The role of astronomy in the anomalous orientations of two khmer state-temples

📝 Abstract

Among the magnificent temple complexes built during the Khmer empire, two single out both for their distance from the Angkor heartland as well as for their anomalous, not cardinal, orientation: Koh Ker and Preah Khan of Kompong Svay. Their orientations are shown here to be connected with two relevant astronomical phenomena, namely the zenith passages of the sun and the rising of the Moon at the northern maximal standstill, respectively.

💡 Analysis

Among the magnificent temple complexes built during the Khmer empire, two single out both for their distance from the Angkor heartland as well as for their anomalous, not cardinal, orientation: Koh Ker and Preah Khan of Kompong Svay. Their orientations are shown here to be connected with two relevant astronomical phenomena, namely the zenith passages of the sun and the rising of the Moon at the northern maximal standstill, respectively.

📄 Content

THE ROLE OF ASTRONOMY IN THE “ANOMALOUS” ORIENTATIONS OF TWO KHMER STATE-TEMPLES Giulio Magli School of Civil Architecture, Politecnico di Milano, Italy Giulio.Magli@polimi.it Among the magnificent temple complexes built during the Khmer empire, two single out both for
their distance from the Angkor heartland as well as for their “anomalous” - not cardinal –
orientation: Koh Ker and Preah Khan of Kompong Svay. Their orientations are shown here to be
connected with two relevant astronomical phenomena, namely the zenith passages of the sun and
the rising of the Moon at the northern maximal standstill, respectively.

1. Introduction The Khmer empire flourished between the 11 and the 13 century AD. The heartland of the empire was in the vast Cambodian lowlands, where the kings adopted monumental architecture as a means for the explicit representation of their power, and constructed a series of masterpieces, among which Angkor Wat and Angkor Thom are universally known (Jacques and Lafond 2004). The first complexes to be constructed are those of Roulos, while later the kings will move to nearby Angkor area, some 15 kilometers to the north. There are, however, two exceptions. One is Koh Ker, located in northern Cambodia some 85 kilometers north-east of Angkor. The other is actually the hugest complex ever built in Cambodia. Usually called Preah Khan of Kompong Svay, to distinguish it from the Angkor temple with the same name, it is located in the Preah Vihear province some 100 Kms east (and we shall return on the meaning of this word “east” in due course) of Angkor. The function of such architectural ensembles, composed by huge barays (water reservoirs), vast rectangular enclosures enclosing a central temple, palaces, and auxiliary temples and buildings was quite a complex one, as they functioned as royal residence (capital) and main center of cult (state- temple) attesting to the beliefs and religiosity of the king. To complicate matters, the relationship between Buddhism and Hinduism – sometimes exclusive, sometimes sincretist - had a complex interplay with the dedication and the subsequent extensions of these buildings, not to say of later phases of Buddhism/Hinduism explicit conflicts and consequent defacing of temples’ images. In any case, construction of the temples was clearly considered as mandatory to attest to the greatness and in some sense to the divinity of the king. The presence of a complex religious symbolism is self- evident, and this is reflected in the planning and in the orientations of these buildings (see e.g. Malville and Gujral 2000, Kak 2001). It is, in particular, well known that almost all the temples, enclosures and barays of Angkor and Roulos are oriented cardinally, with main entrance to the east (except Angkor Vat, which opens to the west). Curiously however, this pattern is not respected at the two above mentioned complexes located out of the heartland, so that their orientations can be defined as “anomalous”. This fact has been repeatedly noticed in the specialized literature, but never explained. In this paper we show that these two orientations can be easily interpreted in terms of two very relevant astronomical phenomena: the rising of the sun in the days of the zenith passage for Koh Ker, and the maximal northern standstill of the Moon for Preah Khan. The impressive topographical relationship between Preah Khan and Angkor Vat is also analyzed in this context.

2. The orientation of Koh Ker Koh Ker was the residence of king Jayavarman IV in the mid 10th century AD. The site is characterized by a huge baray and by a 36-meters tall stepped pyramid, which is located in axis with the main temple, the Prasat Thom. The entire project exhibits a peculiar orientation at azimuth 76° (14° north of east, flat horizon) which is shared also by the short side of the baray. Sometimes topographical reasons - such as the slight south-north slope of the terrain - have been advocated for this orientation (see e.g. Uchida et al. 2014), but it is frankly difficult to believe that the architects of such a huge and complex project might have been influenced by this fact up to rotate the whole design by 14°. If we search for an astronomical interpretation, an answer is readily found. At the latitude of Koh Ker, azimuth 76° with flat horizon yields a declination of +13° 26’.1 The latitude of the site is 13° 44’ so the complex main axis is quite precisely oriented to the rising sun on the days of the zenith passages, which of course occur when the sun has a declination equal to the latitude of the place (April 27 and August 16).

3. Astronomy in the project of Preah Khan of Kompong Svay Preah Khan of Kompong Svay is composed by a series of four “concentric” rectangular enclosures which contain auxiliary temples and buildings and a central sanctuary. The exterior perimeter of about 5 km per side makes it the hugest Khmer enclosure ever built (M

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