摘录

Astronomy: Sky Watchers and More China Chinese astronomy resembles most other premodern sky technologies in that it was driven by divination. Yet Chinese astronomy differed from all others. It was run solely by a government bureaucracy and based on a worldview that said the ruler was "emperor under all heaven" - a divine appointment. Yet the connection between celestial events and human fate was perhaps even more profound. The link was not just between heavenly deities and the emperor; the earth, the emperor, and the entire cosmos were bound together in one gigantic entity, a superorganism in which the five elements, or "phases" - fire, air, wood, earth, and water - were in constant interaction as they sought their affinities with one another. Yet in China as elsewhere, portent astrology called for careful and regular observations of celestial events. The cosmic importance of every omen in the sky demanded that its results be noted down in detail. As a consequence, the Chinese possess the longest unbroken run of astronomical records in the world, observations of considerable importance to modern astronomers, whose research requires data about long-term celestial events. China developed astronomy very early in its history. Evidence goes back five thousand years. The ancients wrote stars-laden texts in many forms - on wine jugs, tortoise shells, and silk. The earliest records from archaeological sites in Qinghai Province consist of ceramic fragments on which are painted images of rayed sun disks and moon crescents. A piece of bone found to be thirty-five hundred years old contains writing showing that the Chinese already knew the length of the year to be 3651Ä4 days. There is evidence of star observation from before the twenty-first century B.C.186 The first recorded astronomical inscriptions date from the sixteenth to nineteenth centuries B.C. in the Shang kingdom of Henan Province. These artifacts are examples of an astronomical-divination system, technically called scapulimancy, a technique going back to Neolithic times. Selecting an ox or deer shoulder blade (scapula) or a tortoise shell, the diviners then dried, polished, and drilled the material with holes. They inserted a hot metal brand into one hole and examined the pattern of resulting cracks in the bone or shell. The diviner noted both the prognostication and later results on the cracked material. The oracle bones' existence was lost to the modern world until 1899, when a scholar from Peking became ill and sent his valet to a drugshop for medicines. One ingredient in the potion the pharmacist sent him was labeled "dragon's bones." The scholar realized it was bone chips with words inscribed on them in ancient Chinese - oracle bones. During the following decades the bones were traced to a field near An-yang, around three hundred miles southwest of Beijing. During the 1920s and '30s, some twenty-five thousand oracle bones were excavated there, from what may have been a palace archive. At least 135,000 more pieces have been excavated since, forming a treasury of information going back to Shang times. This vast library recorded on the bone texts has enabled modern historians of astronomy to backtrack regularly occurring celestial events with computers to match sky phenomena inscribed millennia ago. Recently, NASA astronomers used fourteenth-century B.C. oracle bones to help determine how much the earth's rotation is slowing down. Based on analysis of the tortoiseshell inscriptions, Kevin Pang and his colleagues at the Jet Propulsion Laboratory at Pasadena reported they had fixed the exact date and path of a solar eclipse seen in China in 1302 B.C. That, in turn, led them to calculate that the length of each day was 47Ä1,000 of a second shorter in 1302 B.C. than it is today. A cache of five thousand pieces of oracle bones excavated in An-yang in 1972 yielded a series of divinations of sky events. The Chinese astronomical historian Zhang Peiyu found that six dates recorded in the inscriptions matched perfectly with a series of solar eclipses visible from the Henan area in the twelfth century B.C., half a millennium earlier than records of such events obtained from Babylonia or Egypt. Other Shang bones yielded inscriptions of lunar eclipses. A reconstruction of another bone recording from around the same time revealed the observation of a supernova. The supernova inscription, perhaps the most ancient extant record of a nova sighting, says, in part, "On the seventh day of the month...a great new star appeared in company with Antares." The Chinese called these supernovas "guest stars." Thus the Chinese knew well what they were observing when, in June 1054 (A.D.), a star in the constellation Taurus blew. Chinese sky watchers reported it to be as bright as Venus, apparent during daylight, and visible for twenty-three days. The remnant of this explosion can be seen today and is called the Crab Nebula. (The Greeks have no record of the supernova.) Experts today have compiled detailed descriptions of supernova