Star Walk of the Orient--Chinese Astronomy

Everyone knows the story of the Star of Bethlehem, in which the Magi are guided by a star on a long journey to witness the birth of Jesus. But was there really a Star of Bethlehem? If so, which star would it have been?

Huang Yi-nung, a history professor at National Tsing Hua University, has made a career of studying ancient Chinese astronomical records, and found that China was the only place in the world where accurate astronomical records were being kept around the birth of Christ. Chinese records show two heavenly objects that appeared unexpectedly around that time.

One of these was a comet that appeared in the vicinity of Alpha and Beta Capricorni in March of 5 BC. Then another comet appeared in April of 4 BC near Altair in the constellation Aquila. The comet of 5 BC had a tail, while the one that came a year later did not. Professor Huang notes that the comet of 5 BC was visible about an hour before sunrise some 30 to 40 degrees above the horizon to the south-southeast. This matches the description of the unusual star that the Magi reportedly saw in the east. This comet remained visible to the naked eye for only about 70 days, however, which would mean that the Magi must have been looking at some other comet as they made their way from Jerusalem to Bethlehem. That would put the birth of Jesus at 4 BC, which dovetails nicely with the conclusion of Biblical scholars concerning the year of Christ's birth. This again indicates the depth and accuracy of ancient astronomical records.

Comets and shooting stars

At a time when specialized terminology for describing stars did not yet exist in the West, the monumental Records of the Grand Historiographer, authored by Sima Qian during the Han dynasty, included a chapter listing more than 1000 stars visible to the naked eye and identifying each one by name. When the ancient tomb of the Marquis of Zeng was unearthed at Mawangdui (Hunan Province) in the 1970s, archeologists discovered drawings of 29 types of comets. The tails were depicted in many forms: double, hooked, perfectly straight, etc. These cartoon-like sketches depicted phenomena that modern-day astronomers recognize instantly. Says Sun Wei-hsin, a professor of astronomy at National Central University, "The long, straight, narrow tail is an ion tail, while the hooked tail is a dust tail." Professor Sun is impressed by the skills of the ancient colleague who executed the sketches of Mawangdui. He explains that an electrically charged ion tail trails directly behind the comet, while a dust tail is pulled toward the sun by the sun's gravitational field.

Sustained observation and classification of comets is not all the Chinese are noted for. Our forebears were also the first in recorded history to observe Halley's comet, the explosion of a supernova, and sunspots. Sunspots are mentioned at least 120 times in China's official histories.

Halley's comet has had a greater impact than any other upon astronomy. The period of its orbit was discovered first, and sightings of it can be traced with certainty to more than 2000 years ago. It is mainly Chinese records that allow us to do so. The earliest known sighting of Halley's comet was recorded by Ban Gu in his History of the Western Han Dynasty, and detailed records of later sightings can be found at 76-year intervals for every subsequent approach of the comet.

Although much scientific and technical terminology was first introduced to China via translations from Western languages, this is less true in the field of astronomy. Many technical terms still used today, including tian wen ("astronomy"), are not translations. Other examples include hui xing ("comet"), yun shi (meteorite), and liu xing (meteor). The term tian wen literally means "the pattern of the skies," and refers to the systematic study of heavenly events-the waxing and waning of the moon, sunspot activity, planetary movements, the type and color of comets, and the shape and splitting of sunspots. Ancient Chinese astronomers were especially interested in what they called "guest stars," i.e. a supernova explosion or any other one-off event that did not fit the regular pattern. They carefully noted dates, duration, position, and brightness. Systematic records of all of these observations go back a very long time.

Unexpected guests

In Science and Civilization in China, British scholar Joseph Needham notes that apart from the Babylonians, most of whose records have been lost, in the ancient world the Chinese were the most persevering and accurate observers of the skies prior to the Arabs. Chinese records of the appearance of novas and supernovas are a striking example.

