I: Orientations of Khmer temples:
The purpose of
this field survey of Khmer temples in Thailand was to
determine era, location, and orientation; the three key
parameters in archaeo-astrological calculations.
The tools used to determine orientation were GPS,
compass, satellite images and, best of all, direct
observation of the sun, when it rises aligned with the
structure of a given temple. At for example Prasat Sdok
Kok Thom the sun rises visible through the gates on
Of 85 sanctuaries
examined 26 were too ruined or the surroundings were too
altered for an accurate orientation determination to be
possible. Results from the remaining 59 sanctuaries are
Nearly half the temples
are orientated towards true east – the direction guarded
(above right). The second largest group is
orientated to the north-east – the direction guarded by
Isana, an aspect of Shiva. The third group is
orientated slightly to the south-east.
above results detailed in groups of 5 degrees.
All temples in this survey are orientated to within ±25º
of true east, which marks the sunrises at winter and
All these temples therefore have two days each year when
the sun rises to cast its rays through the sanctuary
gates. The four temples offering the most spectacular
sunrises are Prasat Chong Sra Chaeng, Prasat Khao Lon,
Prasat Khao Noi, and Prasat Sdok Kok Thom.
No temples are orientated towards the three other
A small group of temples – all at Mueang Sri Mahosot –
are orientated close to 65º, thereby facing the rising
sun on the summer solstice. This atypical orientation is
unseen in NE-Thailand and could be because the
orientation of the ancient settlement itself is close to
65º and the sanctuaries follow this orientation.
Two temples in Eastern Thailand – Prasat Khao Lon and
Prasat Sdok Kok Thom (below) – contain
inscriptions recording the dates when the sanctuaries
were consecrated. Neither consecration coincided with a
sunrise aligned with the structure of the temple and
visible through the doors.
The days of zenith passing of the sun are not coinciding
with the days of consecration of Prasat Khao Lon and
Prasat Sdok Kok Thom.
A final issue related to archaeo-astronomy is the moon’s
northern- and southernmost rises (lunar-stices): No
temples are orientated towards the lunar-stices.
Prasat Sdok Kok Thom on
A similar orientation
of Khmer temples conducted in NE-Thailand (Isan)
covering 229 Khmer sanctuaries gave the following
results: Of the 74% measureable structures 38% are
orientated to the east, 47% to the north-east, 12% to
the south-east, and 3% to the other cardinal directions
with the prime orientation being north-east.
The Buddhist structures of Jayavarman VII show
orientation pattern different from the Hindu temples,
perhaps indicating that astronomy did not play the same
crucial role as in Hinduism.
Bai Baek is the only
sanctuary orientated towards the west, like Angkor Wat.
It is located 3 km north of the Dangrek Mountains, 11 km
west of the Ta Muean Pass and the orientation is app. 4º
north of cardinal west.
Likewise, only one sanctuary in NE-Thailand is
orientated towards the north like Preah Vihear.
This is Mueang Khaek, which is deviating 11º from
Yama, the god of death guards the south, and apparently
no Hindu temples face true south.
Two temples, Phimai and Ta Muean Thom, are orientated
towards south, or rather SSE, respectively app. 20º and
8º from cardinal south.
Among all the Khmer temples in Isan only three are
orientated so that the sun does not penetrate their
structures: Huai Khaen, Ta Pleng, and Samrong. All three
are located along the Dharmasala Route app. 45 km
south-east of Phimai. Their deviations from east are
respectively app. 39º, 39º, and 30º north of cardinal
east. Sunrise at winter solstice deviated at this
latitude 24.5º north of cardinal east. The first two
temples mentioned above are Mahayana Buddhist
‘fire-shrines’, dharmasalas. The 3rd,
Prasat Samrong, may be a Suryavarman I ‘fire-shrine’. It
shares a similar atypical orientation as Preah Khan
Towards northernmost moon-rise.
The royal temples and the
barays of the Angkorian kings were apparently attempted
to be constructed aligned with the cardinal directions,
but the ancient master-builders did not fully succeed in
The grid of the temples
and the first major baray in the Roluos Group were
aligned perfectly against the rising sun at equinox
witnessing the skills of the architect of Jayavarman III
in mid 9th century.
