ASTR 1210 (O'Connell) Study Guide


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.

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.

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 image below is a time-lapse exposure of a planetarium simulation of several years of planetary motions over about 40o 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:

C. Astronomical Records

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

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.

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.

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.

Copan Reconstruction
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.

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.

Madrid Codex
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

Dresden Codex

Astronomical Tables in
the Dresden Codex

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

The Long Count and the End of the World

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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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.