At dawn on July 4, 1054 AD, an extremely bright reddish star appeared in the eastern sky. Visible even during the daytime, its appearance electrified all of China. Astronomers at the imperial observatory worked day and night making careful and continual observations until the object finally disappeared from sight 643 days later in April of 1056. The new star was recorded to be close to the ecliptic, in the vicinity of the star Zeta Tauri. The supernova has long been assumed to be the source of the Crab Nebula and its associated pulsar, although this view has been challenged in recent years.

A nova or supernova is produced when an aging star explodes and flashes up at a luminosity of several billion times that of the sun. In addition to releasing X-rays and high-energy cosmic rays, such an event can also generate nebulas, quasars, and pulsars. These phenomena are important subjects of research on the evolution of heavenly bodies.

When these exploding masses suddenly intruded upon the otherwise orderly and predictable pattern of the skies, early Chinese astronomers called them "guest stars." Counting up the guest stars mentioned in ancient records, modern researchers have found that after one discounts comets, ancient Chinese astronomers observed nearly 90 of these brilliant events. It is interesting to note that the stars which explode into novas and supernovas are, before the explosions, relatively dim. Says Huang Yi-nung, who specialized in supernovas when he studied astronomy in the United States, "We haven't seen a supernova in the Milky Way in 400 years. The ancient astronomers were luckier than us." To do his research, Huang had to burrow into so many stacks of ancient historical records that he finally decided to change course and become a historian.

Every man an astronomer

Back in the days when instruments were simple and people looked to the skies with a mixture of awe and fear, Chinese astronomers distinguished themselves by their ability to observe the stars in a systematic manner not matched anywhere else. Why was this so?

Observation of the skies was necessary for devising calendars. Ancient agrarian peoples observed the heavens very closely to ensure properly timed planting and good harvests. They tracked the movements of the sun, moon, and stars, and pinpointed the changing of the seasons. The sun and moon have always had an especially big impact on daily lives. Homes are oriented to achieve maximum comfort in both winter and summer, as well as optimum light and ventilation.

When the national capital was moved during the Zhou dynasty (1121-249 BC) to Luoyi (modern-day Luoyang), the Duke of Zhou built a device there to help determine the seasons and the directions. Astronomy was a part of everyday life in those ancient times, for city lights did not exist and anyone could see a multitude of stars just by looking up. The late-Ming scholar Gu Yanwu once wrote, "In the Xia, Shang, and Zhou dynasties, everyone was an astronomer. Every tiller of the fields was familiar with Antares. Each farm woman spoke knowledgeably of Scorpius." In fact, this was no exaggeration. To describe two people fated never to cross paths, poets of the Tang and Song dynasties were fond of the phrase "as far apart as Can and Shang" (two stars in opposite parts of the sky that never come into view at the same time). There are countless other expressions in classical Chinese poetry that similarly reflect a deep familiarity with the heavens.

According to Huang Yi-nung, "Ancient astronomy was not just a physical science. It was also a social science." In his view, astronomy gave the Chinese people a set of coordinates by which to construct a view of the space and time in which they lived. In astronomy people found a medium for close interaction with nature. The idea of a unity between the heavens and human beings enabled interaction between the two, and laid the foundation for a cosmological view of the entire universe as one indivisible whole.

Humans have always looked with awe and fear upon that which we cannot understand, which is why our forebears were so careful to pick the most auspicious times for events, and the most propitious orientations for homes and other important things. A class of specialists arose who were adept at interpreting messages from above, and the Han dynasty years brought new depth to the set of beliefs associated with the idea of man and the stars impinging upon the course of each other's events.

In the reign of emperor Han Wu Di (141-87 BC), Dong Zhongshu tried to use catastrophes to hold the emperor in check and prevent excessive concentration of political power in his hands. He argued that unusual heavenly events portended major changes in the course of human affairs, and championed the idea that one could predict the future by observing the stars. Astrology became increasingly systematized, and the names of stars reflected political realities on earth.