The first state temple, the Bakheng, shows similar
skills; but the eastern Baray – also by Yasovarman I –
deviates app. 1.5º from true east, maybe due to later
modifications during extensions by Rajendravarman.
The main orientation of the temples in the Ko Ker
complex was for some other reason been chosen to be app.
14º north of true east.
Pre Rup and Eastern Mebon of Rayendravarman II were
probably both the work of his architect
Kavindrarimayhana and are located nearly north-south of
one another, separated only 1.3 km; but have different
orientations. The state temple Pre Rup is orientated 1º
north of true east and the Eastern Mebon nearly 4º. One
degree could be considered as an acceptable construction
error: but four degrees not. Eastern Mebon is located on
an island in the huge Eastern Baray having the best
conditions for determination of cardinal direction; but
its north-south axis point exactly towards the central
tower of Pre Rup and not true south.
The following Ta Keo is orientated towards true east,
but the last two Hindu state temples, Baphoun and Angkor
Wat, deviate 0.5º, which might be an acceptable
construction error; but excludes them from being used as
‘astronomical tools’ for observing solar and lunar
rises. Archaeo-astronomers can eventually claim embedded
symbolic alignments, but not that their function was to
observe equinoctial sunrises using the temple doors as a
The last great emperor at Angkor is Jayavarman VII
whose state temple is the Bayon in the center of the 3
by 3 km walled Angkor Thom and with his Northern Baray
right north-east hereof – all orientated 1º–2º north of
Some of the major temples
in ‘the provinces’ as Sdok Kok Thom, Si Khoraphum,
Kamphaeng Yai, and Ku Kona are all orientated precisely
II: The Indian Circle
The Sun generates all the
earthly directions and controls the seasons
A short glimpse of the Angkor
area, seen from birds-view, leaves no doubt that the prime
orientation in this period was true east, and that the
temple constructors were able to achieve cardinal alignments
with high accuracy without the use of the compass, which in
this period was not used outside China.
The significance of
orientating the entrance of the abode of the gods
towards east is stated in for example the
which also contains a chapter dealing with how to
use a sanku (gnomon, ‘shadow-giver’) to
construct east-west alignments.
The gnomon is
described in most Indian treasures on astronomy in
the Siddhantic period starting from app. 500 AD and
the method is
eleventh-century Arabic scholar and astronomer Al-Biruni
The author’s gnomon
The oldest description of the
Indian Circle Method is found in the
(400-300 BC) giving instructions for construction of Vedic
fire altars: Yano
translates the Sanskrit text as follows:
‘Driving the gnomon
into the leveled (ground), and drawing a circle with
the rope whose length is equal to the gnomon
(length), one drives two pegs at (the intersections
of) the two lines where the shadow of the tip of the
gnomon falls . This is the east (-west) line.’
Re-written as (see photo
above): Fasten a stick (gnomon) on a water leveled surface
and draw a circle with radius identical to the height of the
gnomon. In the morning and in the afternoon and mark where
the shadow of the sun crosses the circle: These two marks
are orientated east-west.
North-south is perpendicular
to the east-west line and similarly simple to construct. See
graphic on next page.
Four steps in determination of the cardinal
The method is very
simple to perform and being widely described in
Indian texts we can assume that it was widely used
in India – and in ancient Kambuja as well.
The gnomon is often described
as vertical, for which there are no practical reasons.
Some of the conclusions, based on a decade of sundial
are that the crucial parameters in the Indian Circle method
are gnomon height and the ratio between height and gnomon
tip – and that the radius of the circle does not need to be
identical to the height of the gnomon.
The method for determination
of an east-west line as described in the Sulba-sutra
does not result in an exactly true east-west alignment
because the declination of the sun is slightly different in
the morning and the afternoon: In the part of the year when
the day-path of the shadow of the sun moves towards north
from day to day, it also moves slightly towards north within
one day. This results in that the point marked in the
afternoon is slightly more northerly than the point marked
This becomes evident to a gnomist within a few years of
observations of the paths of the shadow of the sun. The
ancient Indian gnomists apparently experimented with the
sanku and probably based on observations Brahmagupta was
in the 7th century the first to note this
discrepancy. In the 11th century
Sripati formulated it in a mathematical formula in Sanskrit
metric verse, which was needed to be accredited.
This error in constructing a true east-west alignment
is never the less more of academic relevance than practical,
because the error is minimal: If the method is conducted in
the months around solstice the error is practically zero.
