ASTR 1210 (O'Connell) Study Guide

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5. ANCIENT ASTRONOMY

Maya pyramid El Castillo at Chichen Itza
(Catherwood, ca. 1844)

"A single lifetime, even though entirely devoted to the sky, would not be enough for the investigation of so vast a subject...And so this knowledge will be unfolded only through long successive ages. There will come a time when our descendants will be amazed that we did not know things that are so plain to them...Many discoveries are reserved for ages still to come, when memory of us will have been effaced."

Introduction to the History of Astronomy

The quote above, by Roman philosopher Seneca the Younger, from ca. 50 AD, is characteristic of the views of the most far-sighted thinkers of ancient Greece and Rome. They knew that, for all of the important discoveries about the sky that had already been made (as described in Study Guide 6), they had barely scratched the surface of understanding the sky and its denizens.

Seneca was right about the length of time it would take to achieve a more complete understanding of the cosmos. We've presented a quick overview of our modern understanding in earlier Study Guides, but most of that was accomplished only in the last century -- almost 2000 years after Seneca speculated about future discoveries. That's a measure of the difficulty in penetrating the complexity of the universe and of overcoming the limitations of our own inadequate human intuition and our pre-conceptions about what we might find. The "things that are so plain" to us today but would have been almost incomprehensible in earlier times extend well beyond astronomy to encompass all of modern science and technology.

In the next few class meetings, we explore the historical record of progress toward understanding the sky, which began in pre-literate societies over 5000 years ago.

Introduction to Ancient Astronomy

Evidence from ancient societies that left interpretable artifacts shows that many took astronomy very seriously, to the extent of including precise astronomical alignments in their buildings and ceremonial structures.

In this lecture we discuss some of the ways early societies made and recorded observations of the Sun, Moon, planets, and stars. Then, we explore two of the most dramatic examples of ancient astronomy.

Stonehenge, the striking arrangement of massive stone monoliths in southern England from before 1500 BC, encodes astronomical knowledge, but its builders left no written records, so we have no idea how they acquired that or how they perceived the universe around them.
By contrast, the Mesoamerican cultures that flourished in Mexico and Guatemala between about 500 BC and 1500 AD not only documented extensive and painstaking observations of the sky, but they also left records of a fascinating, pre-scientific cosmology built on those. Their vibrant, if violent, view of the cosmos is beautifully captured in the so-called "Aztec Calendar Stone". The Mesoamerican Maya culture is an amazing example of great accomplishments in astronomy conjoined with ferocious societal behavior.

A. Motions of the Planets on the Sky

A conspicuous feature of the naked-eye sky in the planetarium simulations shown in Lecture 4 was the motion of the five bright planets. Although not as fast as the diurnal, solar, and lunar motions, the planetary motions are considerably more complex and placed greater demands on the abilities of ancient astronomers.

[Recall that these "motions" are measured by observers on Earth with respect to the background patterns of the stars on the sky.]

As discussed in Lecture 4, these motions are a combination of (a) the effects of observing from a moving platform and (b) intrinsic movement of the planets themselves in their orbits around the Sun. We will not try to separate these now but instead will simply review a few key facts about the motions revealed by our Starry Night simulator:

• The speed of the motions depends on the planet, decreasing from rapid to slow in the order: Mercury, Venus, Mars, Jupiter, Saturn.

• The general (average) motion of the planets against the star background is eastward in the sky.

• Mercury and Venus never move very far from the Sun (48 degrees in the case of Venus) and appear to move back and forth in front of or behind it.

• At least once per year, each of the planets halts its eastward motion and loops backward for a brief period before starting to move eastward again. This backward loop is called retrograde motion.

• The planets are confined to a relatively narrow band on the sky that is roughly centered on the ecliptic, the annual track of the Sun. The planets therefore are always to be found in the 12 Zodiacal constellations.

• The extreme north/south positions (i.e. distance from the celestial equator) of the Sun, Moon, and planets differ from one another.
  • We now know that these differences are determined by the inclinations of the orbital planes of the planets and Moon to the ecliptic plane.

