The Role of Astronomy at Angkor Wat

Astronomy enters into the meaning, format, and bas-relief decoration of the temple in three different ways. First of all, when the measurements of Angkor Wat are translated into the cubit unit used in the temple's construction, lunar and solar calendrical cycles are revealed in axial and circumference lengths. Secondly, there are several solar and lunar alignments between western points along the axis and the towers in the central galleries. Both the calendrical dimensions and the alignments were definitive elements in determining the format of the temple. In addition to actual sight lines, the solstice sun casts light onto specific segments of the bas-reliefs and corridors, planned so as to literally illuminate the selected segments with solar meaning. Finally, the composition and content of the panels of bas-reliefs further define solar and lunar periodicity. In particular, the scene of the Churning of the Sea of Milk (Milky Way) has been chosen here to demonstrate its calendrical function. In the end, we find that the king himself, in conjunction with the solar god Vishnu in the central sanctuary, is an integral part of the solar and lunar symbolism revealed in the measurements, alignments, and bas-reliefs.

The temple of Angkor Wat at the site of Angkor in northwestern Cambodia was started in 1113 CE when King Suryavarman II rose to power. Suryavarman died around 1150, at which time all work on the temple came to a halt. In this brief span of 37 years, the king endowed a monument that is now recognized as one of the world's most notable architectural achievements.

Angkor Wat did not rise up from a tabula rasa, however. The Khmer architect-priests, also fully trained as astronomers, had been building temples since the sixth century. This building activity culminated in the move to Angkor around 900, and in the final architectural perfection of Angkor Wat. Never again would Khmer architecture reach the same level of attainment and precision. Only 70 years after the death of Suryavarman, all monumental building activity at Angkor stopped and by the mid-fifteenth century, the site was abandoned due to economic reasons and the repeated invasions of Thai armies.

We know that long before the Khmers moved their capital southward to Phnom Penh, they had turned away from the gods that populated the stone and brick temples of Angkor. The people of Cambodia were converting to Hinayana Buddhism in large numbers during the thirteenth and fourteenth centuries. As devotees of this widely-practiced form of Buddhism, they rejected the ancestral and regional gods that once filled the temples and unified the nation. With this rejection, the Brahmanical (Hindu) architect-priests lost their constituency. This decline in priestly support caused a slow but inexorable loss of knowledge. Decade after decade, the priests diminished in number and the practice of building astronomical alignments and data into the temples receded in memory. It is likely that by the time the Khmers moved to Phnom Penh, the architectural coding that lay hidden in Angkor Wat for eight centuries was already forgotten At least, we have no evidence that the few Brahman priests left to perform royal rites of passage were in possession of an architectural tradition that had not been practiced for approximately 150 years. With the move to Phnom Penh, Angkor and its secrets remained dormant until brought into the consciousness of the western world in the mid-nineteenth century by French explorers.

I first became excited over Angkor Wat when I discovered that two parallel corridors in the third gallery, the gallery of large bas-relief panels, were exactly 202.14 m. in length - and this precision was typical of other measurements as well. "Why would anyone build a temple to such incredible accuracy?" Intuition and logic both argued that astronomical observation might be a possible cause for these precise measurements. Dated Khmer inscriptions begin with an elaborate description of the location of the planets, sun, and moon in both the solar zodiac signs and lunar constellations on the day the event in the inscription took place. This system also mentions whether the date in question was in the waxing or waning half of the lunar month, and on which day of the week. Astronomy is listed more than once among the subjects taught to Khmer kings. Based on the evidence of stone inscriptions then, it would have been clear even to the most casual reader that astronomy played an important role in the elite strata of Khmer society.

When I first translated the measurements of Angkor Wat from meters into the original cubit length used in the construction of the temple, my suspicions about the role of astronomy were startlingly confirmed.

• The axes of the outer enclosing wall around Angkor Wat equal 365.24 cubits repeated 12 times. In other words, the exact length of the solar year in days and in solar months is defined by the north-south and east-west axes of the temple grounds.

