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Equinoxes; Solstitial Alignments. Drombeg; Recumbent Stone Circles; Stone Circles.
References and further reading
Burl, Aubrey.
New Haven: Yale University Press, 2000.
Ruggles, Clive.
Haven: Yale University Press, 1999.
Azimuth means the bearing of a direction—such as that toward a particular point on the horizon from a given place—measured clockwise around from due north. Thus the azimuth of due north is 0°, that of due east is 90°, that of due south 180°, and that of due west 270°. The azimuth of a point one degree to the west of north is 359°. Azimuth is measured in the horizontal plane through the observer. To fully specify the direction of an observed point, one must also specify the vertical angle or
It is possible to specify the position of a star or other object in the sky by its azimuth and altitude, but this will change with time owing to the diurnal motion of the celestial sphere. Even at a given moment, the azimuth and altitude values of a particular star will be different for observers at different places on the earth.
See also:
Compass and Clinometer Surveys; Field Survey; Theodolite Surveys. Altitude; Celestial Sphere; Diurnal Motion.
References and further reading
Aveni, Anthony F.
Ridpath, Ian, ed.
New York: Pi Press, 2004.
Ruggles, Clive.
Haven: Yale University Press, 1999.
The Aztec (also known as the Nahua, or Mexica) empire—the last of the great Mesoamerican civilizations—dominated the highlands of central Mexico at the time of the arrival of Hernando Cortйs in 1519. It had risen to power following a series of military conquests just a century or two earlier and maintained economic control by extracting tributes in the form of foodstuffs and raw materials (as well as personal services) from conquered populations. The Aztec capital of Tenochtitlan, situated at the center of present-day Mexico City on an island approached along three long causeways, had an estimated population of 250,000. The mass sacrifices to their war and sun god Huitzilopochtli, which took place at the great Templo Mayor in the center of the city, are legendary.
The landscape around the Aztec capital is characterized by strings of mountains and towering volcanoes that surround and dominate flat valleys, creating obvious associations between mountains, clouds, rains, fogs, thunderstorms, springs, and rivers. Under the valley floors and mountain slopes are numerous caves created by ancient lava flows. And before time took its toll and the suburbs of Mexico City spread through the landscape, the terrain was also peppered with magnificent human constructions, both the temples of the Aztecs themselves and the conspicuous remains of earlier temples dating back to the Preclassic period (at least as far as the mid-first millennium B.C.E.). This combination created, in the Aztec mind, a vibrant perceived world strewn with the abodes of powerful spirits: mountains were sources of water and rain; caves were entrances to the underworld; and the huge ceremonial center of Teotihuacan with its enormous pyramids, a thousand years old by this time, was itself seen as a magnificent creation of the gods.
Tributes to the gods had to be made in the appropriate place but also at the correct time. One of the most critical actions was to appease Tlaloc, the god of rain and fertility, and persuade him to send water for the year’s maize crop. Petitions to Tlaloc were timed in relation to calendar festivals and often involved the sacrifice of children. Thus on the first day of the month Atlcahualo (in the 365-day calendrical cycle or
Many different calendrically timed rituals such as these, taking place all over the Aztec empire, generated a network of relationships in people’s minds between sacred places in the landscape (particularly mountains), the activities that took place there, and the timing of those activities. Evidence suggests that those perceptions were reinforced both by the positioning of temples in the landscape and by solar alignments deliberately built into those temples. It has been proposed that the Templo Mayor was (at least approximately) aligned upon Cerro Tlaloc on the horizon to the east, that the sun would have risen more or less behind that mountain on the equinox, and that two prominent mountains on the eastern horizon from Cerro Tlaloc itself, across the next valley, aligned with sunrise on two important days when mountain ceremonies were taking place on that peak. More recent work suggests that the later phases of the temple were in fact oriented upon sunset at the feast of Tlacaxipehualiztli, which coincided with the Julian vernal equinox in 1519 and was duly recorded by the chronicler Motolinia. Whatever the details in this case, the combination of ethnohistorical accounts relating to the nature and timing of ceremonies, archaeological evidence of votive offerings at sites such as mountain shrines, and archaeoastronomical data on orientations and alignments makes a convincing case that many relationships such as these were real enough in the Aztec mind.
See also:
Sacred Geographies. Cacaxtla; Horizon Calendars of Central Mexico; Mesoamerican Calendar Round.
References and further reading
Aveni, Anthony F.
