have been led to the conclusion that we certainly see the surface of the Moon to be not smooth, even, and perfectly spherical as the great crowd of philosophers have believed about this and other heavenly bodies, but, on the contrary, to be uneven, rough, and crowded with depressions and bulges . . . like the face of the Earth itself which is marked here and there by chains of mountains and depths of valleys.” Because Galileo does not say what curiosity made him first point his telescope at the Moon, it is impossible to say what he expected to see. As an astronomer who has had the pleasure of using a new telescope with capabilities never before available, I can say that this is the most exciting moment in any scientist’s life. To look with new eyes at worlds never before seen, where every sight is a source of surprise, is science at its most thrilling.
Galileo went further: if the Moon had mountains, then he should be able to measure their height. To understand how this is possible, imagine standing in a meadow before dawn, with mountains behind you to the west. Long before you see the Sun rise, the mountain peaks behind you are lit; the first peaks to be touched are the tallest. Galileo saw the same phenomenon on the Moon. He measured how far into the lunar night a mountain could be and still have its peak lit by the Sun. The farther into night the sunlit peaks appeared, the taller the mountain must be. His eyepiece revealed that they were comparable in height to our own mountains. Eighty years later, when Isaac Newton published his mathematical law of gravity, he proved that the exact same force that caused stones to fall also kept the Moon in orbit around the Earth, as predicted by Kepler’s three laws of orbital motion. The same physical force was therefore at work shaping the landscape both here and in the sky. The Moon was now a place where any scientist or artist could imagine standing and watching the sunrise.
Could we make the same measurements for the Sun? Using a telescope to project an image of the Sun upon a piece of paper, Galileo saw that it had spots. The Sun, like the Earth and the Moon, was blemished.
Galileo and his contemporaries were not the first people ever to see sunspots. On occasion, sunspots can grow to over ten times the size of the Earth (as large as the planet Jupiter). When this happens, they are large enough to be seen without a telescope, especially through thick haze or when the Sun is low on the horizon.bb Chinese records going back to 165 BCE tell of sunspots viewed by the naked eye. The fourteenth-century Indian Kashi Khanda text describes a Sun whose face was covered by dark snakes—almost certainly sunspots—a sight that would have been visible as the morning Sun rose through the mist of the River Ganges.
Due to the blinding light of the Sun’s photosphere (meaning, literally, its surface of light), sunspots are the only feature of the Sun that we can ever see under normal circumstances. But solar eclipses aren’t normal circumstances. As when holding up a hand to block the glare of a street lamp at night, suddenly we see more for having less light to hide what is there. Solar eclipses have been the greatest tool for understanding the geography—or perhaps, the heliography—of the Sun. Before the nineteenth century, eclipses were interesting primarily for what their occurrence and duration revealed about navigation and timekeeping on Earth. In the early 1800s, the English astronomer Francis Baily was more interested in what eclipses revealed about the Sun and Moon themselves. While most astronomers merely observed eclipses that happened to pass over their homes (making drawings later to record what they could remember), Baily was willing to go wherever necessary to see what he could discover and record his findings on the spot as they were happening.
Born in 1774, Baily was the son of an English banker. He was a studious young man and interested in science, but as soon as his mercantile apprenticeship was over, he left London for adventure in the United States. His letters from this time read like a Robert Louis Stevenson novel: a harrowing shipwreck on the high seas, disgust at the slave trade in the West Indies, boating and canoeing down the Ohio and Mississippi Rivers to New Orleans, and then walking back to New York overland through 2,000 miles of Indian-filled wilderness. For a while he thought of staying in America (there was a rumored romance, according to his friends back home), but eventually he returned to England. There he attempted to continue his life of travel by seeking service with the East India Company in Turkey and the Africa Association to explore the far-off Niger River. In the end it came to nothing, and so finally he accepted a position in London as a stockbroker.
Although Baily excelled and wrote revolutionary papers on the mathematics of interest and annuities—the first to do so using algebraic equations and symbols—his interests eventually turned back to science. In 1811, he calculated the date of the first recorded total solar eclipse in the Western world: that of Thales of Miletus (which he concluded occurred on September 30, 610 BCE). Twenty-five years later, in 1836, Baily was president of the Royal Astronomical Society, and his calculations revealed that the Moon’s shadow would sweep across Europe on July 18, 1842. It would be the first total solar eclipse to cross the continent in 118 years, a sight virtually no living European could claim to have yet seen.
