Archaeoastronomy is a unique branch of science that combines two disciplines – archaeology and ancient astronomy. By studying the astronomical traditions of various cultures, scientists have made some amazing discoveries in places as far apart as Stonehenge in Great Britain, the Mayan site of Uxmal in Mesoamerica, and Greece.

For many ancient peoples, observations of the heavens led to the development of calendars. Ancient calendars were quite complex. Many cultures accepted that the solar year was 365 days long, but many calendars were used. The Maya used not only a solar calendar, but a lunar calendar of 260 days, among others. The ancient Greeks followed a lunar calendar and a civic calendar, which may indicate that the lunar calendar was a neutral choice, one that was accepted by all and which would offend none.

The calendars were not used only to track the current date. They also served as a record of past events and an accurate predictor of the future. The Mesoamerican cultures raised calendars to an art form. Over centuries, they learned to track and predict eclipses and comets – no mean feat when you consider that some comets (Halley’s Comet, to name but one) have very long orbital periods. The comet may only appear once every three generations, yet they observed it, recorded it, and learned to predict its cycle.

Archaeoastronomy studies the alignment of larger structures like pyramids, burial mounds, and even henges (Stonehenge is a prime example). Using a compass or theodolite, each angle is carefully measured. Once the initial measurements have been taken, the site is analyzed.

In Beijing, for example, the Forbidden City is built with consideration for the Five Sacred Directions (North, South, East, West, and Centre). The Emperor resides in the centre of the city, and the world quite literally revolves around him – literally and metaphorically. These early attempts to impose order on a confusing world led to the Chinese art of Feng Shui.

The heavens are constantly moving and shifting. Over thousands of years, those changes add up. Scientists use a number of methods to calculate the position of stars and moons, making it possible to compare ancient structures to the ancient skies that inspired them.

Amun-Re’s temple at Karnak in Egypt shows how archaeastronomy has improved our understanding of ancient cultures. The Great Temple included a long corridor, one that would be illuminated by the midwinter sunrise – at other times of the year, the lighting was limited. This created a valuable monument to greatness, one that had hidden messages we are only now beginning to understand.

The sun rising over Stonehenge at the 2005 Summer Solstice.
The rising sun illuminates the inner chamber of Newgrange, Ireland, only at the winter solstice.