• The circumference of the enclosing wall is 354.36 cubits repeated 24 times. That is equivalent to the exact length of the lunar year in days, and to the 12 waxing and 12 waning halves of the lunar month each year. (Because the phenomena of the waxing and waning moon is a dominant lunar feature, the half-months were individually named since the inception of astronomy in India. This practice was passed on to Cambodia from India long before the Angkor period.)

As the analysis of the measurements of Angkor Wat unfolded over the next ten years of my research, it became more and more apparent

• that the circumferences of the temple were primarily dedicated to the moon while the axes of the galleries, enclosures, and individual chambers tended to focus on the sun. This is one of many patterns that characterize the temple's measurements. Another such pattern is the steady progression from measurements embodying the largest time cycles around the periphery of the temple to measurements focusing on smaller time cycles in the central galleries. A full exegesis of these patterns is not possible in the short space of this essay, however, it is worth noting that the measurements of Angkor Wat are highly systematized and logical. They include all time measurements known to the Cambodians in the twelfth century.

As a brilliant example of the synthesis of astronomy and architecture at Angkor Wat, the solar axes of the temple lead directly to the central sanctuary, a sanctum sanctorum devoted to the supreme solar god, Lord Vishnu. Vishnu manifests as one of the solar months, and the sun itself is thought to be his emanation. As we walk along the solar axes toward the god Vishnu, we encounter two major solar alignments.

First of all, if we stand at the beginning of the bridge into Angkor Wat on the solstice days, at the intersection of the triad of western staircases, we will see the sun rise directly over the two end gateways of the main western entrance. Although observation has not been studied from this juncture on the equinox days, the central entrance tower acts as an architectural pivot for the north-south oscillation of the sun, and by its central position between the solstice gateways, is a symbol for the two equinoxes. As we shall see, there is reason to believe that Suryavarman was crowned king of Cambodia at the time of the spring equinox.

On the morning of the vernal equinox day (roughly March 21st each year), once we have passed through the main western entrances and stand facing the interior grounds of the temple, we encounter a spectacular solar alignment . At 6:35 a.m., the sun can be seen rising dead-center over the top of the central tower of the temple - about 500 m. away - when observed from the top of the first northern staircase of the western causeway. Three days later, the sun can be seen rising over the central tower for the second and last time, from the center of the western causeway at a point just a few meters south of the first observation position. We know that the Khmers celebrated their new year for three days. The new year began on the spring equinox, but the first day of the new year in an actual count did not begin until three days after the equinox. This three-day new year period is both reflected and corroborated in these two consecutive spring equinox alignments that occur just after entering Angkor Wat.

The sun was thought to begin its yearly journey on the vernal equinox day. Therefore, as the Khmers at Angkor watched the sun rise up from the central tower, it would seem as though the god Vishnu inside the sanctuary were emanating upward and outward as the solar orb. It is highly likely that music, chanting, and ritual invocation inaugurated the new year at this annual event.

The central image of Vishnu - lost long ago - may have been sculpted in the likeness of King Suryavarman. Statements in the stone inscriptions refer to images in the likeness of real people, not just kings. The statue of Vishnu would have been sculpted with royal jewelry and clothing, and the name of this image - also lost to us - would have been combined with the name of the king according to Khmer tradition. If Suryavarman was not exactly an incarnation of Vishnu, he still partook of some aspect of Vishnu's sacred nature. The name of the sun god is Surya, and "Suryavarman" translates as "protected by the sun." With the union of the king and Vishnu in the central sanctuary of Angkor Wat, the king becomes an unspoken third component in the spring equinox alignment.

