Archaeoastronomy

Archaeoastronomy is an interdisciplinary field studying how ancient civilizations sought answers to cosmological questions. Observations of sky phenomena influenced many aspects of ancient cultures, including but not limited to their science, religion, architecture, and lifestyles. Archaeoastronomy helps demonstrate how early technologies developed to better observe and understand the heavens. More often than not, the phenomena of greatest interest involved various solar system objects, especially the rising, setting, and apparent motions of the Sun, Moon, and bright planets.

Overview

Archaeoastronomy combines and archaeology into a study of ancient civilizations that focuses on the relationship between their observations of sky phenomena and their science, religion, architecture, and cultural practices. In advancing the discipline, astronomers and archaeologists work alongside ethnographers, geographers, anthropologists, mathematicians, historians, and others. However, many interpretations of archaeoastronomy are controversial and open to alternate explanations.

Archaeoastronomy dates back to the late 1600s and early 1700s when the connection between ancient human-constructed structures and astronomical events was first made. Antiquarians like John Aubrey in 1678 and Henry Chauncy in 1700 studied the astronomical alignments of churches. Initial studies dealt with Middle Eastern and European cultures. As suggested by Euan MacKie, the term archaeoastronomy was first used in 1973 by Elizabeth Chesley Baity. Locations throughout the world are investigated.

The best-known archaeoastronomy site is Stonehenge in Wiltshire, England. The current structure at the site has been dated to 2500 BCE There is evidence of an older stone structure on the same site. An earthen bank and ditch encompassing the stones has been dated to 3100 BCE The circular bank-and-ditch system measures 110 meters in diameter and has a large opening in the northeast and a smaller one to the south. Flint tools and bones of deer and oxen found in the ditch date the ring’s age.

Large stones of the sarsens structure were named for the quarry where they were mined, about 40 kilometers from Stonehenge. Stones were carefully shaped before being positioned. Thirty were erected vertically in a thirty-meter circle within the earthworks structure. Thirty lintel stones were placed on top of the sarsens. Stones are held together with tongue-and-groove joints. Each sarsen is about 4.1 meters tall and 2.1 meters wide, weighing about twenty-five tons. Lintel stones are slightly smaller. Inside this circle, five triliths were arranged in a horseshoe pattern with the open end facing northeast; each trilith is a structure composed of a lintel stone and two supporting vertical stones—that is, a structure consisting of three stones (hence the name, from “tri” for “three” and “lith” for “stone”). Triliths increased in size from 6 to 7.3 meters tall in the southwest. A single sarsen of the Great Trilith remains standing. The stone is 6.7 meters tall above ground level, with another 2.4 meters buried below ground.

In 1666, Aubrey was one of the first to study Stonehenge. His work was continued by William Stukeley, who incorrectly associated the site with the Druids. In 1740, John Wood created the most accurate map of Stonehenge. Some distance outside the sarsen circle is a pointed stone called the heel stone. When viewed from the center of the sarsen circle, the Sun rises directly over the heel stone during the summer solstice. The structure also is aligned with the winter solstice sunset and the southernmost moonrise. From outside Stonehenge, the winter sunset is framed by one particular trilith.

A second wooden structure was built two miles away from Stonehenge around the same time. The Durrington Walls circle overlooks the Avon River and resembles the stone structure. However, the timber circle (or timber henge) aligns with the winter sunrise. The avenue leading to the river aligns with the summer solstice sunset. Archaeoastronomer Mike Parker Pearson believes that the two structures were linked, and each played a key role in the culture and lives of their builders. The purpose of these two henges, however, is still unclear. The Stonehenge Riverside Project, led by Pearson, found evidence that Stonehenge was a burial site. Pearson believes the site was used to bury thirty to forty generations of royal family members. The project also conducted excavations near the Durrington Walls site, finding at least three hundred homes believed to have been used as seasonal lodgings during celebrations held there.

The most famous Irish archaeoastronomy site is Newgrange. Built between 3300 and 2900 BCE, Newgrange is older than the Giza pyramids (by five hundred years) and the Stonehenge triliths (by one thousand years). The dominant feature of this site is a 12-meter-high, 76-meter-wide mound that covers an acre of ground. The mound contains an 18-meter-long passage ending in a cross-shaped room. The site is believed to be a tomb. Cremated remains have been found inside the burial chamber. A wooden circle to the southeast and a smaller one to the south of the mound were added during the Neolithic period. The larger circle has five rings of pits, with the outer one composed of wooden posts. The next inner ring was lined with clay and was used to cremate animals buried in the inner three circles of pits. The mound was surrounded by a circle of large, freestanding stones added during the Bronze Age. Newgrange was not discovered until the late seventeenth century because of slippage covering the mound’s entrance. Michael O’Kelley and his team excavated and restored the site between 1962 and 1975.

