The Antikythera Mechanism: the First Horoscope Computer

The Antikythera Mechanism is the most sophisticated ancient tool ever discovered. Indiana Jones and the Dial of Destiny uses the mechanism for time travel. The real story is more intriguing. The First Horoscope Computer I n 1900, Greek sponge divers working off the island of Antikythera found the remains of a large ancient cargo vessel. The latest coins found in the wreck tell us it must have gone down around 67 BCE, when the Roman Republic under Pompey the Great was sweeping the eastern Mediterranean clean of pirates. Spilled out on the sloping seabed were bronze and marble statues, presumably destined to ornament Roman temples and gardens as plunder from a successful military campaign. BY BRADY KIESLING Antikythera Mechanism Fragment A, the largest surviving remnant (National Archaeological Museum, Athens, Kostas Xenikakis, photographer) 28 spiritualityhealth.com march / april 2024 National Archaeological Museum, Athens, Kostas Xenikakis, photographer © HELLENIC MINISTRY OF CULTURE / HELLENIC ORGANIZATION OF CULTURAL RESOURCES DEVELOPMENT (H.O.C.RE.D.). (2) march / april 2024 spiritualityhealth.com 29 Fragment A with X-ray image: drive wheels and solar-lunar gearing (National Archaeological Museum, Athens, Kostas Xenikakis, photographer) 30 spiritualityhealth.com every buried surface, count every gear tooth, and ultimately reconstruct a virtual working model of the Mechanism that, in its general outlines at least, must be correct. The Antikythera Mechanism, with its bronze plates and gears anchored in a wooden frame, was a working model of the zodiac and its denizens. Turn the crank and the main pointer on the front dial shows the position of the sun running its course on the zodiac, one revolution every 365.25 days. Smaller concentric rings show the positions against the zodiac constellations of the five visible planets, plus the moon with its phases and nodes. One ring could be removed, adjusted by a day, and replaced, allowing this star alignment to be matched to a specific month and day of the sacred 365-day Egyptian calendar. On the back plate were two spiral dials, one generating a highly accurate lunisolar calendar using the 19-year Metonic cycle (used by the Hebrew calendar as well), the other a monthly map of the Babylonian Saros cycle to predict eclipses of sun and moon. Lists of important astronomical events with their dates were engraved on one plate, cycles of planetary movement on a second, and user instructions on the back cover. In effect, an ancient craftsman crammed a thousand years of Babylonian and Egyptian astronomical wisdom, whole libraries of clay tablets and papyrus scrolls, into a bronze device a little more than a foot high and seven inches wide, linking these observations to a quasi-universal calendar. With patience and care, you could recreate the configuration of the major features of the night sky for any given date within a century or so. THE RANGE OF ANCIENT TIMES We should remember that the ancient world had no Naval Observatory to tell us what day it was, nor what year. Each city labeled its years unintelligibly to outsiders, with the name of a local priest or magistrate or king. The civic year began, usually, with the first new moon after a solstice or equinox. Each month was linked to a god, each god to a sacred day and festival, and each festival to some feature of the agricultural year, so lunar months and solar years had to stay synchronized. To achieve that, some months had 30 days and others 29 to match the moon’s 29.5-day period. Every two or three years, a city would insert a thirteenth month to keep its year in tune with the seasons. Different cities started their year at different points, omitted days at different points, and inserted their extra month at a different part of the calendar. Occasionally, politics required them to manipulate their calendar more brazenly, such as when the Roman emperor Nero showed up in Athens in the wrong month for the Mysteries—and it suddenly became the right month. To cope with such complexity, the back plate of the Mechanism had an idealized spiral of 235 whole lunar months fitted into 19 whole solar years, with an indication of when to delete days or insert months to keep the gods synchronized with their festivals. Next to it was a smaller four-year dial marked with the names of six major ancient athletic festivals conducted during a four-year cycle. It was by counting Olympiads from 776 BCE that Greeks aligned their year numbers from city to city. Another small dial refined and extended the 19-year Metonic cycle by indicating when one extra day should be omitted every 76 years. An enormous history of time from all over the known world was built into this device. © HELLENIC MINISTRY OF CULTURE / HELLENIC ORGANIZATION OF CULTURAL RESOURCES DEVELOPMENT (H.O.C.RE.D.). (2) These rare pieces of classical art attracted a huge salvage operation, one that continues to this day. At first the specialists had no time for a few clumps of corroded bronze the divers tossed in baskets and sent to the surface. But when the lead Greek archaeologist looked more closely, a nest of interlocking gears and a few decipherable words in ancient Greek signaled a thrilling discovery. This was a sophisticated astronomical device, one centuries older than any remotely similar surviving object. But even the most careful effort to clean and analyze the Mechanism broke it into smaller and smaller bits of dark green crud. Ancient literature provided tantalizing hints as to its purpose. The Roman politician-philosopher Cicero mentions a sphere showing planetary movements produced “just recently” (ca. 80 BCE) on the island of Rhodes by his Greek friend and teacher, the Stoic polymath Posidonius. Elsewhere, Cicero recounts that that the prize