  • The Sun moves along the ecliptic, so its maximal N/S positions are 23.5 degrees from the equator, as described in Guide 04.

  • The Moon's orbit is inclined 5 degrees to the ecliptic, so its maximal N/S positions are 28.5 degrees from the equator. 5 degrees may sound small, but it is 10 times the angular diameter of the Moon, so it is easy to distinguish on the sky.

  • The orbit of each planet has a different inclination with respect to the ecliptic. A planet's observed N/S extremes are affected both by its orbital inclination and its distance from the Earth.

The image below is a time-lapse exposure of a planetarium simulation of several years of planetary motions over about 40^o of the sky, showing the concentrated "active band" and the retrograde loops of several planets. North is up and east is to the left in the image. The planets cross the image moving to the left, except during their retrograde loops. The ecliptic runs along the center of the bright band. Large N/S departures from the ecliptic are apparent for several planets.

B. Astronomical Measurements Without Instruments

The most elaborate astronomical instruments prior to the advent of telescopes were made out of metal and wood. However, even societies that lacked metalworking skills could make reasonably careful astronomical observations using other kinds of technologies, some of which we explain next:

• Heliacal risings: Helios is the Greek word for the Sun. Stars are said to exhibit "heliacal risings" if they rise in the east just before the Sun. An illustration is shown here. This is a (rough) method of tracking the Sun's changing position with respect to the stars. Recall that the Sun moves about 1 degree east every day against the stars. Hence this is a date-keeping method. For example, in ancient Egypt a heliacal rising of the brightest star, Sirius, was used to forecast the Nile's annual flood. The method can only be used for stars bright enough to be visible in the twilight sky.
  
  A modern example of a horizon intercept

• Horizon intercepts: The alignment of a rising/setting object with distinct features on the distant horizon as seen from a special location is called a "horizon intercept." An illustration is shown above. Horizon intercepts allow one to track the date using the N/S position of the setting/rising Sun against the horizon (more accurate than using heliacal risings). It also allows tracking of the motions of the Moon and planets and, in particular, the extremes of their north/south motions. The horizon is a convenient reference plane for tracking celestial objects; it is harder to provide alignment devices that track objects when they are high in the sky.
  Note: accurate Earth-sky angular measurements of this kind require establishment of a reference direction. For instance, two fixed points yielding a well-defined fixed line toward the horizon is a reference against which to measure anglular positions of intercepts. The two points could both be natural (e.g. a nearby rock and a tree on the distant horizon) or they could both be artificial --- the foreground road in the Moon image above, for example. The most sophisticated of the artificial reference systems were actually embedded into ancient buildings.

• Internal building alignments. Special designs, intended to assist in making astronomical measurements or to reflect a recurring important astronomical event (e.g. an equinox or solstice), have been found built into many ancient buildings. Discovery and analysis of such features is an important aspect of a new research field: "Archaeo-Astronomy" (see ASTR 3410).
  Many ancient building alignments were intended to mark the rise or set (i.e. the horizon intercepts) of important astronomical objects. Some examples:
  • The Sun at the equinoxes (east-west alignment). For example, most ancient Greek temples have their long axes aligned east-west, so that the rising or setting Sun illuminates the interiors. The bases of the Egyptian pyramids are aligned almost exactly east-west/north-south, in the case of the Great Pyramid of Khufu within 3 minutes of arc (1/20 of a degree).
    
    The "El Castillo" pyramid, built by the Maya at Chichen Itza ca 950 AD, is not closely aligned E-W/N-S, but it features raised staircases against which a rippled shadow is cast by the edges of the pyramid at sunset near the equinoxes. See the image at the right. As the sun sets, the shadow moves and is said to resemble the slithering of the feathered serpent deity Kukulkan, to whom the temple is dedicated.