Iwaniszewski, Stanis√aw, “Archaeology and Archaeoastronomy of Mount Tlaloc, Mexico: A Reconsideration.”
Ruggles, Clive, and Nicholas Saunders, eds.
, Ivan. “Astronomical Alignments at the Templo Mayor of Tenochtitlan, Mexico.”
———.
Ancient Babylonia occupies a pivotal place in the history of modern scientific astronomy. In great part this is due to the conscientious nature of the astronomical observations that were made there and the meticulous way in which they were recorded for generation after generation. In time, the existence of a huge, cumulative database of past observations made possible the development of mathematically based rules for predicting future events. The Babylonian legacy of careful observation and recording combined with mathematical modeling went on to influence developments in ancient Greece and beyond. The other reason ancient Babylonia is so important to modern historians of astronomy is the fortunate choice of medium on which many of the ancient astronomical observations (along with many other documents) were recorded. The method used was to press wedge-shaped marks into smooth, damp tablets of clay using a stylus. Subsequently, the tablets were dried in the sun or fired in kilns for permanence. Clay tablets do not tend to disintegrate with time like (say) parchments or papyri and are unaffected by subsequent fire, so they frequently survived the looting or destruction of buildings and other cataclysmic events of history. The Babylonian cuneiform script was deciphered in the nineteenth century. In short, many high-quality records have survived, and they can be read.
The ancient city-state of Babylon lay some 90 kilometers (55 miles) south of modern Baghdad. Its power and influence came to cover all of lower (southern) Mesopotamia—the region of modern Iraq between the Tigris and Euphrates rivers down to the Persian Gulf—in the eighteenth century B.C.E., after which it followed a turbulent history under a succession of dynasties until its conquest by the Persians in 539 B.C.E. Subsequently, Babylon became part of greater empires: the Persian until 331 B.C.E., when it was conquered by Alexander the Great; then (after Alexander’s death) the Seleucid Empire; it ultimately fell to the Romans in 63 B.C.E. The latest known cuneiform tablet dates to C.E. 75.
Most of the written evidence that comes down to us is in the form of clay tablets from the Seleucid period from 311 B.C.E. onwards. Those including astronomical data are of various types: astronomical diaries containing nightly observations; records of sightings of astronomical events such as planetary conjunctions and eclipses; and (increasingly with time) almanacs containing predictions of the length of the month, the positions of the planets among the fixed stars, and many other things. These documents demonstrate beautifully how the systematic accumulation of carefully recorded passive observations led in time to the ability to predict using mathematical models. One thing that made this development possible was the Babylonian system for representing numbers: like ours it used a fixed base, but instead of ten, the base was sixty. In other words, each “digit”—itself a set of strokes representing tens and ones—represented a value from zero to fifty-nine, with subsequent digits representing “units,” multiples of sixty, multiples of sixty times sixty, and so on. (The Maya, in contrast, used a base of twenty.)
In the Babylonian calendar, the new day began at sunset and the new month began when the thin crescent moon was first sighted in the evening sky after sunset. Back in the third millennium B.C.E., two calendars seem to have existed in parallename = "note" an “ideal” calendar that was theoretical, with each month containing thirty days, and a common calendar based on actual lunar observations. The first of these calendars is used in early clay tablets that are essentially business documents: this is hardly surprising, since people had to agree on the day something had been signed or a commitment had been made, and this could not be dependent upon the vagaries of whether or not the new crescent moon had been seen (which could be a matter of some dispute, especially if it had been cloudy in certain places at critical times). This civil calendar needed to be the same all over Babylonia and not subject to disputes between different local officials.
Nonetheless, it seems that the actual astronomical calendar (rather than the abstract “ideal” calendar) was used for civil purposes from the second millennium B.C.E. onwards, despite the attendant problems. Gradually, the analysis of accumulated observations of first sightings of the new crescent moon enabled Babylonian astronomers to develop mathematical “rules of thumb” that permitted month lengths to be accurately and reliably predicted. Furthermore, by about the fifth century B.C.E., the nineteen-month (Metonic) intercalation cycle had been discovered and established. It provided a rule whereby the additional (intercalary) months needed to keep the lunar calendar in step with the seasonal (solar) year could be added in a mechanical, deterministic, yet reliable way. Astronomers no longer had to depend upon independent astronomical observations, such as the heliacal rising of Sirius.