Baily had already seen an annular eclipse. In 1836, he had traveled to Scotland with his telescope to observe the event and in the process reported an unusual sight. At the precise moment that the Moon moved fully in front of the Sun, when the thin crescent of light wrapped itself around the Moon to become a ring, a complicated pattern of bright “beads” came into view where the two “horns” of the crescent were about to touch. Baily was not, however, the first to see these “beads.” The Reverend Samuel Williams of Harvard University had seen something similar in 1780 during a total eclipse of the Sun on the coast of Maine. He had traveled there to set up telescopes and chronometers to measure the time and duration of totality. Unfortunately, whether through errors in his maps or his math, Williams’s expedition just barely missed totality’s path by a matter of miles. He got close enough, though, to record the appearance of multiple bright points of sunlight moving along the thin rim of the Moon where at maximum obscuration it skirted the edge of the Sun. Williams’s failure to reach totality meant his observations were not widely read, but some astronomers have suggested that during his time in America, Baily might have become aware of Williams’s description and so made special efforts to see these bright points of light for himself in Scotland.
The phenomena are now called “Baily’s beads.” They form at the first and final moments of totality when sunlight streams through mountains and valleys along the edge of the Moon—the very same ones Galileo first discovered—and they break up the Sun’s light into rays that shimmer in and out of existence until the bright disk finally disappears. Without Galileo’s discovery, there is no explanation for what everyone sees at the moment of totality.
It was the hope of seeing these beads again that most excited Baily about the 1842 total eclipse in Pavia, Italy. Sitting in a high apartment, his eye to his telescope, Baily’s observations convey the excitement in the last final moments as the Sun disappeared behind the Moon:
I was astounded by a tremendous burst of applause from the streets below, and at the same moment was electrified at the sight of one of the most brilliant and splendid phenomena that can well be imagined. For, at that instant the dark body of the moon was suddenly surrounded with a corona, or kind of bright glory, similar in shape and relative magnitude to that which painters draw round the heads of saints. . . .
I had indeed anticipated the appearance of a luminous circle round the moon during the time of total obscurity: but I did not expect, from any of the accounts of preceding eclipses that I had read, to witness so magnificent an exhibition as that which took place.
The Spanish astronomer José Joaquín de Ferrer was the first person to call this radiance the corona, Spanish for “crown,” when he saw it during the total solar eclipse of 1806 from the banks of the Hudson River in upstate New York. Ferrer measured the corona’s extent across the sky and calculated that if there was a lunar atmosphere (which during the eclipse would be illuminated by sunlight the way steam from a cup of coffee might be illuminated by the morning sunlight on Earth), then it must extend 348 miles out into space, 50 times higher than our own. Although that seemed unlikely to him, he had no idea if it was true. Unfortunately, prior to the invention of photography, what one person beheld could be conveyed to another only through word or art. Even today it is difficult to do an eclipse justice, as no photograph captures the corona exactly as the human eye sees it. Yet as spectacular as the corona was, Baily found another sight even more remarkable: three large red “protuberances” surrounding the disk of the Moon. Although he felt certain that they were associated with the corona, whether a part of the Sun or Moon he could not say.
The interplay of expectation and surprise in what Baily saw, like what Galileo experienced before him, is one of the greatest delights in any scientific investigation.cc Because of Baily’s meticulous observations, astronomers from all over Europe and the New World were eager to see if they, too, could discover something new about the Sun and Moon and these strange phenomena. To do so, according to Baily, was no longer possible by a single observer. Rather, the job of accurately recording all that there was to be seen during an eclipse required a team, each with his own independent piece of equipment dedicated to a particular phenomenon. Most importantly, if the Sun was to be understood, these teams of careful observers would need to travel the world to wherever new eclipses occurred.