  • The Sun at a solstice (its extreme N/S positions). The rise/set points of the solstices do not lie east-west, because the Sun is 23.5 degrees from the celestial equator at these times. E.g. at Stonehenge, the line of sight from the center of the monument towards "The Avenue" and "Heelstone" points toward the rising Sun on the summer solstice. A number of structures, e.g. Newgrange in Ireland (ca. 3200 BC), are oriented toward sunrise at the winter solstice (shortest day the year).

  • The Moon at its N/S extremes (28.5 degrees from the celestial equator): e.g. at Stonehenge, the line of sight over two pairs of special stones point toward Moon rise or set at the extremes. For details on the complex motions of the Moon, see Lunar Motions and Their Consequences.

  • Bright stars. The rise/set points of stars are always the same during a given year, but they do change very slowly over time because of "precession" of the Earth's polar axis. Corrections for precession based on the date of a given ancient structure must be made before possible sight lines to stars can be explored. Examples of significant stellar alignments with megalithic structures include Nabta Playa in southern Egypt, from ca. 6000 BC.

  • Planets at their N/S extremes: e.g. the Maya El Caracol observatory building contains alignments of windows and wall structures with special setting points of Venus on the western horizon.

C. Astronomical Records

Recording of observations/interpretations is the key to scientific progress.

Although pre-literate societies were able to transmit some scientific information via oral histories and recitation, they rarely progressed far in understanding the world. They had a faulty record of their own histories, let alone nature. Even crude methods of recording data provide enormous advantages. Paradoxically, low-tech stone records survive better than more elaborate paper records.
The first writing systems were developed ca. 3200 BC in the Near East (Sumeria and Egypt) and were used mainly to record imperial and dynastic histories or commercial transactions.
The earliest extant astronomical records (Chinese) are over 4500 years old. The best astronomical records prior to the European Renaissance were developed by the Babylonians, Greeks, Chinese, and Maya. At right is a Babylonian planetary almanac written in "cuneiform" script (ca. 400 BC). The script was incised on a wet clay tablet which was then fired to make a permanent record. The surviving Maya records (both carved in stone and written in ink; see below) reveal sophisticated observational capabilities.
It is difficult for people today, for some of whom time is measured mainly in minutes elapsed between text messages, to picture the gulf in time over which human civilizations developed. Written records of any kind are sparse before about 500 BC. The earliest extensive, coherent histories were written by the ancient Greek historians Herodotus and Thucydides around 430 BC. For a little context, consider this: when Herodotus visited and described the Great Pyramid of Khufu in Egypt ca. 450 BC, he was already as distant in time from its construction as we are today from the reign of Julius Caesar.

Stonehenge by moonlight

D. Stonehenge

Stonehenge, on the Salisbury plain in south-central England, is the best known of thousands of "megalithic" ("giant stone") monuments surviving from prehistoric times (roughly 3500-500 BC) in northern Europe. (Click on the thumbnail at right for information on megalithic sites in Great Britain and Ireland.) These consist mainly of standing stones, dirt mounds and ditches, and evidence of former wooden structures, now long decayed. Four examples are shown here.

Very little is known about the peoples who built these. Unlike the Maya or the Middle Eastern cultures, they did not incise their hard stone surfaces with symbols or writing, and they left no other records of any kind. Consequently, scholarly debate has raged over the purpose of such structures. There is, however, good evidence that their builders incorporated astronomical knowledge of the Sun, Moon, and bright stars in some of them. That includes Stonehenge, which is probably the best-studied ancient structure in terms of its astronomical alignments and significance.

Construction at Stonehenge took place ca. 3100-1500 BC (over 1500 years!) in several major phases. This was a massive effort, involving, for instance, transport of specially-selected 5 ton stones up to 240 miles. The image above shows Stonehenge as it might have appeared in the period 2000-1550 BC.

To put Stonehenge in its historical context, here is a timeline showing other contemporaneous cultural developments. The construction of Stonehenge started about 500 years before the Egyptians began building pyramids, but the Stonehenge people never reached the level of sophistication of the Egyptians.