The complexity of the mound’s construction becomes obvious on the winter solstice when sunlight enters the tomb through a roof box above the entrance and shines directly down the passageway onto the chamber floor. Solar alignments have been found in other tombs, but none is as precise as Newgrange, and none includes a roof box.

The Great Pyramids of Giza, Egypt, are also known as the Pyramids of Khufu or the Cheops Pyramids. The base of the structure is nearly a perfect square, each side measuring 230 meters. The Great Pyramid is almost fifty stories high, measuring 146.7 meters. Two slightly smaller pyramids (the Pyramids of Khafre and Menkaure) also occupy the Giza complex. The three pyramids all follow north-south and east-west lines within a fraction of a degree. Archaeoastronomers propose various explanations for that orientation. In 2000, Egyptologist Kate Spence published an article with a theory for the age and alignment of the pyramids. Spence believes that pyramid construction began between 2485 and 2475 BCE. Her theory also explains why all the pyramids are slightly offline with true north. Spence argues that the builders used two faint stars, Kochab (in the Little Dipper) and Mizar (in the Big Dipper), as guide stars. In 2467 BCE, these stars were aligned directly with the north and celestial pole stars. Egyptian astronomers could locate the two stars and use a plumb line to find the northern horizon. Pyramid construction took so long that Earth’s eventually caused Kochan and Mizar to lose their exact alignment with the north. This theory explains the orientation of the pyramids and gives a more exact estimate of their age. Other scientists argue that the three pyramids represent the three stars in Orion’s belt.

The most famous Mayan city is Chichén Itzá in Mexico. At the center of the city lies El Castillo, a temple to the god Kukulcan (Quetzalcoatl). Built between 1000 and 1200 CE, El Castillo is a step pyramid with staircases on each side leading up to a central platform at the top. Each side has ninety-one steps. Counting the top platform, there are 365 steps, one for each day in the Haab, a part of the Mayan calendar. Sculptures of serpents adorn the side of the north-facing staircase. They cast a shadow at the vernal and autumnal equinoxes, making it appear a serpent was climbing down the stairs. The western side is also aligned with the setting Sun around May 25, the day that usually marks the transition between dry and rainy seasons.

Another important Mayan site is Uxmal, located on the Yucatan peninsula. The Governor’s Palace is a long, low structure built atop a large platform. The palace is aligned with the southernmost rising of Venus, which occurs once every eight years. The temple is also aligned with the pyramid of Cehtzuc on an 118°. Standing at the palace entrance, Venus’s southernmost rising would be seen directly over the Cehtzuc pyramid 4.6 kilometers away. Venus was very important to the Maya. The Governor’s Palace is covered with hundreds of glyphs representing Venus, one of the most important Mayan deities. The Maya built observatories and kept very accurate records of Venus. They recognized that Venus alternated between appearing for several months in the eastern sky before sunrise and then for several months in the western sky after sunset. The Maya used these observations and those of other celestial objects to create one of the most accurate ancient calendars.

Medicine wheels are circular stone structures with “spokes” radiating outward from a central cairn (pile of stones). The wheels were named “medicine” from the speculation that Indigenous Americans used them in healing rituals. In 1885, when George Dawson published the first paper about medicine wheels, more than 20,000 artifacts were identified throughout North America. Only 135 survive in the United States and Canada in the twenty-first century. Some wheels are more than forty-five hundred years old, while others were built in later centuries. Medicine wheels vary in type. Some have spokes that extend out of the circle up to 120 meters. Others contain more rings of stones. Medicine wheels' origin and true purpose will never be known conclusively, but they bear an unmistakable connection to the night and daytime skies.

The southernmost surviving ring is Bighorn Medicine Wheel, high in the Bighorn Mountains of north-central Wyoming, a site tentatively dated between 1200 and 1700 CE. In the 1970s, John A. Eddy studied medicine wheels and believed they were astronomically aligned. The Bighorn wheel has twenty-eight spokes radiating from a central cairn, each spoke ending in its cairn. The number of spokes is the same as the number of days in a lunar cycle. One of the spokes extends out of the ring by 3.96 meters. Eddy discovered that the longer spoke aligned with sunrise on the summer solstice. Further support for his theory is that the Bighorn Medicine Wheel, at an elevation of 9,956 feet, is almost constantly under snow, except for two months in the summer around the solstice. Another spoke aligns with the solstice sunset. Eddy linked other cairns with alignments to the rising of the stars Sirius (in Canis Major), Aldebaran (in Taurus), and Rigel (in Orion). Since these stars hold significance for several Indigenous American Tribes, Eddy believes that the wheel was used as a calendar or timepiece.

