Abstract
The Tropic of Cancer is a parallel located at the latitude of 23°26'16''. This imaginary line extends across northern Mexico from the southernmost point of the Baja California Peninsula, to the Gulf of Mexico, passing through the states of Baja California Sur, Sinaloa, Durango, Zacatecas, San Luis Potosí, Nuevo León and Tamaulipas. The Tropic of Cancer marks the northernmost position of the sun at its midday zenith, which takes place in the Summer solstice. On this day, the sun's rays hit the earth's surface vertically along the entire length of this latitude, which was supposed to be significant for the priest/astronomers of ancient times, who dedicated themselves to observing the apparent movements of the sun. It so happens that Alta Vista in Zacatecas, corresponds to the westernmost peak where this phenomenon can occur, although the date of the zenith's course differs depending on the latitude of each position and so various archaeoastronomical specialists stress how the ancient indigenous cultures, at least those dating from Mexico's Classical period, valued this finding in developing their calendars. On the other hand, the research contributes new elements for discussion because it presents a calendar of the horizon, based on of the highest peaks of the Sierra Prieta mountain range ranging from the archaeological sites of El Chapín, Cerro Pedregoso, to the excavations at El Picacho Pelón (peak El Pelón).
