Accessory to War

by Neil DeGrasse Tyson

  What does it take to build an empire? What resources must be consumed to sustain one? Why do some people hunger for power while others shun it? What nations, if any, must be inculcated or invaded by other nations to achieve security—real or imagined? Which people, if any, must be placated or silenced to prevent uprisings? What must get broken and who must get killed to achieve these ends?

  Centuries ago, Christiaan Huygens contended that war and commerce had “forc’d out . . . most of those Discoveries of which we are Masters; and almost all the secrets in experimental Knowledge.” With only rare exceptions, history shows that while strategy and bravery can win a battle, the frontiers of science and technology must be exploited to win a war. Though the night sky itself is the quintessential frontier, the astrophysicist neither declares war nor makes international enemies. Countries manage that with no help from scientists. Yet for every empire the world has known, skywatchers have been in attendance, offering arcane cosmic knowledge that has been enabled by, and has also reinforced, the power wielded by leaders—leaders who sought the highest ground and judged, once again, that it was time to kill.

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  STAR POWER

  Throughout much of history, knowledge of the heavens informed the rhythms of life and the mastery of territory. Astronomy moved arm in arm with agriculture, trade, migration, empire, and war. It created and marked time; it registered place on Earth. It was both a sacred mystery and a blue-chip stock. Astronomers wielded power and served the powerful.

  Millennia before anybody had drawn usable maps of the continents, people memorized imagined maps of the sky. Long before there were astrolabes or sextants or precision portable clocks to establish distance, latitude, and longitude, people gauged their position with no tools but their eyes and the sky. To go where no one had gone before, to know how long it took to get there, and to return there if you liked what you found, you needed guides. The sky was a good one, especially if your path lay across uncharted ocean, unstable dunes, sweeping grasslands, or barren tundra. Heaven itself was both compass and clock, direction-finder and time-keeper. For many, it was also ultimate cause, crystal ball, and the home of deities—astronomy, astrology, history, folklore, religion, psychology, and poetry rolled into one. Knowing the rhythms of the sky was a means to knowing the character and fate of all things.

  It’s anybody’s guess when and where a community chronicler, or maybe an insomniac, first decided to track the cycles of change in the Moon’s illuminated disk, or the alternate lengthening and shortening of the Sun’s arc across the sky, or the periodic comings and goings of Venus. Such tracking would have predated the first stone tools. Maybe an antecedent of Homo sapiens was the first to do it. Whoever it was and whenever it happened, that signaled the birth of astronomy, a source of both wonder and power for our nascent species.

  Consider units of time. If the Sun never set and the Moon never waned, our measures of time might be grounded solely in biology—the beating heart, circadian rhythms, menstruation—because “periodicity is part of who we are.”1 But the Sun does set, and the Moon predictably waxes and wanes. Transitions recur endlessly in the skies above. Celestial cycles offer themselves as a natural measure of time in units we care about.

  Earth’s early cultures, population centers, and central governments required official methods of organizing time, especially when they needed to plan ahead. Sacrifices, festivals, planting, harvesting, tax collection, daily work shifts, and daily prayers took place at predictable intervals. In Upper Egypt, farmers needed to know when the dazzling Dog Star, Sirius—the brightest star in the night sky—would appear in the dawn sky just before the rising Sun, because that was when the Nile, too, would be rising. Hunters, gatherers, herders, and nomads also required advance planning: their lives depended on knowing when the regional waterholes would dry up, when the cattle or gazelles or bison would give birth and the eggs of the mallee hen could be stolen, when to visit the wild strawberry patches and when to dig up the yams. It was useful to know how many days’ travel were needed to reach the nearest oasis. It was useful to monitor fertility. Everybody needed ways to track the passing days.