possession of Metellus, the conqueror of Syracuse in 212 BCE, had been a similar sphere created by the great physicist and engineer Archimedes, one that accurately traced the complex movements of sun and moon to demonstrate how eclipses worked. Cicero wrote, “I concluded that the famous Sicilian had been endowed with greater genius than one would imagine it possible for a human being to possess.” A century after the Mechanism’s discovery, the tools became available to confirm that such brilliance indeed existed in antiquity. In 2005, a portable X-ray scanner dissected the corroded lumps of bronze into micrometer slices, reintegrating as digital images each of the dozen or more layers of metal the larger fragments contained. Scientists could then read every preserved letter on march / april 2024 Fragment 19, Greek user manual from the Back Plate (National Archaeological Museum, Athens, Kostas Xenikakis, photographer) © HELLENIC MINISTRY OF CULTURE / HELLENIC ORGANIZATION OF CULTURAL RESOURCES DEVELOPMENT (H.O.C.RE.D.). WHAT THE DEVICE IS NOT The Antikythera Mechanism is not a navigational device—the coordinates you could extract from its pointers would put you somewhere in the eastern Mediterranean, whereas looking out a porthole could generally place an experienced Aegean sailor within a mile. The Mechanism is not a clock or a calendar— no Greek needed an analogue computer to keep track of what day it was, or of what major festival was due. A single sheet of papyrus could contain all the information required, perhaps with a little help from a sundial or a glance at the sky. The Mechanism was too small and fragile to serve as a public display of anything. If you turned the crank enough times, it would show you the planets suddenly and mysteriously changing direction at intervals—but only along a single track. A bronze celestial sphere—a much simpler invention—would be more useful if teaching students astronomy were the goal. MODERN SCIENCE AND ANCIENT WISDOM Astrology earned its reputation as the exact science of its era thanks to the centuries-spanning databases compiled by Mesopotamian and Egyptian priests. Their astral records correlated the sun, moon, and planets to actual earthly events: The river waters began to rise. You could buy this much barley for a shekel. “The 29th, the king died.” The 29th in this cuneiform tablet equates to June 10/11 of 323 BCE, and the king who died that day in Babylon was Alexander the Great. Undoubtedly, the heavens had been full of dire portents for this worldchanging event, just as they had accurately forecast with eclipses and rains of fire Alexander’s victory over Persian King Darius at Gaugamela nine years before. But it was cloudy in Babylon the week Alexander died. With the Antikythera Mechanism, if you turned the crank backwards enough times, you could determine the exact conjunction of heavenly signs that had signaled doom for Alexander, the signs the Babylonian priests had been unable to observe. If astrological prediction was to be rigorous in telling kings what days and people to avoid— in any weather—scientific tools like the Antikythera Mechanism would be of enormous help. march / april 2024 spiritualityhealth.com 31 Dodona ancient theater WHAT IT DID The Mechanism is designed to do one thing well: to generate for any given month and day in any Greek calendar (provided you knew the Olympiad or Egyptian year number) the position of the sun, moon, and planets against the zodiac. Modern astrologers have printed tables to look up such information when casting horoscopes. By the late first century CE, so did Greco-Roman astrologers. When the Mechanism was built, in the three decades on either side of 100 BCE, the fashion for astrological prediction was just reaching Rome, rather to the disgust of Cicero. The Roman consul Octavius had a reassuring horoscope tucked in his toga when he was murdered by political rivals in 87 BCE. Before the Mechanism existed, only a professional astronomer could cast an accurate horoscope. Using it, almost anyone could. Yes, it took a priest well-versed in Egyptian or Babylonian astrology to legitimately interpret what the horoscope foretold. But plausibility was attainable by lesser mortals, too. An astrological use for the Mechanism in no way discredits the huge advance in theoretical astronomy, nor the engineering that the device represents. The Babylonians were content to record every apparent squiggle of a planet’s orbit as an arithmetic series without explaining why. Greeks, enthralled with geometry, assumed the gods who set the planets in motion were enthralled as well. Using perfectly circular gears suitable for perfect gods, Greek engineers at first failed miserably to match the planetary motion to the Babylonian numbers. By displacing the main axle of each planet gear a little off-center, then adding a smaller gear called an epicycle on top and triggering it with a pin sliding in a slot, you could persuade a planetary disk to slow to a stop, reverse direction, then resume its course—just as actual planets do. The challenge of building a prototype of the Mechanism inspired Hipparchus and his fellow Greek astronomers to the theories of deferents and epicycles that, refined by the great astronomer (and astrologer) Ptolemy, would explain the heavens until the days of Kepler and Newton. MONKEY BUSINESS AT ZEUS’ ORACLE AT DODONA Dodona was second in prestige only to Apollo’s oracle at Delphi. Most of its clients were local people writing their questions on scraps of lead sheet: Do I marry X? Do I invest in shipping deal Y? And then lots were drawn under Zeus’s sacred oak tree for the answer. Dodona’s most notoriously accurate oracular prediction, preserved by Cicero in his dialogue On Divination, was given in 371 BCE, when the Spartans asked the oracle how best to defeat