The Sun, the Moon, and Rahu at Prasat Phanom
Solar-lunar events at Prasat
Phanom Rung in Spring 2007 AD (2550 BE)
Notes on archaeo-astronomy
Test, photos, and illustrations © Asger
Photo above: The setting sun seen through all
15 gates of Prasat Phanom Rung, 7 March 2000.
Archaeo-astronomy. Aligned sunrises/sunsets. Naksatra. Total lunar eclipse.
Sidereal lunar month. Synodic lunar month. Draconic lunar month. Lunar periods.
Four annual solar events can be observed at Prasat Phanom Rung: Two in the
spring and two in the autumn. The two events in spring consist of a sunrise and
a sunset visible through all 15 doorways of the ancient Hindu sanctuary.
The solar events are actually solar-lunar events: The period between the two
events in spring (and autumn as well) is approximately 28 days, which is close
to a sidereal lunar month (the period it takes for the moon to return to the same
point on the celestial sphere).
The orientation of Prasat Phanom Rung also depicts another kind of lunar period:
A draconic lunar month: Knowledge of draconic months is essential for predicting
solar and lunar eclipses. Around the sun rise in September 2006 there was a
lunar eclipse (partial). And around the coming sunset in March 2007 there will
be a second lunar eclipse, this time total. In the autumn 2007 a second total
lunar eclipse will occur.
The 15 doorways of the ancient Shiva temple can be used as an astronomical device
called a dioptra. We do not know whether the contemporary Khmer
astronomers/astrologers actually did so, but a trained astronomer living at the
sanctuary would certainly have noted the correlation between the orientation of
the doorways of the temple and the described aspects of astronomy.
Prasat Phanom Rung is publicised as an ancient Khmer
temple that allows the rays of the sun to penetrate the 15 doorways of the
sanctuary illuminating the linga in the central sanctuary.
Initial focus was only on the sunrise in April. The
author's observations of the sunset in March 2000 and calculations of two
similar events in the autumn were published in the Bangkok Post in March 2000,
and in Silapa Watthanatham in 2003. Since 2004 Prasat Phanom Rung has been
promoted for its four annual solar events.
Unnoticed by the public is that the solar events also
have lunar aspects and accordingly should be termed solar-lunar events: When the
sun sets straight through the doorways of Prasat Phanom Rung, wait until it is
dark and note where the moon is located on the celestial sphere (near what star
or in what zodiacal sign). Four weeks later the sun will rise and be visible
straight through the doorways of the temple – and in the hours before sunrise
the moon will be located at the same spot again.
A third aspect is eclipses of the sun and the moon. In
this case the intervals between the events ca be 14 days, 28 days, 6 months, 19
years etc. The coming total lunar eclipses in 2007 will illustrate the eclipse
aspect: The night before the sun rose visible through the doorways of Prasat
Phanom Rung in September 2006 a partial lunar eclipse was observed. Six lunar
months later, at the coming sunset in March, the moon will be totally eclipsed.
The lunar eclipse will happen in the hours before sunrise and surely be
announced in radio and TV.
||Above: Eastern facade of Prasat Phanom
Prasat Phanom Rung
Prasat Phanom Rung is an ancient Khmer temple dedicated
the Hindu god Shiva and is located on the top of an extinct volcano in Buriram
Province, NE-Thailand. The location above the surrounding plains gives a unique
view of the surrounding plains – and of the celestial sphere as well.
Archaeo-astronomy is a relatively new scientific
discipline. The term archaeo-astronomy is a combination of archaeology and
astronomy, and is an interdisciplinary research being taught at university level
only at the University of Leicester, England.
The author of this paper is autodidact. He has
conducted GPS-based (1) field research on ancient Khmer temples since 1996,
having hitherto visited some 240 temples. His research also includes
experimental astronomy. On his test-site in the Phu Phan Mountains in Mukdahan
Province in NE-Thailand he has constructed a solar calendar and as a second step
constructed cardinal orientations only using the sun.
Location, orientation, and construction
date are the essential data for archaeoastronomical calculations at a given
Location: The coordinates of the eastern
gate of Prasat Phanom Rung is 14.53198 degrees North and 102.94086 East (2).
The orientation of the 15 doorways of
Prasat Phanom Rung is 84.5 degrees from celestial north (3), as determined
by observation of the sunrise visible through the temple on 7 March 2000.