One of the most remarkable consequences of the Babylonian astronomers’ attention to detail and the sheer volume of records that they accumulated over many generations was the recognition of the so-called Saros cycle: it described the fact that if a lunar eclipse occurs, others will tend to follow at regular intervals of eighteen years and eleven days for many centuries thereafter. This discovery was no mean feat, since approximately forty different Saros cycles run simultaneously, and the conditions for visibility of any particular eclipse vary considerably—many are completely invisible from any given location on the earth (if they occur during daytime, for example). They simply cannot be revealed by casual observations of lunar eclipses over a few years or even decades, even if clear skies were permanently assured.
In view of its undoubted influence on the development of modern astronomy, it is tempting to view the Babylonian tradition as the birthplace of scientific investigation of the heavens. But this would be highly misleading. The main motivation for the Babylonians’ intense interest in the skies was astrological. Different days in the common calendar were associated with different prognostications, and by the seventh century B.C.E., scholars were advising the Assyrian king of the calendrical omens. A particular concern was the issue of whether the forthcoming month would have twenty-nine or thirty days. Other concerns included the length of day and night, the heliacal events of stars, the positions of the planets, and of course the occurrence of solar and lunar eclipses. One of the most important series of celestially related clay tablets has become known as the
This was not astrology in the sense that celestial configurations were perceived as the direct cause of terrestrial events (although this did become a widespread philosophy from the fourth century B.C.E. onwards in Hellenistic Greece) but rather that they provided portents of events that could then, if necessary, be averted by taking appropriate action. In this, astronomical predictions were used along with a variety of other forms of divination.
Ancient Babylonia was also the birthplace of modern horoscopic astrology, or at least the earliest known example of the belief in the predictive capabilities of charts recording planetary positions at the moment of a person’s birth. (Actually, the horoscopes of modern popular astrology represent a revival of this belief rather than any sort of continuity of tradition.) An important prerequisite was the division of the zodiac (through which the plan-ets move) into twelve regions of equal size. Birth charts began to appear in the second half of the first millennium B.C.E. and represented a move away from the astrologers having to watch the skies passively, waiting for omens to appear, to the more active pursuit (performed on demand) of calculating where the planets would have been among the stars at a particular time. It also represented a shift away from observational astronomy toward intensive mathematics. It is ironic, in view of the way in which modern astrology is seen as the very antithesis of modern science—irrational and unscientific— that this astrological innovation in Babylonian times necessitated making full use of the most up-to-date scientific knowledge and methods that had been developed by this time.
From the late third century B.C.E. onward, two fundamentally different schools of thought emerged for generating predictions from the extensive records of existing observations. These seem to have coexisted throughout the final few centuries of ancient Babylon (until the late first century C.E.), to judge by two types of works—mathematical ephemerides and almanacs known as Goal Year Texts—that were evidently produced in parallel. The ephemerides represent the height of Babylonian scientific achievement, using sophisticated mathematical models to predict phenomena of the moon and planets with remarkable accuracy. The Goal Year Texts, on the other hand— each one a sort of astrological handbook for a given year—seem to represent an independent tradition of prediction based upon repeating cycles that had been discovered by studying the existing diaries of observations (the Saros cycle was one of these).
There is a great deal still to be learned about the nature of astronomical and astrological knowledge in ancient Babylonia and the social context in which it operated. Though about three thousand fragments of clay tablets containing astronomical information are currently known to exist, a huge amount of basic data simply remains unexplored. There are tens of thousands of fragments of clay tablets in the British Museum alone, many tens of thousands more in other museums around the world, and untold quantities still buried under the ground in modern Iraq. Since a sizeable proportion of the clay tablets that have been studied contain astronomical information, there is every reason to expect the same to be true in the future. And while many of the museum specimens are of unknown provenance, only eventually having found their way into the public domain after progressing along tortuous routes, some of those still waiting to be discovered may be excavated in a context that will yield valuable archaeological information about their broader function and significance.
See also:
Astrology; Eclipse Records and the Earth’s Rotation; Lunar and Luni-Solar Calendars; Lunar Eclipses; Mithraism; Solar Eclipses.
Fiskerton; Maya Long Count. Heliacal Rise; Zodiacs.
References and further reading
Aaboe, Asger.
Neugebauer, Otto.
Rochberg, Francesca.
Steele, John.
British Museum Press, 1996.