Here are some more views of the modern Stonehenge.

The current-day structure consists of a series of concentric circular ditches, banks, and post-holes with a number of large standing stones clustered in the center and a few at the periphery. Originally, the large standing stones were capped with lintels, but only a few of those remain in place today. A long straight "Avenue," marked by two parallel banks, runs north-east from the main structure and ultimately connects with an ancient settlement complex several km away.

Astronomical alignments: there are both solar and lunar alignments built into Stonehenge.

• Solsticial Alignments: A line from the monument center to the "Heelstone" points toward the location of sunrise at the summer solstice (the northernmost sunrise of the year and the longest day of the year). The reverse points to sunset at the winter solstice (southernmost sunset). The Heelstone is a large, isolated stone lying outside the circular structures on the centerline of the Avenue. [Click on the thumbnail at right for a chart of the alignments.]
  Note that such "solsticial" orientations are not simply east-west (which is much more common in ancient buildings). The heelstone is north-east of the center of Stonehenge.
  A sketch of the Sun's path as it rises over the heelstone on the summer solstice as seen from the center is shown below. The stone is placed slightly south of the actual "horizon intercept," presumably because one cannot mark that point with a large standing stone and still see the Sun there.

  

• Lunar Alignments: The so-called "Station Stones" are four stones lying just inside the circular bank (labeled "SS" in the plan drawing). Lines drawn through Station Stones 92 and 93 or 91 and 94 align with the N/S maxima of the Moon's rise or set during the 18.6-year revolution cycle in the "nodes" of its orbit.
  The nodal cycle determines where on the sky the N/S maxima will occur and also controls the pattern of lunar and solar eclipses. (See Lunar Motions and Their Consequences.)
  Diodorus, a Greek historian during the 1st century BC, refers to a "19 year" cycle traditionally associated with Stonehenge and the Moon --- almost certainly the lunar nodal cycle.
  Astronomers Gerald Hawkins, in his best-seller "Stonehenge Decoded," and Fred Hoyle suggested in the 1960's that the circle of 56 "Aubrey Holes" (dug at the inner periphery of the circular mound) could have been used as an analog computer to track the motion of the Moon, Sun, and the nodes of the lunar orbit in order to predict eclipses. 56 years, or 3 nodal cycles, is required to bring solar eclipses back to approximately the same locations on Earth's surface. Though technically correct, this idea has found little support among archaeologists.

Stonehenge is situated at a unique latitude: where the lunar and solar sight lines just described cross at right angles. It is possible that the Stonehenge people chose this site for the monument because of this fact and that this is the reason they invested so much effort (estimated at 1.5 million person-days) in building it.

Before solar and lunar orientations could be built into Stonehenge, its planners must have observed the sky for many cycles---in the case of the Moon, many times 19 years. And they needed a method to pass the information on from one generation to the next (the lifespan then was only ~30 yrs). No stone, paper, or other forms of records have been found.

The most obvious stone structures (the 5 pairs of massive trilithons arranged in a horseshoe shape, see above right) were constructed last but have no clear astronomical significance.

Stonehenge is the most elaborate structure in northern Europe remaining from the period before 1500 BC. It clearly reflects the two most important sky cycles (solar and lunar). But its central function is still obscure. It may have served as an astronomical calendar tracker, a memorial, a site for religious rituals --- or all of these.

Reconstruction of Maya city Copan as it might have looked ca. 700 AD

E. Maya Astronomy

The Maya were the most advanced ancient astronomers in the Western hemisphere. They represented the pinnacle of a 2000-year "Mesoamerican" cultural tradition, preceded by the Olmecs and Zapotecs and succeeded by the Toltecs and Aztecs.