Angkor Wat - like all royal pyramid-temples - was at the conceptual center of the king's capital. The city and the nation extended outward from the union of the king and his deity in the main sanctuary of this temple. For all 37 years of the reign of King Suryavarman then, the Khmer nation was particularly joined to the sun god and to Vishnu, through the temple of Angkor Wat and the king. More than just the king alone, the entire nation was "protected by the sun." The solar measurements and solar alignments at Angkor Wat were concomitantly much more meaningful as their influence and importance extended from the hub of the nation outward.

Although the sun gains stature through its conjunction with the center of Angkor Wat, Vishnu, and the king, it is worth noting that lunar alignments are also recorded along the western axis of the temple. If we look again at the dimensions noted above, we see that the western causeway measures out two ways of defining the lunar month. These are the actual days in a synodic month (29.53), and the maximum number of days of lunar visibility (28) - numerically equivalent to the maximum number of lunar constellations crossed by the moon each month. This causeway that was used for lunar observation thereby records lunar measurements at the same time. The causeway's overlay of multiple functions is typical of the measurement patterns at Angkor Wat.

Finally, there is a bas-relief of the Churning of the Sea of Milk on the east side of the third gallery that is actually a calendar in disguise. The story behind the churning of the Milky Way begins with the gods losing battle after battle to their enemies, the asuras. Worried that they would be hopelessly decimated, the gods supplicated Lord Vishnu to help them churn up the elixir of immortality from the Milky Way. Once they drank the elixir, they could never "lose" a battle again. But the task of churning the Milky Way was of epic proportions. Ironically, once Vishnu agreed to their request, the gods had to trick the asuras into joining in the churning effort by promising them a part of the elixir.

Mount Mandara, a mountain to the east of the central, cosmic mountain, Mount Meru, was uprooted and brought to the Milky Way to act as a churning pivot. The snake Vasuki who lives in the Milky Way was wrapped around the pivot, with the gods pulling on the north side of the snake and the asuras on the south side. Vishnu took his place at the center to help with the churning, and also emanated both one asura form and one god form to further help on each side of the snake. His avatar or incarnation as Kurma, the legendary tortoise, placed itself under the base of the churning pivot so it would not sink. With everyone in place, the great churning event began.

Many auspicious objects were churned up from the Milky Ocean, including the goddess of good fortune. But when the elixir finally emerged, the gods and asuras began to battle over its possession. Lord Vishnu, in his wisdom, took the elixir away with him for safekeeping, but when the battle ended the elixir remained forever out of reach. Both the gods and the asuras were destined to be mortal. Once the battle was over and the dust had settled, Indra was crowned king of the gods and the story ends.

Astronomical or geophysical realities are woven like invisible threads throughout the preceding narrative. For example, the cosmic mountain, Mount Meru, is conceived as the axis of the earth. The Khmers knew the earth was a round sphere moving through space because they had inherited that knowledge from India, where it was first recorded in the sixth century CE. The gods reside at the north celestial pole, including the summit of Mount Meru - the location of Indra's royal palace. The summit has been flattened to accommodate the palace. At the south celestial pole, on the opposite end of Mount Meru, are the asuras. When Mount Mandara is used as a churning pivot, the gods pull the pivot to the north and the asuras pull it to the south, creating a north-south oscillation. This accounts for the north-south oscillation of the sun and moon each year, while the axis of the earth, Mount Meru, remains stable (precession notwithstanding, "stable" is a good descriptive word for the axis in comparison to the oscillation of the sun and moon). In most Khmer - and indeed, in most Asian depictions of the cosmic mountain, the sun and moon are shown in space at some distance to the right and left of the mountain's peak. This seems to be either a conscious or unconscious memory of the astronomical significance of the mountain in the churning scene. For whether it is logical or not, due to human fallibility the pivot of the churning scene tended to become identified with Mount Meru. This obfuscation is more commonly found than the actual recognition of Mount Mandara as the churning pivot.