The exact date of construction is not
known. The central tower, the galleries and the 15 doorways date to the 12th
century. The oldest construction at Phanom Rung is the ruined brick towers
inside the surrounding galleries, which have the same orientation as the
later additions. The dating of the brick towers is based on the type of door
columns and assumed to date to the beginning of the 10th century. Presumed
previous constructions made of perishable materials such as wood have not
been found. The unique mountaintop location suggests that the site was
likely used for religious ceremonies before the brick towers were built. The
author has therefore conducted calculations on astronomically events – such
as eclipses – from the 7th century on.
Right: Columns and door-frames of the
10th century brick towers
The solar events
The solar events at Prasat Phanom Rung as
a rule of thumb occur 14 days before and 14 days after the equinoxes (4). At
each solar event the sun will be visible through all 15 doorways over 3
succeeding days of which the day in the middle is most straight.
Sunsets in March 2007 will occur 6th, 7th and 8th.
Sunrises in April 2007 will occur the 3rd, 4th and 5th.
The moments when the sun will be aligned with the structure of the temple is
illustrated on fig. 1 and 2.
Left: Fig. 1. Sunset 7 March
Right: Fig. 2. Sunrise 4 April
The lunar events
Astronomically there are five different types of lunar
months of which three are of interest in relation to the solar-lunar events at
Prasat Phanom Rung:
1 • Synodic month of 29.5 days (5)
is easily observable and known to everyone as the period from one full moon to
the next full moon.
2 • Sidereal month of 27.3 days
(6) is the period it takes for the moon to return to the same spot on the
The moon changes position every night as compared with
the fixed stars and after one sidereal month returns to the same position in one
of the 12 zodiacal signs (figs. 3 and 4 below). The zodiacal signs are related
to the apparent annual movement of the sun round the Earth. The ancient Khmer
sages would most likely have paid attention to the 27 lunar houses or asterisms,
the naksatras (7). The Indian concept of naksatras was used by the
ancient Khmers for calendric as well as astrological purposes. The ecliptic was
divided into 27 equal parts of 13 degrees and 20 minutes of arc.
The Moon and almost all the planets (excepting Pluto)
keep within a belt eight degrees wide on either side of the ecliptic. This belt
is known as the zodiac, or rasicakra. To indicate the day-to-day position
of the Moon in relation to the stars, this belt was divided into 27 equal
naksatra divisions from a fixed initial point in the ecliptic. Each
naksatra division (8) is named after an identifying star known as
yogataras. The yogataras of the naksatra named Citra is Spica-ά
Virginis. (Sen, p. 274).
The Vedic legend (9), Satapatha Brahmana,
states that the 27 naksatras are the 27 wives of Chandra, the Moon, and
that he spends one night with each naksatra throughout the month. After
sunset 7 March Chandra will be hosted by Citra and 27.2 days later, 4
April, Chandra will have returned to Citra. (See figs 3 and 4).
|Fig. 3: 7 March 2007 (late evening)
||Fig. 4: 4 April 2007 (before dusk)
|Above: The sidereal month
around spring equinox 2007 is illustrated by the moon in the naksatra
Draconic month of 27.2 days (10) is a third feature related to the
orientation of Prasat Phanom Rung. The draconic month is vital in
calculations of eclipses. It is defined as the period after which the moon
returns to the same node of its orbit. The nodes are the invisible points on
the celestial sphere where the moon passes the ecliptic. An eclipse can only
occur when the moon is close to one of its nodes. If the moon comes from
below the ecliptic, the node is the ascending node, and if the moon comes
from above the ecliptic, the node is the descending node (11).
The draconic month is 'embedded' in the
orientation of Prasat Phanom Rung and is illustrated by the partial full
moon in September 2006 and the coming full moon in March 2007.
App. four hours before sunrise 8 September 2006 the
partial lunar eclipse was at its maximum. At sunrise the sun rose visible
through all 15 doorways of the sanctuary. Ten minutes later the moon set and
would have been visible through all 15 door-ways if not obscured by clouds.
The 9th of September the sun rose aligned with the
structure of the sanctuary.
