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Inka Observations of the Zenith Passage of the Sun

Inka Astronomy

illustration of Zenith and anti-zenith dates (ISB_01377)

Zenith and anti-zenith dates (ISB_01377)

In 1982, Billie Jean Isbell, published: Culture Confronts Nature in the Dialectical World of the Tropics as a contribution to the conference volume: Ethnoastronomy and Archaeo-astronomy in the American Tropics, edited by A.F. Aveni and G. Urton. In that article she argues for the importance of the zenith and antizenith passage dates of the sun in Central and South American developing a figure that shows the zenith passage dates (and antizenith) for Central and South American archaeological sites. At the moment of the zenith passage of the sun no shadow is cast for a few moments at noon. In 1981 she traveled to the Ecuadorian sites of Rumicucho situated at the Equator in Ecuador, to the modern monument of La Mitad del Mundo and finally to Ingapirca, in Cañar. During that same trip, she traveled to Cuzco where excavations were underway at the Temple of the Sun and finally to Machu Picchu where recent research suggested that the Torre Militar functioned to calculate the arrival of the June Solstice. She photographed the astronomically significant structures focusing on the June solstices and the zenith and antizenith dates at these sites.

During the Cornell summer programs in Cochabamba, Bolivia 1990, 91 and 92, she conducted visits with students to significant sites around, Lake Titicaca, The Orca del Inca, Tiwanaku, the Isla del Sol, Inkallaqta and Samaypata and photographed these sites. Bolivian archaeology was emerging at the time with astronomical studies of several of these sites demonstrating that the Inka developed diverse means of observing and calculating astronomical dates. Isbell developed the idea that the suns movement back and forth on the horizon between the June and December solstices is analogous to flowing water. With research at Inkallaqta by David Pierrera and his colleagues at San Simon University in Chochabamba, it became clear that the zenith passage of the sun was also observed at Inkallaqta.

Samaypata, she argued, may be the most southern point that zenith passage of the sun can be observed on this largest petroglyph in the world (12,000 sq. meters). Early archaeological research found evidence for tropical forest cultures at the site. The metaphor of light and shadow flowing across the petroglyph as water flows is apt. The eastern face is carved with windows and the western face with channels. The central portion of the petroglyph is carved with a double channel with diamond shaped channels at the bottom. It is perhaps the largest paqcha in the Andes A crouching puma is carved into the stone at the bottom of the channels. The puma is most often associated with the underworld.

View Zenith Passage of the Sun Group


Isbell, Billie Jean. "Culture Confronts Nature in the Dialectical World of the Tropics." In Ethno-Astronomy and Archaeo-Astronomy in the American Tropics, edited by A. F. Aveni and G. Urton. Annals of the New York Academy of Sciences, vol. 385 (1982): 353-363.