PlanetQuest: The History of Astronomy

Angkor Wat

Photo courtesy of www.andybrouwer.co.uk

Background:
One of the most spectacular structures of astronomical significance that has ever been built is the temple of Angkor Wat in what is now Cambodia.

Angkor Wat is the most famous temple at Angkor, a former capital of the Khmer empire. It was built by King Suryavarman II in the 12th century, and is as immense as it is beautiful. Surrounded by a rectangular moat 1.5 kilometers (0.9 mile) long and 1.3 kilometers (0.8 mile) wide, the structure itself consists of two rectangular walls enclosing three nested rectangular galleries that culminate in a central spire surrounded by four smaller towers. The straight lines of its moat, walls and galleries are oriented along the north-south, east-west directions, and unlike most temples in the area its entrance faces west, being approached by way of a long bridge that spans the moat.

The origins of the temple lie in what may be the world's oldest religious text, the Rigveda, one of the four Veda Samhitas of Hindu literature. This text describes the gods of heaven and earth, including the earthly god Vishnu, "The Preserver." It is to Vishnu that Angkor Wat is consecrated, and with more than mere symbolic intent. Hindu temples were built to be earthly abodes for the gods. The central sanctuary was the most sacred place, directly inline with the vertical axis of the central spire that provided the connection between the realms of heaven and Earth. The surrounding architecture of the temple would then mirror Hindu cosmology, being essentially a mandala in stone—a diagram of the cosmos itself. Furthermore, the Khmer civilization had by the time of Angkor Wat's construction incorporated the idea that a king would, after his death, be transmuted into one of the gods. Hence, it was at Angkor Wat that Suryavarman II, after his death, was believed to reside as Vishnu.

Photo courtesy of www.andybrouwer.co.uk

Astronomical significance:
Astronomy and Hindu cosmology are inseparably entwined at Angkor Wat. Nowhere is this more evident than in the interior colonnade, which is dedicated to a vast and glorious carved mural, a bas-relief illustrating the gods as well as scenes from the Hindu epic the Mahabharata. Along the east wall is a 45-meter (150-foot) scene illustrating the "churning of the sea of milk," a creation myth in which the gods attempt to churn the elixir of immortality out of the milk of time. The north wall depicts the "day of the gods," along the west wall is a great battle scene from the Mahabharata, and the south wall portrays the kingdom of Yama, the god of death. It has been suggested that the choice and arrangement of these scenes was intended to tie in with the seasons—the creation scene of the east wall is symbolic of the renewal of spring, the "day of the gods" is summer, the great battle on the west wall may represent the decline of autumn, and the portrayal of Yama might signify the dormancy, the lifeless time of winter.

Photo courtesy of www.andybrouwer.co.uk

The architecture of Angkor Wat also has numerous astronomical aspects beyond the basic mandala plan that is common to other Hindu temples. As many as eighteen astronomical alignments have been identified within its walls. To mention but three of them: when standing just inside the western entrance, the Sun rises over the central tower on the spring (vernal) equinox; it rises over a distant temple at Prasat Kuk Bangro, 5.5 kilometers (3.4 miles) away, on the winter solstice; and on the summer solstice it rises over a prominent hill 17.5 kilometers (10.9 miles) away.

Finally, some researchers have claimed that the very dimensions of many of the structures at Angkor Wat have astronomical associations. These associations emerge from consideration of the unit of length that was in use at that time, a unit known as the hat or "Cambodian cubit." There is some question as to how long a hat was, and indeed its definition may not have been uniformly applied; but a value of 43.45 centimeters (17.1 inches) for the length of a hat is suggested by the structures themselves.

Using this value, archaeologists discovered numerous dimensions of the temple that seem to have astronomical and cosmological significance—for example, the following:

• The dimensions of the highest rectangular level of the temple are 189 hat in the east-west direction and 176 hat in the north-south direction. Added together these give 365, the number of days in one year.

• In the central sanctuary, the distances between sets of steps is approximately 12 hat. There are roughly 12 lunar cycles, or synodic months (from full Moon to full Moon, say—the basis for our modern month) in one year.

• The length and width of the central tower add up to approximately 91 hat. On average, there are 91 days between any solstice and the next equinox, or any equinox and the next solstice.

Because of its orbit around the Earth, the Moon's apparent position in the sky relative to the background stars will appear to shift from night to night. Since it takes the Moon just over 27 days to complete one orbit (known as its sidereal period), it will during this time appear to move through 27 successive regions of the sky. In Hindu cosmology, these regions were known as the naksatras, or lunar mansions. In some contexts there were 27 lunar mansions, while in other contexts an additional naksatra containing the star Vega was included, giving 28 lunar mansions.

Photo courtesy of www.andybrouwer.co.uk

• The central tower at Angkor Wat contains nine inner chambers. If you total the dimensions of all of these chambers it equals 27 hat in the north-south direction and 28 hat in the east-west direction, corresponding to the possible number of lunar mansions. Also, the libraries have lengths measured along their interiors of 16 hat in the east-west direction, and either 12 or 11 hat in the north-south direction, depending upon whether or not the doorways are included. Added together, these also give either 28 or 27 hat. Finally, the north-south width of the libraries measured from the exteriors of the walls is again 28 hat.

Hindu cosmology recognizes four time periods, or Yugas, that are represented in the dimensions of the temple:

• The length of the Kali-Yuga, our current time period, is 2 x 60³ years, or 432 thousand years. The width of the moat that surrounds the temple, measured at the water level, is approximately 432 hat.
  
• The length of the Dv apara-Yuga is 4 x 60³ years, or 864 thousand years. The distance from the entrance to the inner wall is 867 hat.

• The length of the Treta-Yuga is 6 x 60³ years, or 1,296 thousand years. The distance from the entrance to the central tower is 1,296 hat.

• The length of the Krita-Yuga is 8 x 60³ years, or 1,728 thousand years. The distance from the moat bridge to the center of the temple is 1,734 hat.

Rarely in history has any culture given rise to a structure that so elaborately and expansively incorporates its concept of the cosmos. Angkor Wat stands as a striking and majestic monument in honor of the Universe and our place in it.

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References:
Kelley, D., and E. Milone, Exploring Ancient Skies: An Encyclopedic Survey of Archaeoastronomy, Springer, New York, 2005.

Krupp, E.C., Skywatchers, Shamans & Kings: Astronomy and the Archaeology of Power, John Wiley & Sons, Inc., New York, 1997.

Space and Cosmology in the Hindu Temple, by Subhash Kak

Other useful links and references:
A photographic tour with maps

NASA Ancient Observatories

Photographs and architectural plans

Photographs of Angkor Wat
More photographs of Angkor Wat

sacredsites.com
Tourism of Cambodia (includes a detailed description of the bas-reliefs)