explosions that coincide with contemporary X-ray and radio sources. In the Greek-influenced West, the sun and heavens were supposed to be immaculate. But Chinese astronomers saw spots on the sun. The earliest surviving record of a sunspot observation is by the astronomer Kan Te in the fourth century B.C. Kan Te assumed that these spots were eclipses that began at the center of the sun and spread outward. Although he was wrong, he recognized the spots for what they were - solar phenomena. The next documentation of sunspots was in 165 B.C., when it was reported the Chinese character wang appeared in the sun - shaped like a cross with a bar across the top and bottom. It is accepted as the world's earliest precisely dated sunspot. The West's earliest reference to sunspots is Einhard's Life of Charlemagne, around A.D. 807. Joseph Needham found 112 instances of sunspots recorded in Chinese histories between 28 B.C. and A.D. 1638. In other Chinese books he found hundreds more notices, "but no one has had time or stamina to collect them into a body," comments sinologist Robert Temple. Nonetheless, the sunspot records constitute the oldest continuous series of such observations. And again, these are of great use to modern astronomers. Sunspot cycles, for instance, affect the earth's ionosphere and weather (magnetic storms are related to sunspots). Analyzing available records, Japanese astronomer Shigeru Kanda reports he has detected a 975-year sunspot cycle. If so, it may have significant implications for weather cycles. The Chinese were also careful observers of comets. They computed the approximate orbits of about forty comet trajectories with such precision that many of their trajectories could be drawn on star charts simply from reading ancient texts. They were interested in the precise position and direction of the tail of each comet. In the year 240 B.C., astronomers officially documented the appearance of a comet today known as Halley's. Another comet recorded in 467 B.C. is also thought to be Halley's. In the 600s A.D., they observed that comets shine by reflected light like the moon. They noted that comet tails always pointed away from the sun, suggesting this phenomenon was the result of a solar "energy." Today it's known that this cometic tail direction is caused by the force of "solar wind," the sun's radiation. It wasn't much of a stretch, says Temple, for the Chinese to formulate the idea of solar wind. It is congenial with their cosmological assumptions, Chinese literature being filled with references to the ch'i of the sun's radiation. Ch'i, translated as something like the "emanative or radiative force," comes from the sun. To Chinese astronomers it would have been obvious that the sun's ch'i was strong enough to blow the tails of comets as if in a strong wind. The Chinese conceived of space as being full of strong forces. As a consequence of the emperor's divine connection with the cosmos, it became traditional after important changes of rulership, and always after a switch to a new dynasty, for a fresh calendar to be drawn up. This custom was well established by Han times (206 B.C. to A.D. 220) and led to some forty new calendars made up between early Han and the beginning of the Ming dynasty in 1368. According to the theory of monarchy, the ruling dynasty remained fit to rule because of the accord the emperor maintained with the heavenly order. His special status in the order of nature allowed him to maintain a parallel order in the political realm, for the state was a microcosm. If the emperor lacked virtue or was careless in his duties, disorderly phenomena would appear in the sky as a warning of potential political disaster. Thus astronomers had to incorporate as many phenomena as possible in a "correct" calendar. The calendar, issued in the emperor's name, became part of the trappings of power that demonstrated his dynasty's right to rule, a function, writes sinologist Nathan Sivin, "not entirely different from that of economic indicators in a modern nation." The importance of astronomical observing in this world of extreme politics, then, made secrecy absolutely necessary. Because the data could be easily manipulated, it could be dangerous in the hands of someone trying to undermine the current dynasty. It was therefore state policy that the proper place to do astronomy was the imperial court. In certain periods it was illegal to do it elsewhere. With this information virtually classified as top secret, the astronomer became a high-level administrative functionary in a country that developed the most elaborate bureaucracy in the ancient world. The databases resided in a state observatory deep within the bowels of the palace. If not the greatest astronomical mathematicians, the Chinese were the greatest star charters before the Renaissance. Their earliest star chart goes back to at least 2000 B.C., to a carving on a cliff at Jiangjunya in Jiangsu Province. The carving contains many stars, as well as human and animal heads. There are disks