Astronomy and Cosmology: Western and Non-Western Cultural Practices in Ancient Astronomy
Astronomy and Cosmology: Western and Non-Western Cultural Practices in Ancient Astronomy
In the ancient world, astronomy was important for precise timekeeping, religious ceremonies, and agricultural management. The movement of the sun across the sky determined the seasons, while the lunar cycle of 28 days provided convenient divisions of the year—12 months, based on monath, the Old English word for moon. The rising and setting of constellations and stars also provided annual markers, as did solar and lunar equinoxes; ancient temples often marked their positions in the sky. The “wandering” planets, which seem to loop irregularly across the sky in a retrograde motion, suggested to ancient peoples that they were deities. Predicting their movements seemed a means to predict divine action, leading to what we now know as the pseudoscience of astrology.
The precise origins of astronomy are unknown, but it is likely that star observations were first made in ancient Vedic India around 4000 BC. Stone circles that indicated astronomical observation at sites like Stonehenge were built in the Bronze Age (3000–1800 BC). Between 3000 and 2000 BC in Babylonia (Mesopotamia), an ancient kingdom between the Tigris and Euphrates Rivers (in what is now Iraq), astronomers created what we know now as the zodiac. The Chinese also began to make detailed astronomical observations and star charts at approximately the same time. From the sixth century BC until the first century AD, the Greeks developed astronomy into the basic form we recognize today.
Historical Background and Scientific Foundations
Ancient Temples: Stonehenge and Anasazi Monuments
Some ancient astronomical sites may have been viewed as “axis mundi,” a term coined by the Romanian-born philosopher Mircea Eliade (1907–1986) to indicate a point at which sky and earth are thought to meet; at these places the heavens are often reflected in man-made structures. A temple-observatory, for example, is a microcosm that reflects the macrocosm of the universe.
By analyzing cremation remains found at Stonehenge in Salisbury, England, Eliade speculated that the
megalithic complex might have been used for ancestor worship. Because the sun at summer solstice shines directly though the center of the complex over the heel stone, a large menhir about 256 feet (78 m) to the northeast from the center of the Stonehenge, the structure itself may have suggested themes of soul [sol] resurrection via solar astronomy. Other archeoastronomers have posited that the presence of postholes—called Aubrey holes after William Aubrey, the seventeenth-century antiquarian who discovered them—indicate that the structure was a lunar calendar in which users tracked the cycle of the moon by moving a marker two holes each day, completing a complete circuit in 28 days. The ultimate verdict on Stonehenge's true purpose, however, is still undecided.
Later temples, however, demonstrate Eliade's idea of the axis mundi more clearly. In AD 500, Native Americans who lived in the four corners region of what are now Utah, Colorado, Arizona, and New Mexico began to develop a settled agricultural civilization. Because the climate was not particularly arable and rainfall was scarce, it was necessary to observe the weather and seasons keenly to ensure agricultural success.
The Anasazi people built a major village complex in Chaco Canyon in northern New Mexico, orienting most buildings to the sun and the moon. There is also a spiral petroglyph or rock painting aligned with carefully constructed rock slabs; each summer solstice a sun dagger of light pierces the spiral, and similar sun daggers mark the winter solstice and the equinoxes. A kiva complex (round semisubterranean features used for religious ceremonies) in Pueblo Bonito, the canyon's main village, has a series of wall niches that the sun strikes on significant astronomical days.
In Central and South America, the Mayan and Incan civilizations developed sophisticated solar observatories in the form of stepped pyramids that integrated astronomical observation with religious practice. The Mayans were particularly interested in the twice-yearly Zenial passages, when the sun crossed over their latitudes at an altitude of 90 degrees without casting a shadow. These passages are only observable in the tropics before and after the summer solstice. The Mayans also knew of the number zero and kept detailed solar calendars.
Astronomy in the East—Ancient India and China
The study of astronomy in ancient India was called jyotihsastra, or the “science of heavenly bodies.” An examination of Vedic literature reveals that the earliest stages of astronomical study in India were devoted to fixing dates for sacrificial rituals, and that they developed a 12-month solar year with 366 days and 28-day lunar months. Calendrical inaccuracy required the addition of one day every 64 months to preserve the relationship between ritual dates and the lunar phases. This insertion of extra time into calendars to make them more accurate is called intercalation.
The lunar cycle was particularly important to the ancient Indians, and they divided its path into 28 equal parts called nakshatras; the moon passed through one a day as it traveled its monthly orbit. The nakshatras also indicated the position of the moon relative to the sun and other stars and were important for marking the seasons as well as astrology. Before the introduction of sun-based Greek astronomy and astrology, each nakshatra was assigned a deity and worshipped.
In about the third century BC, ancient Sanskrit texts reveal that Hindus also began to worship the planets or grahas as gods, tying their appearance in the sky to seasonal events. The Arthas´āstra, for example, calls Jupiter and Venus by their god-names of Brhaspati and Sukra and claims “From the sun (is known) the successful sprouting of seeds, from Jupiter the formation of
stalks in the crops, from Venus rain.” Northern Indians also linked the disappearance of the constellation Hydra from the night sky to the onset of the monsoon rains, an observation made in 4000 BC.
