Many of Ohio's ancient earthworks in the USA are aligned to astronomical events, such as the apparent rising and setting of the Sun or the Moon on key dates in their cycles. The main axis of the Octagon Earthworks at Newark, for example, lines up with the moonrise at its northernmost point on the eastern horizon. Ancient Americans were paying close attention to the sky, but why?
     According to Canadian archaeologists Brian Hayden and Suzanne Villeneuve, one of the most commonly proposed answers is that farmers need to know when to plant and harvest their crops, and the solar calendar determines the growing season. Moreover, the 18.6-year-long cycle of the Moon, encoded in Newark's monumental earthworks, wouldn't be of any help at all in determining the best times to sow and reap.
     Hayden and Villeneuve surveyed 79 complex hunter-gatherer societies from around the world and discovered that 63 of them "exhibited some solstice observation or monitoring, and/or calendars (most often lunar)." This means that people were doing more than simply noticing that there seemed to be recurrent patterns in where the sun and moon rose and set. In most cases, there was "careful and accurate monitoring of solar rising/setting positions by specialists using tree, post, or rock alignments viewed from special locations."
     The reviewers concluded that the lunar and solar calendars were used for "setting the dates of feasts together with the rituals and ceremonies that accompany them." Such decisions were fraught with social and political ramifications - the food had to be gathered and prepared and there also was a delicate web of social obligations to consider. In order to successfully hold a large feast, leaders would need a precise method for figuring out "how many years, how many months or lunations, and which specific day all debts would be called in so that the required provisions would be delivered on time at a given location."
     Feasts could be timed to coincide with visually impressive astronomical events such as moonrises in alignment with monumental earthwork walls, which might seem to confer a cosmological legitimacy on the authority of the leaders who organized the feast. Ohio's Hopewell earthworks, with their precise astronomical alignments, might be the creations of groups using their hard-earned and closely guarded knowledge of celestial movements to vie with one another for political and religious dominance.

Edited from The Columbus Dispatch (18 December 2011)