The error is maximal in the months around the equinoxes,
when the daily paths of the sun change the most. Example: If
a 1 m. high gnomon was used in 1066 AD at latitude N 12º the
error was 1.7 mm
(equivalent to < 1 m/km) – or in simple words:
The uncertainty when
marking a point indicated by the shadow of the
gnomon tip is much larger, due to the penumbra.
Right: Photo of shadow and
its penumbra one day after equinox. Five
day-lines made by the shadow are indicated;
the distance between is app. 6 mm.
A far more serious error can
easily occur when extending an only 2 m long line on the
gnomon floor to a grid measuring kilometers. No ancient
texts give advices on this practical problem, and neither is
it mentioned in modern descriptions
of the Indian Circle.
An alternative method for
construction of cardinal alignments could be to base the
grid on a north-south alignment derived from observations of
the circumpolar stars
as probably done by ancient Chinese astronomers.
Two other methods have been described by Pichard: One
(too) simple method is to mark the shadow of the rising sun
without considering that the rising sun casts no clear
shadow until it has risen above the horizon being located
app. 1º of from true east. The other and better proposal is
to set up two vertical sticks aligned towards the rising sun
at equinox. This method will only give accurate results if
performed on a location where the altitude of the horizon is
zero; for example at a sea-shore, or at the western end of
an 8 km long reservoir or on a small mountain.
It is not explained, how the performers of the two
methods would know, when it was equinox.
Later in the same paper the
utilization of the gnomon is described and suggested as
being the most likely tool used in ancient SE-Asia, because
it is well described in Indian manuals on architecture.
Pichard erroneously emphasizes that the gnomon must be
placed exactly vertical and also classifies the Indian
Circle method as ‘more laborious and delicate’ than the more
simple sunrise observation methods. He therefore suggests
that the Vedic Circle might only have been used when
constructing major foundations as for example the royal
temples at Angkor where ‘the alignments are true east or
only differ very weakly’ – and that ‘it appears that the
loyalty to the directives given in the Indian architectural
treaties faded out in the provinces of the empire, where the
gnomon was likely not used, because almost all temples Khmer
in current NE-Thailand differ from true east’.
Pichard apparently never
performed practical experiments with neither his two
proposed ‘sun-rise methods’ nor the Indian Circle, the
latter being so simple that my two gardeners at my sundial
experiment can perform it; contrary to marking alignments
towards the rising sun with vertical poles.
The statement, that most Khmer temples in NE-Thailand
differ from true east is correct, but cannot be used as an
argument for a significant absence of equinoctial
orientations: 47% are orientated towards north-east and 38%
towards east. Adding orientations of temples in Eastern
Thailand, the distribution is equal (42% and 41º): The
ancient architects outside Angkor were capable of laying out
If they used a gnomon
following the Vedic Circle method
the error should not exceed 0.5º - the diameter of the sun.
If the deviation from true east is more than 1º the reason
was either lack of professional skill, lack of concern, or a
deliberate choice of another direction.
We don’t know which methods
the ancient Khmer architects used when setting up a cardinal
grid for building temples and associated barays. They could
have used the Indian Circle as described in manuals on
architecture and preceding manuals on astronomy. The Indian
tradition for cardinal grids dates back to the Harappan Era
some app. 2000 BC.
Mankind has shown interest in cardinal grids framing
religious structures throughout the world from Mesoamerica
to China. The architects had developed indigenous methods,
and ancient Khmer architects could as well have had their
A modern ‘indigenous method’
The sundial experiment
referred to on previous pages was performed on a mountain
top in the Phu Phan Mountain Range in Mukdahan Province,
Thailand. The aim was by simple means as a gnomon, a plumb,
water, and strings to get an idea about how pre-historic man
could have determined the equinoxes and the solstices and
constructed true cardinal grids.
Among the results was the ease of determining the
equinox days and the solvable problems about determining the
solstice days, when the sun, ‘Surya rests with the gods for
Next was the ease of constructing exact east-west
The benefits of the
experiences goes beyond archeo-astronomy: Having house
construction as my professional background, I am now more
capable of constructing roofs preventing the sun to enter
the core-house, installing solar-panels and to orientate
In the first phase I objected
literature studies and before reading about the Vedic
Circle, I developed a simple method on how to achieve
cardinal directions with an error margin less than 0.25º
from true east by observations of the rising sun on equinox:
1) At solar noon on
equinox day raise two bamboo sticks on a line
assumed to be east-west. The ground does not need to
be leveled, but the sticks must point directly
towards the sun at solar noon.