  More than twenty thousand years ago, people made notches in animal bones and painted rows of dots on the walls of caves to mark the days of a lunar cycle.2 But no round number of lunar cycles matches the duration of the solar year, a discrepancy that gave rise to continual fussing with calendars. Several early cultures followed a twelve-month year; some added the occasional thirteenth month or five-day bloc to keep things on track. Discrepancies notwithstanding, sometime around the middle of the fifth millennium BC the Egyptians counted the correct round number of whole days in a year. They also devised a 365-day solar calendar that began with the rising of Sirius on July 19, 4236 BC—possibly the earliest secure date in history.3

  Unlike the solar day, the lunar month, the Earth year, or the other celestial cycles that our ancestors could observe, subunits of time such as the hour, the minute, and the second are a matter of cultural and mathematical taste. Sociologically, they suggest the emergence of oversight, labor, standardization, and penalty: slaves and prisoners on construction gangs, priests reciting prayers at fixed intervals, sentries posted for a fixed watch—and, more recently, trains running on time, workers punching in, and spacecraft systems synchronized for launch. On a more personal level, they suggest practicalities and annoyances such as waiting for the bread to finish baking or your mate to return home. Enter the clock, whether based on a moving shadow (the obelisk or sundial), flowing water (the clepsydra), an advancing gear, a swinging pendulum, or a transitioning electron in an atom of cesium.

  The Sumerians divided the day into twelfths, and each twelfth into thirtieths. The Egyptians divided both day and night into twelfths: voilà, the twenty-four-hour day. The Babylonians came up with the fraction-friendly sixty-minute hour and sixty-second minute. But not all units of time are as practical as the minute or the month. Plato, for instance, wrote of the “perfect year,” the period necessary for all the planets to return to their initial configuration. A scheme devised by the ancient Hindus employs even vaster units, such as the kalpa, the length of a single day or single night in the lifetime of Brahma, who dreams the universe into existence each time he sleeps. When he awakes, the universe begins anew; 4.32 billion years later, when he next falls asleep, it vanishes. The Maya, too, formulated an overview of time based on attenuated cycles of creation; the most recent cycle expressed through their complicated “long count” began on August 12, 3114 BC.4 Nor did such imaginative conceptions cease in the modern world. A mystical quasi-mentor of Adolf Hitler’s, for instance, foretold that the 730-year “cosmic week” beginning in 1920 would, because of Jupiter’s entrance into Pisces, bring about the millennarian triumph of blond Christians under the wise and genial rule of aristocrats, priests, and führers.5

  Besides marking time, there was the challenge of mapping the sky. If Heaven was the fount of fortune and disaster, prudence demanded that the stars and the constellations they trace be demarcated and monitored. Some early Chinese astronomers divided the sky into the Five Palaces; others divided it into the Nine Fields or the twelve Earthly Branches or the twenty-eight Lunar Mansions. Early Mesopotamian astronomers divided the eastern horizon into the paths of three gods, with sixty fixed stars and constellations rising within the paths; later Mesopotamian (Babylonian) astronomers divided the sky into twelve segments, each associated with a constellation and each enclosing thirty degrees of the Sun’s yearlong path across the sky—forming the now-classic twelve constellations of the Western zodiac.

  Inevitably, references to the cosmos show up in the art and architecture of antiquity. Cuneiform tablets inscribed five thousand years ago in Mesopotamia mention the Bull (Taurus), the Lion (Leo), and the Scorpion (Scorpio). A tablet inscribed almost four thousand years ago in the Mesopotamian city of Nineveh lists the apparitions of Venus during the reign of King Ammisaduqa. The arched ceiling of a first-century BC Han dynasty tom
b unearthed on the campus of Jiaotong University in Xi’an, China, presents a painted diagram of the heavens showing the Sun and the Moon surrounded by a circular band filled with symbolic figures representing the twenty-eight “lunar lodges” that mark the path of the Moon.6

  Scattered across our planet are enormous stone temple ruins and looming stone monuments whose structure reveals well-established knowledge of sky patterns. In the ancient world, architecture, owing in part to the expense, labor, and time necessary for its construction, was the very embodiment of state and religious power. Among the oldest undisputed monuments with a celestial tinge are the fourth millennium BC stone “passage tombs” of County Meath, Ireland: low burial mounds where, at the winter solstice, sunlight streams through an opening above the entrance and illuminates a long passageway leading to a large chamber.7