Astronomy thus played a role in larger society as well as in science. China's rulers have supported astronomy since ancient times, and departments concerned with matters of astronomy are among the very earliest scientific research organs in the history of Chinese bureaucracy. An imperial observatory was established in 2000 BC, and its Qin dynasty successor in the 3rd century BC employed over 300 people. Astronomy has always been highly valued, and dynastic changes never resulted in a cutoff of support.

Establishing systems and organizations is a very important part of scientific research, and this is what propelled Chinese astronomy to such a high level of achievement. Precision instruments and algebra enabled scientists to calculate planetary orbits and the timing and position of celestial events with astounding accuracy. Every period of Chinese history has produced many outstanding astronomers.

Astronomer extraordinaire

In the lobby of the Taipei Astronomical Museum, a bronze statue of the great astronomer Zhang Heng stands beneath an imposing model of the solar system. As Grand Historian of the Latter Han dynasty, Zhang Heng was in charge of astronomic research, keeping the calendar, and monitoring the weather and earthquakes. He tracked the movements of Venus, Jupiter, Mercury, Mars, and Saturn for many years running, and accurately described their orbits. From his observatory in Luoyang he recorded 2500 stars, thus covering nearly all the 2500-3000 stars that are visible at one time to the naked eye (stars of 6th magnitude and brighter). While his contemporaries were reacting to lunar eclipses by beating on gongs to scare away the "celestial hound" that they believed was trying to swallow the moon, Zhang Heng was writing that lunar eclipses occur when a full moon enters the earth's shadow. He also wrote that the moonlight is only reflected sunlight, and that lunar phases are the result of the moon's reflection of the sunlight from different angles.

Zhang designed instruments, carried out experiments, and made observations to support his theories. He invented a type of astrolabe, with graduated rings and a sighting tube, to measure the positions of heavenly bodies. He set the standard for excellence in astronomy, and has been followed by a long line of brilliant successors over the centuries, including Yi Xing, Su Song, Guo Shoujing, and Zu Chongzhi. The precision and complexity of ancient Chinese astronomical instruments is widely acknowledged today.

Joseph Needham writes that the water-driven astronomical clock invented during the Song dynasty was a major milestone for the world in the fields of both astronomy and timekeeping. It had a removable wooden roof, thus making it the forerunner of today's domed observatories. The astrolabe within the structure completed one rotation in a day, and in this sense it was also the forerunner of the timepiece-driven tracking mechanisms used in modern observatories. The water-driven clock employed a ratchet assembly, a key element of mechanical timepieces, which thus made the astronomic clock a forerunner of modern clocks as well.

Huang Yi-nung asserts, "Our astronomers were first-rate observers, and they had an encyclopedic mastery of the natural sciences, social sciences, and humanities." Huang notes that astronomy is a comprehensive science that is intimately connected with our lives and, as such, is not separate from nature as a whole. Zhang Heng is also noted for inventing the world's first seismic detector, and was an accomplished painter and writer. Astrological beliefs were part and parcel of the science of astronomy in those days, and Zhang Heng was naturally an astrologer, but unlike those of today, notes Professor Huang bluntly, "All ancient astrologers were expert observers of the heavens. Today's astrologers don't know anything about the stars."

For the intellectuals of antiquity, the quest for intimate knowledge of the stars above and the earth below was not a matter of mere lip service. The famed Grand Historian Sima Qian was the scion of a long line of astronomers. Qu Yuan, the great poet from the 4th century BC who is perhaps better known today as the inspiration for southern China's annual Dragon Boat Races, is also highly regarded by astronomers for his observations on the structure and origin of the universe. Song dynasty scholars typically owned astronomical instruments, and students had to study the subject. In The Complete Works of Zhu Xi, it is mentioned that the great scholar Zhu used the astrolabe in his home to teach his students the difference between the North Pole and the North Star.