2) If the sun on
equinox morning rises behind and follows the stick,
then the orientation is true east. If not, then move
one stick until aligned with the sun.
3) When achieved then
fasten a string at points on the sticks at same
level: This string is orientated very close to true
4) With a 100 m
distance between the two sticks the alignment can be
extended with high accuracy.
Equinox day and solar noon
(when the shadow of the sun points towards north) are
determined by the gnomon (see photos on p. 149 and 150).
1 day before equinox
On equinox day
1 day after equinox
The advantages of the
‘equinox pointer’ method is that the local horizon does not
need to be at sea-level and the time of observing the sun is
not limited to be when the sun is at the horizon.
The diameter of the sun is 0.5º. Acceptable error: less
Eastern and western pointer
Dates des Inscriptions du Pays Khmer, document augmenté par
J. C. Eade, Paris, 1885 (BEFEO 93, pgs. 395-428, Paris,
A Textbook of Hindu Astronomy. India, 1858. (From: Journal
of the American Oriental Society, Vol. 6, 1959-60. Page
(ed. and tr.): Mayamata. An Indian Treasure on
Housing Architecture and Iconography. Sitaram Bhartia
Institute of Science and Research. New Delhi : Indira Gandhi
National Centre for the Arts and Motilal Banarsidass
Publishers, Delhi, 2000, c1994.
Architecture and its models in South-East Asia /; translated
and edited by Michael Smithies. Bangkok, 2003.
J. C.: Computers
vs Tables, Billard vs Golzio: Two New Date-Lists of the
Inscriptions of Kamboja, Zeitschrift der Deutschen
vol. 158, no1, pp. 73-104, 2008.
Chronologie der Inschriften Kambojas. Verifizierung und
Umrechnung von Datumsangaben der Śaka-Ära, Weisbaden, 2006.
Kramrisch, Stella: The Hindu Temple, 2 vol., University of Calcutta, 1946.
Paul: As in
Heaven, So on Earth: The Politics of Vishnu,
Shiva, and Harihara
Images in Preangkorian Khmer Civilisation, in Journal of
Southeast Asian Studies, 34 (1), pp 21-39. UK, 2003.
The Astronomical Gnomon. A Series of Interactive Experiments
in Archaeastronomy, in African Cultural Astronomy, Curent
Ethnoastronomy research in Africa,
edited by Holbrook, J.C. and Medupe R.T. University of
Nigeria Nsukka, Enuga
State, Nigeria, 2008.
Mannika, Eleanor: Angkor Wat, Time, Space and
Kingship, Honolulu, 1996.
The Dharmasala Route from Angkor to Phimai – an ancient
Route in Revival. 2004.
Solar-lunar events at Prasat Phanom Rung in Spring 2007,
Mueang Boran Journal, vol. 39.3, Bangkok 2007:
Orientation, Era and Location of Khmer temples in Isan.
Notes on the Gnomon, Un-published, 2010.
Note sur l’orientation des monuments en Asie du Sud-Est.
Aséanie, vol. 23, Bangkok, 2009.
& Sen S. N (Ed.):
History of Astronomy in India, Indian National Science
Academy, New Delhi, 1985.