According to evidence from Thai records and Khmer inscriptions, the churning of the Milky Way was performed at the coronation of Khmer (and occasional Thai) kings. The inauguration ceremony of a new king took place at the vernal equinox. Therefore, the coronation of King Suryavarman most likely occurred at the equinox day in March (the year remains in question) soon after he came to power. Although King Suryavarman was crowned before the central tower of Angkor Wat was anywhere near finished, future equinox risings of the sun at dead center on the top of the main tower would forever recall the exact moment when Suryavarman became king. The equinox, the sun, the temple, Vishnu, and the king were therefore joined in a moment of history that was to be recalled, year after year, at the spring equinox sunrise over Angkor Wat.

The calendrical meaning of the churning relief is equally inseparable from its association with the spring equinox coronation of King Suryavarman. In fact, the number of gods and asuras in the relief count out the days between the winter and summer solstices, and the three-day equinox celebration at the beginning of the new year is symbolized by the central pivot. The god Bali, the king of the asuras holds the heads of Vasuki on the south side of the relief. During the winter solstice, the rising sun illuminates Bali completely. This agrees with the 24-hours of sunlight at the south pole at this time of year. Meanwhile, the monkey-god Sugriva who holds the tail of Vasuki on the north end of the relief panel remains in darkness at the winter solstice, in a shadow cast by a pillar. Since the gods reside above the north pole of the earth, they would be in darkness at this time of year. On the summer solstice, the sunlight and shadow effect is reversed for Bali and Sugriva, as it should be to match the light and dark at the north and south poles, respectively. On the equinox days, the center of the scene with Vishnu and Mount Mandara is bathed in full sunlight.

A deva is flying down to steady the pivot of Mount Mandara and is most likely representative of the god Indra before he was crowned king. Only an important god could be placed in this high position, above the other gods. This figure also provides an alternate count of one extra day when needed to complete the calendar.

In Indian texts, the coronation of Indra occurs just before the coronation ceremony outlined for an earthly king, at the time of the spring equinox. This bas-relief itself, in fact, appears to symbolize the coronation of King Suryavarman and the churning event that was enacted at that time.

In summary, the solar axis of Angkor Wat takes us visually and physically in a straight line from the main entrance to the central tower. As we walk along the numerical symbol for the solar year, we would see the sun and moon oscillate from north to south and back again, on either side of the axis. Once the axis reaches the central galleries, it visually ascends upward at an ever-increasing angle until it merges with the vertical height of the central tower. On the vernal equinox day, as the sun appears to rise up from the top of the tower, it is joined to us along the axis of the temple.

Vishnu lies hidden inside the tower, looking very much like the king of Cambodia in both his physiognomy and his refined jewelry and clothing. Thus, the merging of Vishnu and the king at the symbolic center of the Khmer nation was especially celebrated at the symbolic center of the solar year, when the sun is midway between its northern and southern extremes. When this profound solar, divine, and royal union was given its architectural expression in the central tower of Angkor Wat, astronomy and architecture were joined in homage to divinity and royalty. As mentioned earlier, the tower is the axis of the temple and by extension, the axis of the Khmer nation. The king and Vishnu are joined at this same axis, likened to the axis of the earth in the cosmological design of Angkor Wat. That very equinoctial axis slices through the center of the sun's oscillating movement each year. At dawn on the vernal equinox day, the union of the king and Vishnu at the heart of the Cambodian nation was celebrated with the rising sun at the heart of the annual solar journey, and at the heart of Angkor Wat. Astronomy was thus inextricably conjoined to the most profound expression of the meaning of kingship and divinity accorded in Khmer sacred architecture. The solar and lunar alignments at Angkor Wat were alignments with the gods, alignments that tied the nation to the heavens above, and alignments that imbued the king with the power to rule by divine association. As the measurements of solar and lunar time cycles were built into the sacred space of Angkor Wat, this divine mandate to rule was anchored to consecrated chambers and corridors meant to perpetuate the king's power and to honor and placate the deities manifest in the heavens above. Rarely has a temple achieved such an overwhelming conjunction of time, space, and kingship through the perfect union of architecture and astronomy.