The Maya flourished 250-900 AD in the area now belonging to Mexico, Guatemala, Honduras, and Belize. They built many elaborate cities, including large pyramidal and other public & ceremonial buildings. Recent studies of Maya territory using airborne LIDAR technology has revealed extensive "suburbs" around the major cities as well as huge networks of connecting roadways and hundreds of small settlements -- all of which had been concealed by the jungle terrain. Much of this infrastructure is from the period 1000 BC - 250 AD, before the Maya "Classic" era. The scale of early Maya building had not been appreciated before the LIDAR surveys.

Maya societies had a harsh, militaristic character, and city-states frequently waged war on one another. The civilization suddenly disintegrated beginning ca. 850 AD.

The reason for the collapse of the Maya civilization still isn't understood well. The main symptom was that the people abandoned most of their cities and spread out through the forests to live in small villages. They stayed that way for hundreds of years.
A number of problems could have contributed: drought or other environmental pressures, overpopulation, disease, invasion, or political instability. Definitive causes have not yet been identified. Probably a confluence of adverse natural and human factors was at fault.
The Maya collapse was some 600 years before the arrival of the Spanish explorers (ca. 1520 AD) and had nothing to do with military conquest by Europeans.
Something similar happened ca. 1200 BC, at the end of the Bronze Age in the Eastern Mediterranean, when a dozen different, formerly interdependent, cultures (including the Mycenaean, Minoan, and Hittite empires) precipitously declined. The subsequent 400 years in Greece became known as the "Greek Dark Ages," when literacy vanished.

Not only did the Maya empire collapse, but most of their fabulous cities were abandoned and almost completely forgotten---becoming crumbled mounds swamped by jungle vegetation and known only to local people. They were only rediscovered in the 1840's by American explorer John Stephens and popularized by the artwork of Frederick Catherwood (see his watercolor of El Castillo at the top of this page). For other examples of Catherwood's work, click here.

Part of the Maya Madrid Codex with an astronomer-like figure
"eyeing" the cosmos. Click for more images of the Codex.

Maya Observations, Sky Cycles and Calendars The Maya kept detailed written records, mainly of dynastic histories but also including astronomical texts, in the form of elaborate phonetic glyphs painted onto sheets of treated bark or carved into stone. Their writing system was developed from an earlier, cruder, version first used extensively by the Zapotec civilization (ca. 500 BC). Regrettably, most paper documents were deliberately destroyed by the Spanish after the Conquest (1520 AD), and only a few "codices" survive (example pages are shown above and to the right). Fortunately, large amounts of carved material were undisturbed and are now being slowly translated. The records show a fascination--even an obsession--with astronomical time cycles. Maya astronomers made persistent, careful observations of the Sun, Moon, Venus, and other planets. They built an elaborate and complex calendar system, in which civic and religious ceremonies were tied to celestial cycles. The two major ritualistic cycles had lengths of 260 days and 52 years. In contrast to most calendars in other cultures, the concept of a lunar month did not play a major role in this system. Astronomer "daykeepers" were needed to maintain the alignment of the sacred calendars with the real sky and to divine the meaning of changes in the sky. They consequently had high status in Maya society. Despite their remarkable architectual accomplishments, the Maya had only limited metalworking skills (primarily jewelry) and therefore lacked metal observational instruments. They presumably made most of their astronomical observations using wooden sighting devices and building or horizon alignments. See this description of the design of their elaborate "El Caracol" observatory in Chichen Itza. The Maya apparently lived in deep fear of eclipses and the planet Venus. They envisioned solar eclipses as a giant serpent consuming the Sun. A preoccupation with Venus would be natural for an observationally-skilled culture because it is, by far, the brightest starlike object in the sky and exhibits very complex motions by virtue of its proximity to Earth. Viewed from Earth, Venus has a 584 day (19 month) cycle of "configurations" with respect to Sun; the Sun and Venus have a 2922 day (8 year) cycle with respect to the bright stars. The cycle features complicated motions of Venus with respect to the Earth's horizon and other astronomical objects and large changes in the Venusian brightness. (We will show simulations in class.)