Expeditions from England, France, and the United States would travel to every continent by commercial steamships, government gunboats, newly constructed continent-spanning railways, and even hot-air balloons. The astronomers who led them would climb high in the mountains of Peru in 1858, conduct observations in the Indian Himalayas in 1868, make beachheads on remote islands of the South Pacific in 1883, and travel across the sands of Algiers in 1900. Virtually every total solar eclipse that touched on solid land would be the subject of scientific expeditions for the next ninety years.
One British solar eclipse expedition in 1860 would mark the beginning of astronomy as most astronomers practice it today. Warren De la Rue was a pioneer in applying the newly invented technology of photography to astronomy, and he was determined to prove that the camera could capture the phenomena of totality just as well as the human eye. Through photographs, the mysterious features could finally be available for everyone to study and measure at leisure without depending on the artistic (or literary) abilities of the observer. Perhaps at last their origin would be discovered: Were the corona and red “flames” features of the Sun, or of the Moon?
De la Rue’s expedition was a major undertaking. His primary equipment was a special solar telescope with a custom-built cast-iron mount and forty-eight glass plates that he and his assistants carefully cleaned and packaged in London before departure. At their destination in Spain, the entire apparatus would be housed in a specially designed observatory that would double as a darkroom for developing plates. In the event the photographs were a failure (for no one had any measure for how bright the corona and prominences were, and therefore for how long to expose the plates), the expedition also carried a three-inch telescope to use for drawings. To this equipment were added boxes of developing chemicals, distilled water, engineers’ and carpenters’ tools, lanterns, oil, stove, kettle, and provisions in case the local countryside should be deficient in food (it was not). The entire expedition equipment list could be broken down into thirty boxes weighing a total of 4,133 pounds, transported by the British Admiralty ship HMS Himalaya from Plymouth, England, to Bilbao on the coast of Spain, and then by train to the interior town of Rivabello. It was a long way from Galileo and Baily and their simple pens and paintbrushes.
Fortunately, De la Rue’s photographs during totality were a complete success. From plates taken at the start and end of totality, it was obvious that the Moon moved across the corona and prominences. The conclusion was clear: the red “flames” and corona belonged to the Sun, and they must dwarf the Earth in size.
FIGURE 4.1. The first photograph of the totally eclipsed Sun and its bright prominences, captured by Warren De la Rue in 1860. (Image scan from the UCLA Library Collection, courtesy Royal Astronomical Society)
As much as they were a success for solar astronomy, De la Rue’s photographs were also a success for the impartial, mechanical eye of the camera over the artistic skill and transitory experience of the astronomer. The Australian astronomer H. C. Russell wrote about this change with some trepidation: “In many cases the observer must stand aside while the sensitive photographic plate takes his place and works with the power of which he is not capable. I feel sure that in a very few years the observer will be displaced altogether.” But other intellectuals were sure that even with new technology there were natural limits to what we could learn about these worlds beyond our atmosphere. In 1835, the prominent French philosopher Auguste Comte wrote in his Course de la Philosophie Positive (Positive Philosophy): “We can imagine the possibility of determining the shapes of stars, their distances, their sizes, and their movements; whereas there is no means by which we will ever be able to examine their chemical composition, [or] their mineralogical structure.”
This attitude seemed eminently reasonable given the astronomical distances between us and the stars, the planets, the Sun, and even our closest neighbor, the Moon. Without ever being able to travel to the heavens, the best we could ever hope to have is their light, and once you had seen (or later photographed) all that there was to be seen, what more could possibly be known?
Two hundred years earlier, Newton had discovered that hidden within sunlight were all the colors of the rainbow. All that it took to unlock them was passing the light through a simple glass prism. In 1800, William Herschel found that if you place a thermometer just beyond the red end of the rainbow, there is an unseen “color” there that contains a tremendous amount of heat: we now call it the infrared. A year later the ultraviolet was discovered beyond the blue. Over the next two decades, tiny gaps were discovered all across the solar spectrum where no color fell. Because the spectrum was best viewed when light passed through a narrow straight slit, these dark gaps were called “lines.” In 1859, just twenty-four years after Comte made his grand pronouncement, the chemists Gustav Kirchhoff and Robert Bunsen discovered that these lines were the fingerprints of the natural elements. Determine what fingerprint goes with what element, and suddenly anyone can sample the composition of the stars, no matter how far away.