Like Vedic astronomy, the Chinese were concerned with calendar making and star observation, but their activity was more centrally regulated by the state. The emperor was considered responsible for the harmony of all things in the heavens and on earth, so an accurate calendar and record of celestial occurrences was a matter of imperial prestige.
The ancient Chinese calendar was primarily lunar, each new month beginning with a new moon, and the new month was publicly announced to citizens and to the appropriate gods, whereupon an animal sacrifice would be made. But a lunar month of 28 days eventually becomes out of sync with the solar year, and, like the Vedic Indians, the Chinese used intercalation. The Chinese solution was to erect a gnomon or post, watching the length of the shadows it cast every day at noon. As the winter grew deeper and the days became shorter, the shadow grew longer at noon, until it reached its longest point at winter solstice. The Chinese then added an extra month whenever the longest noon shadow had not occurred before the end of their twelfth lunar month. In this manner, they could begin the year after the winter solstice, keeping the lunar months at approximately the same time in the solar year. In the fourth century BC, the Chinese began to observe the planets carefully, concentrating on Jupiter's retrograde motion to further reform their calendar and accurately describe the synodic periods of Venus and Saturn.
Chinese astronomy's state sponsorship meant that imperial bureaucrats produced detailed records of heavenly phenomena such as solar and lunar eclipses, comets, supernovae, sunspots, and meteors. In 1300 BC, the Chinese recorded the appearance of a supernova, a record used by modern astronomers to correlate ancient novas with the remnants detected today by radio astronomy. Chinese records of sunspots have also helped present-day astronomers study variations in solar activity.
The Chinese were also some of the first to record and predict eclipses, primarily in the service of astrology. By AD 120, an astronomer named Chang Hang realized correctly that when the sun and moon were opposite one another on the celestial sphere, Earth cut off the sun's illumination from the moon. Unfortunately, the Chinese still conceived of Earth as a flat plate, which
IN CONTEXT: ARCHEOASTRONOMY FOCUSES ON STARS, SYMBOLS, AND METAPHORS
Archaeoastronomy is the study of past cultures' beliefs about the sky and how those beliefs affected their lives. It establishes that most pre-scientific peoples developed a cosmology (an explanation of the universe) that explained human existence as seamlessly interwoven into the workings of the universe. This relationship of the part to the whole was usually expressed through symbols and metaphors. A simple, almost universal cosmological principle was captured in the idea of mirroring: events and powers in the sky mirrored those on Earth; Earth was but a microcosm of the sky. In virtually all Northern Hemisphere societies, for example, earthly dwellings (the tepee, yurt, or igloo) were seen as particularized representations of the larger dwelling that arched high overhead in the heavens to create the celestial vault that rotated around the Pole Star. An actual pole of rotation, extending from Earth to heaven, was a strong element of native North American cosmology. In Inuit cosmology, the superior plane (the mythological equivalent of the sky) was known as the Land Above. Other cosmologies have figured the universe as an endlessly folded ribbon, with Earth in the centerfold; as a set of nested boxes; or as a series of interlocking spheres.
Pre-scientific societies held the celestial bodies in great reverence, yet were also on an intimate footing with them. Ancient peoples regarded the sky as inhabited by Sky People, deities, departed ancestors, or simply forces. The Sky People or powers were thought to impose order on chaotic human affairs. At the same time, the sky powers could be solicited and manipulated to serve human goals. Their authority could be invoked to justify the actions of a chief priest or ruler. A moon associated with important periods in the agricultural or hunting cycle could be honored to ensure better food supplies. A desire to place the sky powers in the service of the human agenda may have been the impetus that led pre-scientific societies to take up regular observations of the skies—in other words, astronomy.
would have meant that Earth's shadow should have covered the heavens, a difficult contradiction to explain.
Ancient Western Astronomy: the Babylonians and the Greeks
The twin disciplines of astronomy and astrology had a common origin in ancient Babylonia between 3000 and 2000 BC. As the Babylonians needed a detailed lunar calendar to track the rising waters of the Tigris and Euphrates for their floodplain agriculture, they were masters at astronomical observation.
Their pursuit of astrology was purely religious. Although the stars follow a regular course from east to west as the night progresses, the planets do not, seeming to move backward and then forward. This erratic behavior of the wandering planets (Mercury, Venus, Mars, Jupiter, and Saturn) through the narrow band of the zodiac led the Babylonians to believe that the planets were gods possessed of their own animate forces. In approximately 500 BC Babylonian priests identified the constellations that marked the zodiacal band into twelve segments of thirty degrees each, producing the astrological signs. For the Babylonians, the zodiac was not only a way to chart the motions of the sun, moon, and planets, but a way to make astrological predictions as well. The first known cuneiform horoscope was cast in 410 BC.