  Doorways and sight lines of massive stoneworks—whose many-ton components were, in some cases, quarried, transported, shaped, and positioned without the aid of metal tools—align, perhaps not precisely but still convincingly, with the rising or setting Sun at the spring equinox or winter solstice, the setting full Moon at the summer solstice, the cardinal directions, or the apparitions of a planet or the never-setting Pole Star. The slew of far-flung examples include the pyramids at Giza, stone circles throughout the British Isles, roofed temple complexes in Malta, octagons in the Basque region, the Caracol at Chichén Itzá, the Templo Mayor in Mexico City, and the Thirteen Towers at Chankillo, Peru, which consists of a row of towers strung across a ridge plus two observation structures, one to the west and one to the east. Other, more modest constructions embody the same principles: at Nabta Playa in southern Egypt, two upright stone “gates” in a small circle of sandstone slabs, akin to a small Stonehenge, align with what would have been the position of the rising Sun at summer solstice.8

  In fits and starts, astronomy became a science. During the first millennium BC, the astronomers of Mesopotamia and China—in the service of hereditary rulers, warrior-kings, and eminent priests—compiled systematic records of what happened before their eyes and developed systems and even instruments for predicting what would happen in the future. About fifteen hundred Late Babylonian clay tablets, in the form of diaries chronicling routine observations, have been found to date. Spanning eight centuries, the tablets list such things as lunar eclipses, weather conditions, intervals between moonrise and sunrise and between sunset and moonset at different times of each month, and the changing positions of the planets in relation to thirty-one reference stars. By about 500 BC, Babylonian astronomers had devised mathematical ways of predicting the dates of new and full Moons. The world’s earliest known record of a series of solar eclipses, between about 720 and 480 BC, comes from China. By 200 BC, Chinese court astronomers had begun to chronicle most celestial phenomena visible to the unaided eye, both cyclic and episodic, whether or not they understood what they saw: auroras, comets, meteors, sunspots, novas, and supernovas, as well as the paths of planets month by month. The presumed relationship between the unfolding universe above and the affairs of state below rendered this record-keeping a guarded activity. In today’s parlance, it was classified research.9

  When I was a postdoc at Princeton University in the early 1990s, a graduate student specializing in ancient Chinese culture stopped by my office with a query about a certain historical date. Sometime around 1950 BC—he couldn’t pinpoint the year—major events had taken place in China, and he suspected that some kind of sky event had preceded them. He was right.

  Whipping out my planetarium sky-search software, I discovered that February 26, 1953 BC, corresponded with the tightest conjunction of planets ever witnessed by civilization: Mercury, Venus, Mars, and Saturn gathered on the sky within half the area of your pinky fingernail held at arm’s length (half a degree), with Jupiter two finger-widths away (four and a half degrees), creating a conjunction of all five known planets. Four days later, the very thin, waning crescent Moon would join the jamboree. All six objects were now nicely contained within the top-to-bottom area of your fist at arm’s length (ten degrees). Other spaceniks with equal access to computational tools would independently discover this alignment.

  Although uncertainties abound when you’re trying to date events from early history, it turns out that 1953 BC just may coincide with the founding of the Xia Dynasty by its first ruler, Yu, of whom it was recorded in the Xiaojing Gouming Jue: “At the time of Yu the planets were stacked like strung pearls.” More important, the first-century BC Hong Fan Zhuan (“Account of the Great Plan”), now lost, declared that a new calendar began on a spring morning in about 2000 BC during a five-planet conjunction with the new Moon. All of which makes the February 1953 BC conjunction a convincing candidate for the start date of what became the modern Chinese calendar.10

  While the Chinese were occupied in observing and recording the behavior of objects, the Greeks were expanding astronomy’s reach, making it both more conceptual, more practical, and more accessible. Empowered by geometry, they began to measure and map the universe as no civilization had done before. Triangulation, an idea set down in Euclid’s Elements (ca. 300 BC) as a pure mathematical statement, proved useful for estimating the distance between Earth and the Sun. Several centuries after Elements hit the market, an expert toolmaker—perhaps on the island of Rhodes, likely in collaboration with an astronomer—built a sophisticated calendar/astronomical computer/almanac/planetarium known today as the Antikythera Mechanism, perhaps the most-debated scientific object from the ancient world.