Chichen Itza Today     Astronomical Tables in the Dresden Codex

• Venus was believed to be a malevolent god, whose demands for blood sacrifice at critical times led to ritual murder by the Maya of both captives and their own citizens, including children. (The Toltecs and Aztecs, who became dominant after the Maya collapse, were even more enthusiastic participants in human sacrifice.) The Maya assiduously tracked Venus to forecast the god's intent toward themselves.

• But there is no evidence the Maya understood the origin of the celestial motions, which they attributed entirely to supernatural volition.

• From the standpoint of astronomy, there is an unpleasantly sinister aspect to this. The astronomers, or "daykeepers," were so good at making observations that it's inconceivable they hadn't realized that the celestial cycles of the Moon and Venus were strictly repeatable. And the more cycles they recorded, the more confident they could be about it. In other words, they knew that human intervention made no difference to the motions in the sky. The astronomers must have colluded with the political and religious leaders in pretending that the sacrificial rituals were effective.
  There is a hint of this in the movie Apocalypto. At the start of the ostensibly terrifying solar eclipse, two priests exchange a knowing glance. They knew it was coming all along.

Uxmal, Maya city ca. 850 AD, with the Pyramid of the Magician at the left

The Long Count and the End of the World

The Maya believed in a recurring cosmic cycle of birth and destruction during which the gods struggled to nurture a fruitful human species. Three cycles, each ending in catastrophe for the world, were thought to have preceded the then-current, fourth, cycle. The cycles as interpreted by the (later) Aztecs are described here.
Time within a cycle was tracked by the Long Count, in which each day was assigned a unique number. Counts were expressed in a modified base-20 system, the longest unit of which was the baktun. A baktun is 20x18x20x20 = 144,000 days or 394 solar years long. Here is an example of an inscription giving a date in the long count calendar.
Some Maya documents suggest that a cosmic creation cycle would end in worldwide disaster after exactly 13 baktuns, or 5125 years. By cross-correlating Long Count dates with unique astronomical events and historical dates after the Spanish conquest, archaeologists have been able to convert Long Count dates to those in the Julian (Western) calendar. The starting date of the fourth cycle (and the end of the third) was determined to be 11 August 3114 BC. But that implies that the end of the fourth cycle occurred on 21 December 2012!
You can find much speculation on the Internet before December 2012 about the meaning of the cycle turnover, including irresponsible predictions of a looming Doomsday. A handy "countdown to the apocalypse" calendar is shown at the right. The predictions were nonsense, and there was, obviously, no catastrophe at the predicted time. The doomsday hucksters have since retreated into silence to count their money.
Remember that for all their skill in tracking the planets, the Maya world view was riddled with superstition, and they showed no insight regarding the true physical nature of the universe or even the size and shape of the Earth. They had counting systems but had not developed mathematical geometry, which would have helped them understand the nature of sky cycles. Their writings were vague and contradictory concerning the cosmic cycles, and some inscriptions anticipate eras as much as 20²⁰ years from now in an inconceivably distant future. Finally, as is obvious from the historical record, there was no worldwide cataclysm in 3114 BC, at the end of the previous 13-baktun cycle. Same with 2012, and we have now started the first baktun of a new cycle.

Below are examples of a Maya observatory ("El Caracol" at Chichen Itza, left) and the remarkable Aztec "Sunstone" calendar, carved in 1479 (right). Click on thumbnails for more images and an explanation of the Sunstone.

Cultural Parallels, Cultural Clashes

Mesoamerican culture developed in isolation from the world outside the Americas, and there was no contact with Eurasian cultures before Columbus arrived in 1492 AD. Maya pyramids and glyph writing resembled their Egyptian counterparts, but they had been invented completely independently and in parallel and delayed by about 2500 years. However, the Maya easily exceeded the astronomical accomplishments of almost all the Eurasian civilizations at a comparable level of development.