We live in a world of seemingly endless variety. Yet everything we see is made of molecules that are a combination of only about one hundred different types of atoms. Even simpler, each of those atoms is nothing more than a combination of just three components: protons, neutrons, and electrons. Every atom consists of a nucleus composed of one or more positively charged protons (with some number of neutrally charged neutrons), circled by one or more negatively charged electrons. One proton circled by one electron is all that you need to make hydrogen, the lightest element there is. Six protons, fused together with six neutrons and encircled by six electrons, form carbon, the primary component of our bodies. Eight protons, eight neutrons, and eight electrons produce the most important constituent of the air we breathe: oxygen.
We picture electrons orbiting the nucleus as if they were tiny planets orbiting a sun. But unlike planets, electrons can only occupy specific orbits carrying specific amounts of energy. Any change from one orbit to another therefore requires a similarly specific change in energy. When an electron goes from a higher energy to a lower one, the excess energy is given off as light. The wavelength, or color, of light is simply a matter of its energy. Since each element has a unique set of energy levels for its electrons, each element emits or absorbs a unique spectrum of colors—its own elemental fingerprint.
Astronomers Pierre Jules Janssen and Norman Lockyerdd independently designed instruments to study these spectral lines from the Sun during eclipses. Of particular interest were the nature and composition of the mysterious red prominences. They found that the light of the prominences, rather than being a rainbow of light like the photosphere, was instead composed of just four distinct lines: two bright red and blue lines and two weaker yellow and green. Three of those lines—red, green, and blue—had previously been discovered in the spectrum of the simplest element of all: hydrogen. August Comte had been proved wrong. Without leaving our planet, Lockyer and Janssen discovered the composition of a world out in space. Rather than some celestial ether (the dream of the ancient Aristotelians), it was nothing more than the simplest of all elements found right here on Earth. Solar prominences, it was discovered, are just great geysers of hydrogen gas erupting off the surface of the Sun.
As for the other spectral line, when Lockyer found no element or conditions under which hydrogen emitted the remaining bright yellow line in the solar prominences, he proposed a new element named after the Sun god Helios: helium. That was in 1871. It would take another twenty-four years before this new element was discovered on Earth.
Helium, composed of two protons, two neutrons, and two electrons, is the second most abundant element in the Sun (right after hydrogen). Like hydrogen, Lockyer and other astronomers found it in the spectra of stars and gaseous clouds throughout space. The fact that the gases in our laboratory emit precisely the same spectral lines seen in the most distant galaxies—whose light has been traveling toward us since soon after the universe formed—means that the laws of physics are the same throughout space and time. As it is on Earth, so it is in the heavens.
That we see the presence of these common elements throughout space is an important clue to the life cycles of stars—and the origin of just about everything. To understand why, we must step back and first wonder why the Sun, like the stars at night, continues to shine. Is it possible that the Sun shines because it is on fire? If so, the light we see is due to the breakdown of molecular bonds. Chemists of the nineteenth century knew well what kind of energy molecular bonds released when they broke; given the rate at which the Sun shone, they found that if this were true, the Sun would run out of fuel in no more than a few thousand years. Such a short lifespan for the Sun was not a problem for a biblical origin of the Earth only 6,000 years ago. But the nineteenth century also saw expeditions other than those for eclipses. Charles Darwin’s expeditions on the HMS Beagle in the 1830s produced his work proposing the slow evolution of species over millions of years. This theory agreed well with his calculation, presented in the Origin of Species, that erosion would need 300 million years to create the geologic landscape he saw back home in England. It made sense that the Earth should be older than the life that inhabited it, but it would be impossible for the Earth to be older than the Sun that sustained it. The Sun couldn’t be on fire.
Did the Sun shine, instead, by the energy it released from its formation? Drop a rock from a high building, and there was no doubt that its impact released energy. An entire Sun’s worth of mass falling together from a distance spanning the solar system would release enough energy to light the Sun for nearly 20 million years. Yet even that was too short compared to Darwin’s geologic history. No adequate answer for why the Sun could shine for so long was known until the dawn of the twentieth century. Only then did the discovery of radioactivity and the components of the atom finally reveal a previously unknown energy source: fusion. Fuse small atomic nuclei together to form larger ones, and the energy released per mass is more than almost any other reaction.