The partial lunar eclipse 8 September 2006 at its maximum and the
beginning of the total lunar eclipse 4 March 2007 - both observed from
Six full moons after the partial lunar eclipse there will be a total lunar
eclipse in the hours before sunrise, 4 March 2007. At 05:05 (1 hour before
sunrise) the moon will be nearly eclipsed. The eclipse is total at 06:21 and the
moon will set some five minutes later – at sunrise. The sun and the moon will be
observable directly opposite one another.
At sunset the same day the rays of the setting sun will
illuminate the linga in the central sanctuary and 20 minutes after sunset the
linga will be illuminated by the rising (nearly) full moon. Neither the sun nor
the moon will be observable through all 15 door-ways. The day when the sun sets
aligned with all 15 doorways is the 3 days later.
This '6 months full-moon eclipse interval' was well
known to ancient astronomers: ''The insight that the Babylonians had at an early
date is that observed lunar eclipses are separated either by 6 synodic
months, or by one less than multiples of 6 synodic months (reflecting an
occasional 5-month interval)'' (Goldstein, p. 2).
Based on recorded observations 2500 years ago the
Babylonians also discovered that an eclipse will be repeated after 18 years and
10.33 days. They called it Saros, meaning 'repetition'.
Eclipses close to the annual solar events at Prasat
Phanom Rung come in 'bunches' with a frequency of 8-10 years: The 2006/07
'bunch' consist of the two above described lunar eclipses
(12). The next
'bunch' will consist of a total lunar eclipse on 8 October 2014 and six full
moons later total lunar eclipse, 4 April 2015. Next again are the total lunar
eclipses 8 September 2025 and 3 March 2026, also separated by 6 full moons.
Was Prasat Phanom Rung consecrated
coinciding with a solar eclipse?
The author has often been asked if Prasat Phanom Rung
could have been consecrated coinciding with a solar eclipse on a day when the
sun rose aligned with the structure of the temple. If the question implicates a
total solar eclipse, the answer is: No! Total solar eclipses are much rarer than
total lunar eclipses. From 700 AD to 931 AD (13)
only one total eclipse was visible from
Prasat Phanom Rung: 23 March 768, and did not coincide with the day when the sun
rose illuminating the deity inside the central brick tower.
18 full moons months later, 5 September 769, the sun
rose partially eclipsed (6%) and nearly aligned with the structure.
In the 8th century AD we only have two candidates (14):
Both partial solar eclipses and both one day after the sun rose aligned with the
None of the above described solar eclipses seem to be
significant enough to connect the consecration of Prasat Phanom Rung to a past
Extending the above question to include lunar eclipses,
the conclusion is negative as well.
Even lunar eclipses are more frequently observed, none
of the eclipses in the 8th and 9th seem significant enough to connect the
consecration of Prasat Phanom Rung to one of them.
The orientation might rather be connected to all those,
who appear in a '6 months full-moon eclipse interval' as described above.
Rahu and Ketu
In Khmer mythology the nodes of the moon were
personalized as Rahu (the ascending node) and Ketu (the descending
node). Rahu was an asuras (15)
who, during the Churning of the Ocean of
Milk, tried to steal some of the elixir of immortality, the amrita, which
made the gods immortal. The Sun and the Moon noted the theft and alerted Vishnu,
who immediately decapitated Rahu with his cakra
(16). But too late; Rahu already
had amrita in his mouth and his head became immortal. Rahu has since then
revengefully tried to swallow the Sun and the Moon, which we see as eclipses.
|Above: Rahu and
11th century AD. Rahu holds the moon.
Ketu got a tail of a snake - or a dragon (17)
||Above: Rahu and
Ketu, Prasat Puai Noi, Khon Kaen. 11th century AD.
Rahu ascends from a whirlwind and holds the crescent moon.
Ketu rides the simha, a mythological lion.
Rahu and Ketu are in
iconography depicted as two of the Nine Celestial Deities, the Navagraha
(lit. the 'nine planets').
The Indian navagraha friezes starts from left
with the Sun and the Moon followed by the five 'old planets' (18) and in the end
Rahu and Ketu. The friezes are mostly associated with Shiva temples.