  Alexander Jones, a classicist and historian of the mathematical sciences, proposes that the Antikythera Mechanism be called a cosmochronicon. Found along with other high-end cargo in a large Mediterranean shipwreck at a depth of 180 feet, and fitted with dozens of bronze gear-wheels, a hand crank, multiple dials, and multiple inscriptions, it was a shoebox-sized creation that could calculate the phases of the Moon, the changing longitudes of the Sun, Moon, and planets, the timing of eclipses, solstices, and equinoxes, and several long-term time cycles. Investigators derive its date—most likely first century BC and certainly no later than first century AD—from such factors as the Hellenistic-era vocabulary and lettering in the inscriptions, the state of astronomical knowledge incorporated in the object, and the scores of coins found nearby in the wreck. Though almost shocking in its sophistication, the Mechanism does have several known antecedents. It also has a cultural context: astronomy was treated as a topic suitable for popularization (think Cosmos and Star Talk rather than the guarded cosmic secrets of ancient imperial China), and both public and private spaces in the Mediterranean world were liberally sprinkled with astronomy-related objects, such as sundials large and small, armillary spheres, star globes, and stone tablets called parapegma, which had movable pegs that fit into holes beside each numbered day and served as public almanacs. The Antikythera Mechanism, whose complex inner workings have recently been revealed through X-ray computer tomography (CT) and whose surface details have become more legible through reflectance imaging, strikingly exemplifies the Greek concept of “uniformly flowing time that could be measured on instruments.”11

  Physics, too, now came to the fore. Ever since the second century BC, writers have been recounting the story of the Greek mathematician and military inventor Archimedes, who, they say, devised a “burning mirror” in about the year 213 to redirect and focus the Sun’s rays onto a fleet of Roman ships anchored in the harbor of Syracuse, thereby, in the words of Lucian, “set[ting] ablaze the triremes of the enemy through art.” But even before Archimedes did (or didn’t do) it, mathematicians and engineers had begun to consider what a workable burning mirror would look like. The earliest detailed analyses concluded it would have to be concave, perhaps parabolic, and made up of an array of at least two dozen hinged, movable mirrors rather than just one. Presumably the mirrors would be large and cast of polished bronze. To this day, mechanical engineers, teenage science-fair types, and TV crews stage the occasional simulation of Archime
des’s endeavor, some resulting in out-and-out failure, some in qualified success.12

  Despite astronomy’s growing practicality, celestial events could still provide a potent magical kick. Sometimes they even swayed the course of history. Rulers could be dethroned because of a comet or a supernova. Battles were launched, won, lost, or abandoned because of an eclipse. The day Odysseus rejoined his waiting and presumably widowed wife and slaughtered the hordes of suitors who had been hanging out at his house may well have coincided with a noontime eclipse in 1178 BC.13 And Herodotus—the fifth-century BC war historian, travel writer, and investigative reporter—recounts the effect of an eclipse during the sixth year of battle between the Lydians and the Medes. The participants, he writes, were so shocked to see “day on a sudden changed into night” that both sides stopped fighting and started negotiating.14 Modern eclipse calculations, based on celestial mechanics, yield a precise date for that armistice: May 28, 585 BC, at about 7:30 PM. While the time of an ancient event is often uncertain, its location is typically well-documented. For this reason, total solar eclipses have served as a type of laboratory, permitting a comparison between where you would have expected to see a given eclipse, based on the assumption that Earth’s rotation rate has been constant over the millennia, and where the eclipse was actually observed on Earth. That these turn out to be two different locations on our planet’s surface offers incontrovertible evidence that Earth’s rotation rate has been slowing down, primarily due to friction from oceanic tides sloshing on our continental shelves. In modern times, this phenomenon is well-known and well-measured, which has led to the occasional addition of a “leap second” to the calendar.