alignment An alignment of a constructed or natural feature with the celestial movement of the sun, moon, or stars, or with cardinal directions.

archeoastronomy A field of scientific research that studies the astronomy of ancient cultures.

cardinal directions The four directions—north, south, east, and west.

cenotes Circular, water-filled sinkholes. Cenotes provided water for drinking and agriculture. However, some, like the Sacred Cenote at Chichén Itzá, were likely ceremonial centers; human sacrifices may have been made there.

Chac A Mayan rain god. Long, hook-nosed masks showing Chac appear on many Chichén Itzá structures.

chacmools Reclining stone figures grasping platelike receptacles, found throughout Chichén Itzá. Chacmools may have been used to receive the hearts of people who were sacrificed.

equinox Two midpoints in the sun’s yearly cycle. In the Northern Hemisphere, the vernal (spring) equinox occurs around March 21, the autumnal (fall) equinox around September 23. These are the days in the year when the hours of daylight and nighttime are equal.

Itzá A merchant and warrior people who gave Chichén Itzá its present name.

Kukulkán The feathered serpent god; a representation of him appears on the steps of El Castillo during the spring and fall equinoxes.

Maya Native people of southern Mexico and Central America.

Olmec A culture from the Mexican Gulf Coast. The Maya used their mathematical knowledge along with celestial observations to finesse a calendar created by the Olmec.

Puuc A distinct style of architecture, named for the hilly region in the southwestern Yucatan.

Quetzalcoatl The Aztec name for Kukulkán, the feathered serpent deity found at Chichén Itzá who is one of the most important figures of Mesoamerica.

solstice The day of the year when the sun reaches its extreme northerly or southerly point. In the Northern Hemisphere, the summer solstice happens near June 21, when the sun is at its northern extreme; the winter solstice occurs near December 21, when the sun is at its southern extreme.

synodic period of Venus The synodic period is the time between successive returns of a planet to the same position in the sky, as seen from earth. The synodic period of Venus is 584 days.

Toltecs A warlike people based in northern Mexico, who began to dominate Central America around AD 950.

Yucatán state and peninsula Yucatán is a state and a peninsula in Mexico; both are home to Chichén Itzá.

zenith An imaginary point directly overhead.

zenith passage The path the sun takes from sunrise, through the zenith, to sunset. The sun makes a zenith passage twice per year, in tropical latitudes only.