It is something of a shock to realize that for all their sophistication, the Maya, as well as all the other indigeneous groups of the Americas, were literally Stone Age people. They did not make extensive use of metals: for instance, they never developed even bronze weaponry, let alone steel. They did not use the wheel for travel, commerce, or the military. They did not have seagoing vessels. They did not have guns or gunpowder. They did not have horses or draft animals like oxen because those species were not present in the Western Hemisphere.

When Hernan Cortes and his Spanish Conquistadors landed on the eastern shore of Mexico in 1519, he was facing a determined, warlike society -- but one of a kind that hadn't existed in Europe or Asia for over 4000 years. The result was rapid capitulation of the Aztec capital Tenochtitlan (now Mexico City) and the subjugation of the rest of the Mesoamerican empires over the next several decades. The same fate befell the even larger Inca Empire in western South America by 1572.

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Reading for this lecture:

Bennett textbook: 3.1 (ancient astronomy)
Study Guide 5
Lunar Motions and Their Consequences
The Aztec Calendar Stone
Optional references on Stonehenge: see Gerald Hawkins, Stonehenge Decoded (1966) or John North, Stonehenge: A New Interpretation of Prehistoric Man and the Cosmos (1996).
Optional reference on Maya astronomy: Skywatchers of Ancient Mexico by Anthony F. Aveni (Univ. of Texas Press, 1980/97).
Puzzlah Preparation Questions

Reading for next lecture:

Bennett textbook: Ch. 3.2
Study Guide 6
Optional references: Bertrand Russell, A History of Western Philosophy; Arthur Koestler, The Sleepwalkers; Timothy Ferris, Coming of Age in the Milky Way; J. L. E. Dreyer, A History of Astronomy from Thales to Kepler.
Puzzlah prep:
You have two objects, A and B, both of which are the same shape. B weighs twice as much as A. You drop both simultaneously from a height of 3 feet. What happens?
1. A (the lighter object) hits the ground first.
2. B (the heavier object) hits the ground first.
3. They hit at the same time.

You should attempt your own experiments to determine the answer...don't just take the word of the readings!

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Web links:

Slides shown in lecture (pptx)
Timeline (to 1650) of important events in the early history of science and technology
Introduction to Archaeoastronomy (UMd)
Astronomy of the Egyptian Great Pyramid
Stonehenge:
Introduction to Stonehenge.Some of the illustrations above are taken from this site.
Stonehenge Factsheet from the Royal Astronomical Society
Stonehenge (Wikipedia)
Murder at Stonehenge (segment in the "Secrets of the Dead" PBS series).
Animated 3-D Model of Stonehenge
Excavations at the Stonehenge complex (Jan 2007)
Virtual Tour of Stonehenge (English Heritage)

Maya Civilization & Astronomy:
MesoWeb (good general site)
MesoAmerica Photos & Articles (Jacobs)
Photos of Maya Cities (McKenzie)
Photos of Maya Cities and comparisons to Catherwood's discovery paintings (Frogel)
Introduction to Maya Astronomy
The Maya Calendar (Wikipedia)
The Maya Calendar (Meyer)
Brief notes on the Maya calendar (Chevalier, UVa ASTR 3410)
Astronomical Contents of the Dresden Codex (Boehm)
Breaking the Maya Code (Coe). Describes how misconceptions delayed interpretation of the Maya inscriptions for decades.
El Caracol, A Maya Observatory (O'Connell)
Evidence that a massive drought caused the Maya collapse (2018)
The Aztec Calendar Stone (O'Connell)
"The Great 2012 Doomsday Scare" (E. C. Krupp)
Debunking the "2012 Doomsday". A site injecting science and common sense into the
overheated Internet rhetoric about the "predicted" end of the world on 12/21/2012.
Maya Culture on the big screen: Mel Gibson's Apocalypto
Trailer
Wikipedia entry (summary, sources, criticism)
"History Buffs" Episode (extracts, historical assessment)

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Last modified August 2023 by rwo

Text copyright © 1998-2023 Robert W. O'Connell. All rights reserved. Megalithic and Maya images from various public sources. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 1210 at the University of Virginia.