M.: Knowledge of
Astronomy in Sanskrit Texts of Architecture (Orientation
methods in the Isanasivigurudevapaddhati), in Indo-Iranian
Journal 29, pp. 17-29, 1986
Interactive des Sites Archeologiques Khmer (Khmer sites in
Arts Department Thailand:
University Cultural Map Project:
Sirindhorn Anthropology Centre (SAC): Inscriptions in
Mollerup: Prasat Sdok Kok Thom:
Mollerup: Prasat Sdok Kok Thom at Equinox - Notes on
Mollerup: Prasat Sdok Kok Thom - Dating Inscription K.235:
Mollerup: Prasat Phu Phek - Not a Solar Calendar:
(for quoting endnotes
add 163 to the numbering below)
The Guardians of the Cardinal Directions, the
dikpalas, counts Indra (E), Agni (SE), Niriti
(SW), Kubera (W), Vayu (NW), Kubera (N), and Isana
The azimuth of the rising sun at solstice changes
depending on era and latitude: At Mueang Sri Mahosot
the rising sun (50% visible) would in AD 600 be at
azimuth 65.475º (app. 24.5º from true east) and in
2010 at 65.664º; the difference being equivalent to
36 % of the diameter of the sun. These figures are
calculated using modern astronomical parameters. It
could be argued that an ancient constructor would
not measure the angle of the rising sun in situ, but
use the parameter as given in the Surya Siddhanta:
24.0º. The Surya Siddhanta is a manual on astronomy
and the parameters has successfully been used to
re-calculate the dates given in Khmer inscriptions (Eade,
Mannika (1996) proposes embedded lunar alignments in
the structure of Angkor Wat; but as Angkor Wat is
not orientated exactly true east, her conclusions
should be regarded as ‘embedded symbolic
alignments’; differing from ‘true alignments’:
Angkor Wat could and cannot be used as an
astronomical devise for exact observations of
neither lunar nor solar rises. Angkor Wat is not a
Mollerup, 2008: Orientation, Era and Location of
Khmer temples in Isan. Un-published.
The results of both researches combined are: NE:
42%, E: 41 %, SE: 15%, other directions: 2%.
Orientations towards east and north-east are equally
Angkor Wat is orientated 0.5º from true west:
270.5º. Some nearly 30 temples in Cambodia are
orientated towards west (CISARK); but the exact
orientations are unknown.
The long ceremonial path of Preah Vihear is
orientated 0.5º from cardinal north: 359.5º. Some 20
temples in Cambodia are orientated towards north (CISARK);
but the exact orientations are unknown.
Two temples in Cambodia are orientated towards south
(CISARK); but the exact orientations are unknown.
The K.970 inscription is from the 10th
century (CISARK), but the structure is older and the
age not established. Jacques, 2007, p. 179, mentions
an inscription from early 11th century.
Before the reader associate with Stonehenge,
predictions of eclipses and start drawing lines on
the map connecting these sites with Stonehenge in
England and some pyramid in Mesoamerica, it should
be taken into consideration that a pyramid temple,
Preah Damrei, close to Preah Khan K.S. has its
cruciform entrance platform orientated perpendicular
to the main orientation of Preah Khan K.S.; azimuth
Stone plate for depositing auspicious objects as
jewels and gold-leafs during one of the ceremonies
conducted during the construction faze. The location
could have been in the base of a linga or in
the top-spire of the temple. Provenance unknown;
presently deposited at Prasat Sdok Kok Thom.
Jacques (2007, p. 110) gives an excellent
presentation of the temples at Ko Ker.
Swarup, 1987, p. 2.1. Introduction, by Shukla, K.
S., quoting the
Dagens, 1970: The Mayamata is
an 11th century Sanskrit text from the
Chola period in south India translated by Bruno
Dagens. The treasure mainly deals with architecture
and iconography. The gnomon is described in
chapter 6: Orientation.
Sukla, 1985, pgs 1-3, A survey of Source materials,
by K.V. Sarma:
The Vedangas are ancillary sciences of the
Veda, and two of the six are of significance to
the history of astronomy. One is the
(ritual) consisting of practical manuals on the
performance of Vedic sacrifices and household
rituals, and contains sections called Sulba-sutras
which, among other things, mention methods of
orientation of sacrificial fire-altars for performance of fire-rituals, agnihota.
Mollerup, 2010, Notes on the Gnomon, Un-published.
Kramrisch, 1946. Yano, 1986. Malville, 2008, Pichard,
Dr. Kate Spence, an Egyptologist at Cambridge
University, has in an article in Nature, 16 November
2000, proposed that the ancient Egyptians might have
used the circumpolar stars Kochab and Mirza for
aligning the Great Pyramid at Giza in Egypt straight
true north-south in the middle of the 3rd millennium
Pichard, 2009, p. 16.
If high accuracy is the aim, then this method must
be conducted over a period of 4-5 years for
eliminating the error caused by the fact, that the
sun rises only close to true east at equinox.
Pichard, 2009, p. 24.
Ibid, p. 27. My extracted translation from French.
Other indigenous methods could have been
Sunset, Prasat Phanom Rung, Buriram.