Eddy and other scientists have found similar alignments with other medicine wheels. Opponents of Eddy’s theory argue that Indigenous Americans used medicine wheels for religious or spiritual ceremonies. Having no evidence other than the wheels themselves, archaeoastronomers may never solve all of their mysteries.

Methods of Study

Archaeoastronomers use two main methodologies. Green archaeoastronomy relies only on alignments and is used when little or nothing is known about the builders of a site. Some scientists criticize this approach because it postulates that the ancients were interested in astronomy but offers no insights into why or what role it played in their cultures. Brown archaeoastronomy, by contrast, is often compared with cultural history or the history of astronomy. Brown archaeoastronomy studies historical and ethnographic records to learn about the roles astronomy played in ancient cultures. (The names of these two methods have no import other than their reference to the colors of the covers of the first published texts proposing and explaining the nature of each technique; green came first, followed by brown.)

At some sites, both methods are used. Alexander Thom developed many of the methods used in green archaeoastronomy. He examined British sites, looking for evidence of astronomy in the builders’ society. Thom looked for alignments with the Sun (on solstices and equinoxes), the Moon, and the stars. He believed one significant alignment could result from chance, but more than one, he postulated, indicated deliberate attention to celestial objects on the part of the ancient builders. Euan MacKie, one of Thom’s strongest supporters, studied British and Mayan sites, looking for proof of a link between the two societies.

Scientists used brown archaeoastronomy to interpret the Mayan city of Chichén Itzá. They studied Mayan records to determine what astronomical bodies were important in their culture. Once archaeoastronomers learned the importance of Venus to the Maya, they evaluated the site and found that many buildings aligned with the planet's rising or setting.

Anthony Aveni uses the Incan capital Cuzco as an example of the value of brown methods. The Spanish wrote records of Incan life and legends and provided most information about the culture. These records explain that Cuzco was planned extensively before it was constructed. For example, most structures have astronomical alignments—with sunrise or sunset on the solstices.

Discoveries in the field of archaeostronomy continued to be made into the 2020s. In 2024, researchers used studies augmented with Artificial Intelligence to identify over 300 previously unknown geoglyphs in the Peruvian desert. This greatly expanded understanding of ancient astronomical practices in that region.

Context

Although controversial, archaeoastronomy—studying ancient cultures' beliefs, religions, science, architecture, and cosmology—is an increasingly crucial scientific field. The astronomical alignments of buildings, structures, and cities provide a new way of thinking about ancient societies and elucidate what was known about the solar system before modern astronomy arose in the sixteenth century. These cultures' organizational, engineering, scientific, and mathematical skills are showcased by their archaeoastronomy sites. Archaeoastronomy also expands the study of the history of science and religion further into the past than has been possible by the study of written records.

However, many questions remain unanswered. What caused societies in Russia, China, Egypt, Spain, and other parts of the world to build pyramid-shaped structures? What led these cultures to study and worship the heavens? The study of archaeoastronomy can also reveal some things about humanity. Many people pay no attention to the night sky. Most cannot explain what an eclipse or solstice is. Interest in the exploration of the solar system has declined since the 1960s, even as the technology to discover more about the solar system and the universe beyond has expanded greatly. Less than one-third of all Americans and Europeans can see the Milky Way from their backyards because of urban light pollution. Modern societies lack a connection with the heavens, something that was a main component of ancient cultures. One can only wonder how the builders of Stonehenge or the Mayan temples would view this modern attitude.

Bibliography

“Archeoastronomy in Stone.” National Park Service, 23 Jan. 2024, www.nps.gov/articles/000/archeoastronomy-in-stone.htm. Accessed 10 Feb. 2025.

"A Brief Introduction to Archaeoastronomy." University of Maryland Center for Archaeoastronomy, www.grace.umd.edu/~tlaloc/archastro/cfaar‗as.html. Accessed 10 Feb. 2025.

Chamberlain, Von Del, John B. Carlson, and M. Jane Young. Songs from the Sky: Indigenous Astronomical and Cosmological Traditions of the World. Ocarina Books, 2005.

Fountain, John, and Rolf Sinclair. Current Studies in Archaeoastronomy: Conversations Across Time and Space. Carolina Academic Press, 2005.

Kelley, David, and Eugene Milone. Exploring Ancient Skies: An Encyclopedia Survey of Archaeoastronomy. Springer, 2004.

Kreier, Freda. “8 Intriguing Archaeology Discoveries of 2024.” History, 19 Dec. 2024, www.history.com/news/archaeology-discoveries-2024. Accessed 10 Feb. 2025.

Magli, Giulio. Mysteries and Discoveries of Archaeoastronomy: From Giza to Easter Island. Springer, 2009.