Archaeoastronomy is the study of the astronomy of ancient people. As a field it is relatively young, having formally begun only in the 1960s. Archaeoastronomers seek to know what celestial observations were made by an ancient society or culture. They then try to understand how those observations were made a part of the ancient society's religious customs, political life, and agricultural or hunting-gathering practices. For this reason, archaeoastronomy is often known as cultural astronomy.
Most ancient people developed a cosmology, or an understanding of the formation and structure of the universe and their place in it. Some of these people thought the sky was inhabited by Sky People, gods, departed ancestors, or other forces. While ancient people worshiped these sky powers, they also believed the powers could be used to serve human goals. Thus a moon associated with important periods in the agricultural or hunting cycle would be honored to ensure better food supplies. A desire to have the sky powers serve the needs of humans may have motivated ancient societies to take up regular observations of the skies—in other words, astronomy.
Although any written records of ancient celestial observations have been lost to history, some of the physical signs of those activities remain. Among the most intriguing are the sites that, to a modern eye, could have been used as very early observatories.
Perhaps the most well known of these early sites is Stonehenge, which stands on Salisbury Plain in southern England. A group of massive standing stones, Stonehenge was built in three phases over a period of about 400 years, beginning around 1700 B.C. Most archaeologists believe the monument served as a ceremonial or religious structure. Some astronomers, however, believe Stonehenge could have been used to observe the winter solstice (the time when the rising of the Sun is farthest south) and the extreme rising and setting positions of the Moon.
While some ancient observing sites were simple, others were much more complex. Astronomical observations figured greatly in the culture of the Maya, native people of Central America and southern Mexico. Between 700 and 1263, the Maya built the elaborate city of Chichén Itzá on the northern Yucatan peninsula. The Caracol, a building probably designed as an observatory, and several other important ceremonial buildings at Chichén Itzá featured steeply ascending steps and ornately carved and painted relief sculptures. All were almost precisely aligned to face significant Sun and Venus positions in the sky.
Mayan life was dominated by the Sun and Venus, both of which the Maya connected to warfare. Venus, a fearful power, was also associated with sacrifice, fertility, rain, and maize (corn). Maya writings have been interpreted to indicate that raids were undertaken during important Venus positions, such as its first appearance as the morning star or the evening star. These raids have come to be called star war events. Ancient manuscripts also suggest the Maya had the ability to predict solar and lunar eclipses, accurate to within a day.