Species memory?

"It is hard to imagine how long it must have taken to build up the body of knowledge needed to execute the comet sketches found in the Han tomb at Mawangdui," says Professor Sun Wei-hsin, who notes that the astronomical records compiled by the Chinese over the centuries have been very helpful in later attempts to understand the mysteries of the universe. Cosmic time and space are so vast that no individual ever gets the opportunity to see most celestial events in the course of a lifetime. Scientists who want to achieve significant breakthroughs had better be prepared to spend time reviewing records dating back to antiquity.

Halley's comet is a case in point. By comparing ancient records against observations made when Halley's comet made its 35th recorded fly-by in 1986, we can see that the comet has not changed much in 2600 years. It still has about the same mass as before, an important bit of information to scientists researching the history of the solar system.

The supernova observed by Song-dynasty astronomers in 1054 remained visible even during the daylight hours for 23 days. From the records taken at that time we can calculate the brightness of the exploding star, and we can use its brightness curve to figure out whether the progenitor was a single star or binary system. Says Professor Sun, "Chinese records are without dispute one of the great treasures of astronomical science." Unfortunately, Chinese terminology poses a barrier to modern astronomers, most of whom are Westerners. That is why Professor Huang decided to switch course and tackle ancient Chinese astronomy.

Celestial seasons

For people today, the interest of ancient Chinese astronomical records lies not only in their value to modern astronomy, but also in the historical and cultural insights they provide. In recent years, Huang Yi-nung's research into Chinese astronomical records have given us a new perspective on history.

Water can float your boat, but the waves can sink it. Although Chinese astronomical observations have helped us understand nature, the politically important role that astronomy once played often impinged upon the integrity of the science. Records were faked on many occasions in ancient China. The planetary alignments and conjunctions of Mars and Antares that have gotten people so excited recently have been used since time immemorial by political figures casting about for ways to attack their enemies.

The silk scrolls unearthed at Mawangdui in 1973 include a lot of information on planetary alignments compiled by ancient researchers. The ancients had determined, for example, a synodic period of 584.4 days for Venus, 377 days for Saturn, and 395.4 for Jupiter. Modern astronomers have confirmed that these calculations were very close to the mark. During the reign of the emperor Han Gao Zu, Chinese astronomers recorded an alignment of Venus, Jupiter, Mercury, Mars, and Saturn within a single 30-degree arc of the sky. This type of planetary alignment, known in Chinese as a "five-star string of pearls," was followed during the same emperor's reign by a Grand Alignment, featuring the same five planets plus the sun, moon, and earth.

A five-star planetary alignment can last three to five days, and in Chinese astrology signifies "the appearance of a shining king." Professor Huang calculates that there should have been one such alignment during the regency of Empress Dowager Wei Hou, who was murdered in 710 AD. But there is no record of any such alignment, and he speculates that male-oriented dynastic historians may have considered a woman's regency an aberration, and accordingly kept quiet about such an auspicious sign occurring while the empress dowager was in power.

Unlike a planetary alignment, the occasional occurrence of ying huo shou xin ("Mars meets up with the constellation Xin) was considered a very inauspicious sign for the emperor. Ying huo was an ancient name for Mars, but the term also meant "confusion and tumult." Mars was usually regarded as a harbinger of rebellion, lawlessness, disease, and death. At most times Mars moves eastward with respect to the background stars. During a retrograde loop, the planet will move backwards in that respect, or retrograde. Every once in a while such a retrograde loop occurs in the constellation Xin, one of the 28 ancient Chinese constellations and home to the star Antares, which the ancient Chinese considered the heavenly counterpart to the emperor.