Ballochroy is one of many hundreds of small megalithic monuments found in western Britain. The casual visitor is unlikely to be greatly impressed at the sight of it: a row of three standing stones, one broken off, occupying an unassuming location in a field behind a barn at Ballochroy farmhouse on the west coast of the Kintyre peninsula, Argyll, Scotland. There is, however, a good view over the coast to the west, and this view is key to understanding its significance, for this modest monument is one of the earliest and most famous examples of a megalithic “observatory” put forward by Alexander Thom, during the 1950s. It assumed a central place in the controversies that raged for more than two decades over Thom’s theories.
Ballochroy encapsulates Thom’s idea that prehistoric Britons used features on distant horizons as astronomical foresights in order to observe and record the motions of the sun and moon to remarkable precision. The central stone at Ballochroy has a broad, flat face oriented across the alignment that points northwest, directly at the slopes of Corra Bheinn, a mountain on the Island of Jura some 31 kilometers (19 miles) away. On the summer solstice, the tip of the sun’s disc twinkled down the indicated slope; a couple days before or after, when the sun’s path was just slightly lower, it would not have been visible. The row of three stones itself points southwestward toward a small island called Cara Island about 12 kilometers (7 miles) away. Close to the winter solstice, the tip of the sun’s disc gleamed to the right of the island as it set; on the solstice itself this would not have been the case.
The best evidence supporting the theory that Ballochroy was a “solar observatory” is that there are not one but two foresights at the same site, marking the setting sun at both of the solstices. Surely such a coincidence could not have arisen by chance? And yet many critics raised doubts. One of the other standing stones in the row also has a broad, flat face pointing northwestwards, but this one points at a different mountain. And the alignment along the row is very broad, encompassing not only the right-hand end of Cara Island but also its left-hand end and central peak as well. If we are fair with the data, then we should admit the existence of at least a few other candidates for foresights that are equally plausible but have no ready astronomical explanation.
On the other hand, the fact that the claimed alignments are so precise means that we can use the slow change in the setting path of the solstitial sun century by century (due to the gradual change in the obliquity of the ecliptic) to calculate the best-fit dates for the two foresights and see if they coincide. The result is stunning: the best-fit date is pretty much the same for both foresights, around 1600 B.C.E., and this is a date that is certainly plausible archaeologically.
Yet archaeological and historical evidence has all but destroyed the idea that Ballochroy is a precise solstitial observatory. There is, and was, more to this monument than three stones in a row. A drawing by the antiquarian Edward Lhuyd in 1699 clearly shows three cairns in line with the three stones, one of them so large that it would have blocked the view to Cara Island, together with a fourth stone beyond. The burial cist (a box-shaped tomb with four side slabs) that was originally covered by this mound is still visible at the site, although the mound and the other features sketched by Lhuyd have been destroyed. The remains of this cairn were excavated in the 1960s, and the archaeological evidence indicates that it is very unlikely to have been constructed as late as the mid-second millennium
B.C.E. If the stones were erected at the date indicated by the two alignments, then one of them was always blocked by the cairn. Though a few have argued that people might have stood atop the cairn to make the observations, this is special pleading. Being realistic, we are forced to conclude that the solstitial alignment of the stone row at Ballochroy, if intentional at all, was only of a low precision: it was not an observing instrument.
The example of Ballochroy remains important to archaeoastronomers because it demonstrates the dangers of enthusiastically endorsing alignments that seem to fit an astronomical theory while ignoring other possibilities because they don’t. This isn’t being fair with the evidence. It also shows the importance of the broader context of archaeological and, where we have it, historical evidence.
See also:
Astronomical Dating; Megalithic “Observatories”; Methodology; Thom,
Alexander (1894–1985).
Short Stone Rows.
Obliquity of the Ecliptic; Solstices.
References and further reading
Burl, Aubrey.
UK: Shire, 1983. Ruggles, Clive.
Haven: Yale University Press, 1999.
The Barasana are a group of forest-dwellers in the Colombian Amazon. They survive by a mixture of fishing, hunting, and gathering, supplemented by slash-and-burn agriculture. June, July, and August (in our calendar) are difficult months for them, since their regular food sources are scarce. But at this time of year pupating caterpillars fall down from the trees and provide a much-needed source of nutrition. The date this happens coincides with the time when the Caterpillar Jaguar, a constellation regarded by the Barasana as (among other things) the Father of Caterpillars, rises higher and higher in the sky at dusk. Since the Caterpillar Jaguar is formed by stars in our constellations of Scorpius and Cetus, it is easy to explain, from a Western perspective, the association that the Barasana observe: the time of year following the acronical rising of Scorpius and Cetus happens to be the time of year when several species of caterpillar pupate.
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