Positively charged protons reside in the nucleus of the atom. To force them together, you need to overcome the tendency of like-charges to repel. Only incredibly high pressures and temperatures can fuse even the smallest atomic nuclei together. In 1920, the British astronomer Arthur Eddington (famous for an eclipse expedition of his own the previous year) accurately proposed that the only place these conditions were found naturally was in the hearts of the stars. Fusion was what fueled the Sun.
Our Sun is a mass of hydrogen gas a million times greater than the Earth. Gravity, the force that draws all things together, causes the Sun to collapse. But as it does, the pressure at its center grows until the hydrogen fuses to form helium, along with a tremendous amount of nuclear energy. The superheated gas swells like a hot-air balloon until it counters the gravitational collapse. The Sun, like every other star in the sky, is in a delicate balance between gravity pushing in and nuclear-driven heat pushing out. Eventually, the heat from the core, radiating out through the Sun, bubbles to the surface in enormous convection cells, like a rolling boil of water heated from beneath on a kitchen stove. The tops of these cells radiate their energy away into space as light. This is the photosphere that we see.
On Earth we are familiar with everyday things like oven coils and charcoal fires that give off light because they are hot. We call this thermal radiation. You and I are warm enough to give off infrared light, but not so warm that we glow at night with the lights off. The Sun, the stars, and the filaments inside incandescent lightbulbs are warm enough—that is why they light our world. The Sun’s photosphere is at a temperature of nearly 10,000oF (5,500oC) and thus radiates light in the visible part of the spectrum.ee The dark sunspots Galileo first saw are slightly cooler places within the photosphere. They form as different parts of the Sun rotate at different speeds (gas at the poles takes thirty days to make one trip around the Sun, while gas at the equator takes twenty-four). The Sun’s magnetic field twists and knots during this differential rotation until kinks pop out of the surface like a rubber-band twisted too much. Where this happens, the magnetic fields push the flowing hot gas aside and we see down into comparatively cooler, darker gas beneath.
Hydrogen atoms stream along the magnetic field lines that loop out of these spots, emitting the bright red line of hydrogen gas that first revealed their composition during eclipses. These are the prominences that together with sunspots increase in number as the kinks in the Sun’s magnetic activity ebb and flow over an eleven-year cycle. See an eclipse at the peak of the Sun’s activity, when solar magnetic fields are fully knotted and the surface is covered in spots, and you have the chance to see lots of bright red prominences. Eclipses halfway between those years tend to have fewer.ff
The source of the hydrogen we see in the prominences is a thin atmosphere of excited gas just above the photosphere. The red light of excited hydrogen gives this layer its color, which is also sometimes visible during solar eclipses, and is why we call it the chromosphere: chromo is Greek for “color.” Strangely, the chromosphere grows hotter the farther it extends from the Sun. Why it does so is still a subject of research. The leading hypothesis says that energy flows upward along the magnetic fields and is funneled into the upper atmosphere, particularly the corona above it, which can reach temperatures of millions of degrees.
Spectral lines given off by iron atoms that have had thirteen of their electrons ripped from around them are evidence of the extreme temperatures found in the corona. Until relatively recently, no lab on Earth could produce the conditions necessary for these lines. Astronomers at the turn of the last century thought they had discovered yet another new element in the Sun, which they called “coronium.” Only with the new understanding of atomic physics that developed during the early 1900s was the true origin of these lines, and thus the enormous temperatures of the corona, made clear.
Think about what these temperatures mean. Every star you see in the sky is glowing because it is a few thousand degrees hot. The very hottest stars are a few tens of thousands of degrees. But when you see a total solar eclipse, that corona you witness is millions of degrees hot; it is the hottest thing the human eye will ever see in nature. Yet it comes from a place so diffuse that the light it gives off is too faint to be seen unless the rest of the Sun’s light is extinguished. This is what our Sun is: a nuclear fusion reactor that has been producing helium and energy (and thus giving us life) for almost 5 billion years. It will continue to do so for another 5 billion more. But what happens then?