Babylonian astrology and astronomy traveled to the Greeks via trade and Alexander the Great's (356–323 BC) conquests. Alexander's victories and his efforts to “Hellenize” his empire melded Greek, Babylonian, and Egyptian cultures in the Mediterranean world. As a result, the Greeks adopted Babylonian names for constellations and began to cast horoscopes, predict eclipses, and name planets after deities. The line between astrology and astronomy was indistinguishable in ancient Greece, but, unlike in Babylonia, both practices were seen as branches of mathematics.
In the fifth century BC the ancient philosophical sect of Pythagoras (580–500 BC) thought that the planets, sun, moon, and stars revolved around Earth in concentric circles, each fastened to a crystalline sphere or wheel. The daily rising and setting of the stars suggested that motions in the heavens were uniform, circular, and eternal. The Pythagoreans believed that mathematics was the key to understanding this reality.
Though the geocentric or Earth-centered model was the predominant cosmological scheme in the Greek world, other philosophers such as Heraclides Ponticus (387–312 BC) proposed a system in which the planets revolved around the sun, and the sun with all its planets revolved around Earth. The astronomer Aristarchus of Samos (310–230 BC) not only improved estimates of the length of the solar year, but was the first to propose a totally heliocentric universe. Finally, by using geometry, developed by Euclid (born c.300 BC), the ancient Greeks realized Earth was a sphere and correctly measured its circumference by the second century BC.
Despite these innovations, an Earth-centered universe predominated in ancient Greek astronomy, and this geocentric system was supported by the philosophical schools of Plato (428–348) and Aristotle (384–322). The astronomer Ptolemy (AD c.90–c.168) in his astronomical work, the Mathematike Syntaxis (Mathematical arrangement) known in the West by a corruption of its Arabic title, the Almagest, provided an accurate set of naked-eye star observations based on the premise of an Earth-centered cosmological model, as well as geometrical
constructions that accounted for the retrograde motion of the planets in the sky. Ptolemy's work dominated astronomy until the publication of Nicolaus Copernicus' (1473–1543) De revolutionibus orbium coelestium libri vi (Six books concerning the revolutions of the heavenly orbs), in 1543.
Modern Cultural Connections
Ancient astronomers not only created solar and lunar calendars (which are the basis of our modern calendar), but also formulated the pseudoscientific yet pervasive discipline of astrology. Our constellations, planetary names, and formation of the zodiac are due to these ancient sky watchers. Imperial Chinese stellar observations still inform modern astronomers of the history of our universe, while the ancient Greeks developed the mathematical tools that have enabled us to measure the dimensions of the solar system.
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IN CONTEXT: SETI
Ancient astronomy still stirs the imagination with regard to the cosmos, especially toward the possibility of life among the stars. Early tales that animated the heavens with figures common to human experience have gradually evolved to sophisticated and scientific exploration of the stars.
One of the major efforts in the last quarter of the twentieth century was a project termed the Search for Extraterrestrial Intelligence (SETI). SETI is a term that encompasses several different groups and their efforts to seek out intelligent extraterrestrial life. The driving force behind these groups is the ancient human desire to understand the origin and distribution of life throughout the universe. As technology progresses, SETI efforts have moved from the study of extraterrestrial rocks and meteors towards scanning the skies for a variety of signal types. For decades, scientists have listened for an elusive radio signal that would confirm the existence of extraterrestrial life.
Cornell University professor Frank Drake (1930–) founded the first SETI program in late 1959. Drake reinforced his idea of scanning the skies with his famous Drake Equation. The Drake Equation predicts the abundance of intelligent life within a certain galaxy:
(N = N * f(p) * n(e) * f(l) * f(i) * f(c) * f(L))
On August 15, 1977, astronomer Jerry Ehman was going through the computer printouts of an earlier SETI-like project run by Ohio State University that was dubbed, “Big Ear,” when he discovered the reception of what remained throughout the twentieth century as the best candidate for a signal that might have as its origin an extraterrestrial intelligence. Excited, Ehman scribbled, “WOW!” on the printout and forever after the signal became known as the WOW! signal.
Despite repeated attempts to reacquire the signal, the fact that the signal was never again recorded makes many astronomers, including Ehman, skeptical about the origins of the WOW!signal. If it were an intentional signal, astronomers argue, the sending civilization would repeat it—or something like it—many times. Some scientists explain the WOW! signal as a mere reflection of a signal from Earth off of a satellite.
Although government funding fluctuates, various SETI projects continue, sometimes as private research efforts. In May 1999, the University of California at Berkeley launched one of the earliest global distributive computing projects in the world and one of the most widespread SETI efforts in history. Berkeley scientists with the [email protected] project collect data from the Arecibo Radio Observatory in Puerto Rico. The data are then divided into work units and sent out to the personal computers of volunteers throughout the world. These personal computers scan the data for candidate signals. The project is ongoing, as of early 2008. The popularity of the project demonstrates that the primal human wonder and need to understand the place of humanity among the stars still exists.
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Anna Marie Eleanor Roos