the Thebans. As the priestess prepared to draw the lots, a loose monkey scattered the sacred paraphernalia. To Cicero, as to the WHERE IT CAME FROM Modern scholars are probably correct in assuming the Mechanism was produced on the island of Rhodes. If such devices had been widely manufactured, Cicero would certainly have seen one with his own eyes before his death in 43 BCE. With its civic cult of the sun god Helios and close commercial connections to Alexandria, Asia Minor, and Rome, Rhodes attracted astronomically minded philosophers, such as Hipparchus and Posidonius. The Mechanism’s calendar dial includes the Heliaia Games, an important festival for Rhodes but nowhere else. The dated astronomical phenomena on the cover plate fit well with the latitude of Rhodes. The shapes of the etched letters are a reasonable match for those on Rhodian inscriptions from the period 150 to 50 BCE. uses Greek month names distinctive to Epirus, a remote region of northwest Greece. The Epirote cities were systematically devastated by Roman legions in 167 BCE, their citizens enslaved. At the time the Mechanism was built, no individual or city in Epirus was in a position to indulge in expensive, cuttingedge science. One Epirote institution, however, still commanded international respect: the ancient oracle of Zeus at Dodona. Note that the Mechanism’s calendar dials feature, in addition to the Olympic games and the Heliaia, the obscure Naia games held every two years in honor of Naian Zeus at Dodona. The Antikythera Mechanism would have seemed a miraculous updating of Dodona’s traditional expertise in prophecy. Very likely, the Mechanism was a gift, a sacred dedication to Zeus, perhaps from the city-state of Rhodes, or perhaps from some eastern monarch or a wealthy Roman student. WHO WAS IT FOR? We have a couple of hints for whom the Mechanism might have been customized. The calendar spiral 32 spiritualityhealth.com march / april 2024 Such attributes are meaningless to modern astronomers but track perfectly with ancient omen manuals where eclipses foreshadowed catastrophic events: plagues, earthquakes, the death of rulers. The direction of the wind, for example, allows you to determine toward what country the eclipse’s evil influence is directed. GETTYIMAGES.COM / LEAMUS dial are blank, but some have tiny letters specifying a solar or lunar eclipse, an approximate hour, and an index number. This index links the eclipse to one of six eclipse descriptions etched in the plate. Those descriptions include the size and color of the eclipse but also which way the winds are blowing at the beginning and end of the sun’s disappearance. GETTYIMAGES.COM / THEROFF97 THE SAROS CYCLE AND THE SCIENCE OF BELIEF The lower back spiral dial demonstrates that the builders of the Mechanism did not separate the science of astronomy from the conviction that motions of the sky correlated to events on earth. The Saros cycle is a numerical pattern of 223 lunar months first compiled by Babylonian astronomers to identify months in which an eclipse is possible. Most months of the priestess, the omen was clear: Forget victory, Sparta; it’s time to save your butts. Cicero was convinced the gods sent signs mortals could read. So was his friend Posidonius, inventor of a planetary sphere. So were all the scientific astronomers we know of from that period. Kings of Persia and Egypt subsidized philosophers and temples because the philosophers and priests WHY UNIQUE? Modern craftsmen replicating the Mechanism estimate that cutting and adjusting the dozens of gears, with 17 or 53 or 223 triangular teeth, using a metal file would take a specialized craftsman about a year under close supervision by an astronomer. This would have been an expensive tool for divination. And it was unlikely to stay usable for long. Modern machine-forged steel gears wear and slip; the Mechanism’s bronze gears had no such precise tolerances even before you ground them together a understood the world in accordance with theories of the cosmos that made their knowledge relevant to kings. Drawing lots under the oak tree began to feel rather primitive. The Antikythera Mechanism would seem an inspired upgrade to Dodona’s oracle, a decisive answer to monkeys and other charlatans competing for their business. few thousand times. The owners would want to think carefully, therefore, before turning the crank backwards three decades to cast a nativity for someone. Most likely these horoscope-generating powers were reserved for official delegations and the wealthiest of private supplicants. In any case, For more information, some inaccuracy was a given, particuread Alexander larly for the subtle motions of the key Jones’ A Portable astrological planet Mars. Cosmos: Revealing the Users evidently concluded within a Antikythera Mechanism, few years that astronomical charts on Scientific Wonder of papyrus scrolls were an adequate subthe Ancient World, stitute. To its inventors and sponsors, published by Oxford University Press in 2017. however, the Antikythera Mechanism will have seemed a truly transformative tool for mankind’s understanding of itself in the universe. These unknown scientists deserve to stand high in the ranks of human brilliance. Modern historians of science, therefore, should feel deeply unsettled. Had it not been for a nameless ship’s captain who failed to turn the crank and read the message of the heavens, modern scholars would be doomed forever to underestimate the passion and resourcefulness of their ancient Greek predecessors. Brady Kiesling is a former US diplomat and archaeologist who has written books on diplomacy and Greek terrorism and is the creator of the app ToposText, a free digital library of ancient texts mapped to the places and people they mention. topostext.org. march / april 2024 spiritualityhealth.com 33