indicating the sun in seasonal positions and where a number of bright stars and the moon appear over the seasons. This bright region is recognizable as the Milky Way by its position and appearance; the Milky Way displays gaps and divisions that are depicted on the carving. China, being in the Northern Hemisphere, fixed itself on the northern circumpolar stars, both for orientation and to express its concept of divine rulership. The circumpolar stars in the higher latitudes are raised quite high in the sky as they rotate about the pole, so the fixity of the polar axis became an apt metaphor for the divine right of emperors. The pivot point about which this rotation occurs is known as the north celestial pole. The emperors were clever to adopt the stars of the north, such as Cassiopeia and Cepheus. These stars are located near the celestial pole, so that in the temperate latitudes of most of China they are visible eternally in the sky, never hidden by the horizon. The first catalogs of star positions appear to have been drawn up by Shi Shen, Gan De, and Wu Xian, the earliest notable astronomer in China, who worked between 370 and 270 B.C., two centuries before Hipparchus. Together their lists enumerated 1,464 stars grouped into 284 constellations. (The West made bigger groups, with only 88 constellations.) In A.D. 310, during the Western Chin dynasty (A.D. 265-317), this early work was collated by the astronomer royal Qian Luozhi, who cast a bronze celestial globe with the stars on it colored in red, black, and white to distinguish the listings of the three astronomers. As early as the Han dynasty, astronomers prepared star charts. Carvings and reliefs show individual constellations or asterisms depicted as dots or small circles connected by lines to delineate the constellation itself. This ball-and-link convention did not appear in the West until the late nineteenth century. Star maps need a means of specifying positions of heavenly bodies with reference to one another. The science of mapmaking took a leap forward in the second century B.C. when Chang Heng invented what's now called quantitative cartography. Chang, the inventor of the seismograph and a leading scientist, applied a grid system to maps so that positions, distances, and itineraries could be calculated and analyzed. Chang Heng's own works are lost, although an official history of the Han dynasty stated, "He cast a network of coordinates about heaven and earth, and reckoned on the basis of it." Copies of these maps were never made, since the information on them was too dangerous to risk its falling into the wrong hands. Meanwhile, in Europe, mapmaking had degenerated under the influence of religion, says Robert Temple, "to a point scarcely credible." Drawing actual charts of the sky means finding a way to depict positions as if one is drawing a map. Preparing maps also involves the problem of mapping the curved surface of the celestial sphere on a flat surface, just as mapping the near-spherical surface of the earth requires the use of map projection. This is made more difficult if the sky is seen as a dome curving above one's head. In both China and the West, projection goes back a long way for mapping the earth. But for mapping the stars, Chang Heng was first, drawing up in Han times a chart that was a "Mercator" projection. Mercator projection was "invented" in Europe by the Flemish mathematician and geographer Gerhard Kremer, a.k.a. Gerardus Mercator, and first published in 1568. But this projection system had been used by the Chinese centuries before Mercator. The projection works by means of a cylinder. If one inserts a transparent globe of the earth (or other celestial sphere) in the center of a hollow cylinder and turns on a light inside the globe, the features of the sphere's surface will be thrown, or projected, onto this cylinder, and will reflect a certain distortion. The higher up and lower down from the sphere's center, or equator, the more the features are distorted. Virtually useless for land travel, this projection has the odd property that a navigational course drawn on it will come out as a straight line, whereas with other maps such courses are arcs. The oldest surviving projection chart depicting the whole of the visible sky is painted on paper and now resides in the British Library. Dating from about A.D. 940, it comes from Dunhuang in Gansu Province and gives a flat representation of Qian Luozhi's (the astronomer royal's) tricolored chart, working from his celestial globe. It presents the celestial globe as projected onto a surface by the cylindrical projection technique, displaying over 1,350 stars in thirteen sections. One section is a planisphere - that is, in a kind of Mercator projection it depicts the circle of the sphere on a flat map centered on the north pole. The remaining twelve are flat maps centered on the celestial equator. Continue... Excerpted from Lost Discoveries by Dick Teresi Copyright © 2002 by Dick Teresi Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.