The British astronomer Fred Hoyle (who earlier hypothesized the eclipse-predicting potential of Stonehenge’s Aubrey holes) was the first to propose that once a star has run through its hydrogen fuel, the inward force of gravity eventually forces the fusion of helium into carbon, oxygen, and other elements in the periodic table. Since each new element requires even greater gravitational pressures to force them to fuse, the initial mass of each star determines the end product after which no new fusion is possible. For our Sun, the last element formed is carbon, after which its core collapses into a white dwarf star, a tiny ball of carbon atoms no larger than the Earth; the rest of its gases are blown out into space. For the most massive stars, where elements as complex as iron are made, the end of their nuclear production occurs in an explosion as bright as a billion stars shining all at once. During this supernova explosion, the atoms in the star collapse and then rebound, ripping the star apart from the inside out. For a fraction of a second, it becomes the universe’s largest particle collider, producing the other naturally occurring elements in our periodic tables. The star’s explosion scatters all of these atoms into space, and eventually they become incorporated into new stars (and the planets that form around them). The spectral lines of carbon, oxygen, and iron that we see in the Sun are only there because other stars lived and died long before ours ever formed. They are the source of the lead in our batteries, the silver in our banks, and the uranium in our warheads. The iron in our blood was formed in the ancient hearts of stars, and with every breath we take we breathe in the oxygen those stars left for us. They are a part of us: every atom in your body, other than hydrogen, was once an atom in the heart of a star. As the astronomer Carl Sagan said, “We are star stuff.”
This is a revelation both uplifting and humbling. It is the dream of the astrologers that we are intimately tied to the stars at an atomic level. At the same time it is a disquieting thought that the physicists who discovered this cosmic connection are many of them the same ones who found another, less uplifting use for nuclear processes. The physicist Hans Bethe, who discovered how helium is fused, went on to become the head of the theoretical branch of the Manhattan Project, which helped to develop the first nuclear bomb in World War II. Edward Teller, who discovered the energies produced in the nuclear fusion at work in stars, went on to do the same for the even more powerful hydrogen bombs. The fathers of stellar fusion are the fathers of the atomic and hydrogen bombs—bombs that for a brief moment unleash the conditions at the core of our Sun on the surface of our tiny planet. How appropriate then that Zeus, in his anger at Prometheus for stealing the celestial fire, sent evil into the world locked in a box. Like Pandora, in our curiosity we opened it.
But there is another use for nuclear fusion on Earth. Should we ever find a way to safely reproduce the nuclear fusion in the Sun, using the hydrogen in simple seawater, we will unleash the power of the stars using a process that leaves behind no radiation or greenhouse gases. We would be using a fuel that is found everywhere, virtually free, and practically limitless.
Eddington spoke presciently when he said, in 1920: “If, indeed, the sub-atomic energy in the stars is being freely used to maintain their great furnaces, it seems to bring a little nearer to fulfillment our dream of controlling this latent power for the well-being of the human race—or its suicide.” It is important to remember, then, that although evil may have escaped from Pandora’s Box, the one thing that didn’t was Hope. After 5 billion years, we are the universe on Earth: the stars made sentient.
a The British mathematician Thomas Harriot actually pointed a telescope at the Moon four months before Galileo. But he made no more than a rough sketch of what he saw, noting the date and time and nothing more. What he thought about the light and dark regions that he saw he wrote in no journal; nor did he share it with any colleague. As a result, his name remains little more than a footnote in the history of astronomy.
b In 2003, a dozen major forest fires raged around Southern California. I was living under one of the smoke plumes and still remember looking up through the ash-darkened sky to see a blood red Sun with two black sunspots for eyes looking back down at me. It was the eeriest thing I’ve ever seen.
c The most exciting statement a scientist can utter is, “Huh, that’s odd.”
d Lockyer was also the first person to study ancient temples and monuments, including Stonehenge, for astronomical alignments.
e Cooler gases just above these convection cells absorb their characteristic fingerprints of color from the light streaming by and thus are the source of the “gaps” seen in the light emitted by the Sun.
f The 2017 solar eclipse will be at minimum solar activity. The 2024 solar eclipse that crosses the eastern United States will be near solar maximum.