Checking on such conjunctions of Mars and Antares recorded by ancient Chinese astronomers, Huang was surprised to find over ten falsely reported instances. Why would this have happened? The emperor Han Cheng Di offers a good illustration of how these shenanigans came about. The sex-hungry ruler replaced his empress with the beautiful concubine Zhao Feiyan and allowed relatives of his new consort to gain control over the levers of political power. Amidst deadly intrigue in the court of the profligate emperor, someone cooked up a false report in 7 BC of a conjunction of Mars and Antares. The emperor took the bait and, feeling threatened by the ominous convergence, accused the minister Zhai Fangjin of bringing on the dire straits though inept government. The minister was forced to commit suicide to ward off the disaster that the heavens supposedly portended.

In view of astronomy's potential as a tool of political intrigue, in the Tang and Song dynasties China's rulers made it a crime to leak astronomical knowledge to the general populace, in a bid to prevent commoners from telling the fortunes of the imperial house. Astrology books were banned, the position of imperial astronomer became hereditary, and the appointment gradually lost importance. After Western science began advancing rapidly during the Ming dynasty and missionaries introduced the Western calendar, Chinese astronomical records slowly sank into oblivion.

Algebra no match for geometry?

Kiyoshi Yabuuchi, a Japanese historian of astronomy, has written that although pre-modern Chinese astronomers compiled a wealth of data, they took scant advantage of it to develop scientific theory. Instead, they stuck to the popular belief in the interdependence of human and celestial events. Modern scientists generally feel that Chinese astronomy never developed into a true science.

The decline of Chinese astronomy has been a hot topic among scholars with a special interest in the history of astronomy. In addition to the baggage of a vulgarized form of the belief in a cause-and-effect relationship between the heavens and human affairs, mainland Chinese scholar Xi Zezong further notes that Chinese geometry was no match for that of ancient Greece. Even though Chinese scholars had a highly developed algebra that enabled them to make precise calculations of planetary positions and work out an extremely reliable calendar, says Xi, Chinese planar geometry never addressed the question of angles. With right triangles, for example, Chinese geometricians only concerned themselves with the relationships between the lengths of the different sides of the triangle while making no attempt to measure the angles. The Greeks, by contrast, made 3-D models, modified them to explain their empirical observations, and then used the models to calculate future positions of celestial bodies. As they made new observations they would revise their model to account for any discrepancies, repeating the process over and over again in pursuit of perfection. Says Xi, "These geometric models helped the Greeks inquire into the physical layout of the universe and the principles behind the movements of heavenly bodies. Just using traditional Chinese algebra, it would have been very difficult to arrive at the Copernican model of a sun-centered solar system, or to work out Kepler's laws of planetary motion."

Huang Yi-nung takes a different perspective. He notes that the Copernican model of the solar system was not without flaws, nor was Kepler completely accurate with his geometry-based calculations of the distances between the planetary orbits. "From the perspective of pure math," says Huang, "very precise astronomy can be done with either algebra or geometry. There may only be one correct answer in science, but there are many ways of arriving at it."

According to Liu Chun-tsan, a scholar researching the history of Chinese science, the telescope was the key factor propelling Western astronomy to new heights and overshadowing Chinese astronomy. Because the Chinese sighting tube did not have a curved lens, it did not gather light and allow the viewer to see a long distance. Not unrelated to this shortcoming is the fact that the raw materials for glass are most abundant in deserts. Arabs pioneered glassmaking and later transmitted the technology to Europe, where the telescope was invented in the early 17th century. All of a sudden vast hidden swaths of the universe were before the eyes of Western astronomers, and the idea of supernatural forces working their will and whim upon nature was quickly abandoned. From that point forward, Western astronomy became increasingly scientific.

In fact, in any land and age, the human longing for a sense of security is likely to keep popular belief in astrology alive and kicking. But with the extremely high-powered telescopes that are trained on the skies today, heavenly bodies are no longer veiled in secrecy. One question that Chinese astronomers might do well to address is how to resurrect ancient Chinese astronomy and make it into more than just a quaint source of astro-babble among people wondering which zodiac signs make for a romantic match.