The Khmer navagraha differs from its Indian
origin. The series also starts with the Sun and the Moon and ends with Rahu and
Ketu, but the five graha between have been replaced with some of the
eight Guardians of the Cardinal Directions, the dikpalas. Indra is the
leader of the dikpalas and is often depicted on his elephant, Airavata,
above eastern doors of Khmer temples, the orientation of which he guards. On
Khmer depictions of the Nine Deities (19), he is always presiding in the middle.
A rather ruined frieze has been excavated at Prasat
Phanom Rung. Of the four deities only two can be identified: Rahu holding the
moon and Ketu on his simha (20).
The Doors of Prasat Phanom Rung
Nearly all Khmer Hindu sanctuaries are oriented towards
east allowing the rising sun to illuminate the deity in the central tower.
One third of the Khmer temples are oriented straight
east resulting in sunrises and sunsets aligned with the structure on the equinox
days. Spring equinox, visuvat, was Vedic solar New Year and dated Khmer stone
inscriptions count their solar-lunar calendar from the new moon before equinox.
Prasat Phanom Rung is orientated 5.5 degrees from
straight east, an orientation it shares with some 20% of the Khmer temples (21).
Unique for Prasat Phanom Rung is that is it located on a mountain top and has
doorways opening towards east as well as west allowing the rising as well as the
setting sun to illuminate the central deity, Shiva's phallic symbol, the linga.
The astronomical aspects are:
1. Solar: The illumination of the linga occurring close to 14 days
before and after the two equinox days. Annually there are 4 solar events. At
each event the sun will be visible the day before and after as well. On each
day the sun will be visible for some 8 minutes.
2. Solar-lunar: The period from the solar event before equinox to the
event after equinox is close to one synodic month. The moon will be located
at the same location (zodiacal sign, naksatra) at both events.
3. Eclipses: When a solar or lunar eclipse occurs at a solar event it
will most likely be repeated with some interval at a coming solar event. The
most common interval is 6 synodic months (app. 164 days).
Right: The vehicle of Shiva, Nandin, and the
No past astronomical event indicates that Prasat Phanom
Rung was constructed coinciding with a celestial events (e.g. eclipse).
The 15 door-ways form a 76 m. long tunnel, which can be
used for calendric observations by an observer with some knowledge in astronomy,
but we do not know if it was intended by the constructor. None of the stone
inscriptions found at Phanom Rung inform us about whether the ancient sages
living at the temple paid any attention to the various types of astronomical
aspects of the orientation of the temple.
Other contemporary Khmer inscriptions praise various
kings and their royal gurus for their exceptional knowledge in various Vedic
sciences; astronomy listed as one of them.
This, together with the abundant sculptural
manifestations of the Guardian of the Cardinal Directional and the Nine Deities,
indicate that the astronomical aspects would not have gone unnoticed by the
contemplating sages, who daily worshipped the linga on the mountain temple.
Hopefully this article will help not to let the many
celestial events in 2007 go unnoticed.
1. GPS = Global Position System
2. Averaged GPS measurements done by the author.
3. Celestial north or geographic north relates to the axis of the
Earth and differs from magnetic north.
4. Equinox (wan wisuwat in Thai, from visuvat in
Sanskrit) is the day when the sun rises straight east and sets straight west and
day and night are of equal length. Spring equinox: 20 or 21 March. Autumnal
equinox: 22 or 23 September.
5. A synodic month lasts 29.530589 days on average.
6. The sidereal month is also called the orbital period and is on
27.32166155 days (average).
7. Sometimes 28 naksatras.
8. The beginning or initial point of naksatra divisions has
changed from time to time. Surya-siddhanta astronomers changed the initial point
for counting the naksatra divisions to a point in the ecliptic opposite
the star Citra (Spica-ά Virginis). The spring equinox coincided with this
initial point at AD 285 and by circa AD 400 when the Surya-siddhanta system
became current, the equinoctial point was located not very far from this point.
9. App. 3000 years ago.
10. A draconic month is also called a nodal month and lasts
27.21222082 days (average).
11. The ascending and descending nodes are also known as the dragon's
head and the dragon's tail, and are important aspects of western and oriental
astronomy. 15 days later (19 March, 2007) there will be a partial solar eclipse,
which again will be followed by a second total lunar eclipse 6 synodic months
later, at sunrise 28 August, the latter 13 days before the sunset in September.
12. App. construction year of the brick towers at Prasat Phanom Rung.
13. The 7th September 815 the sun rose illuminating the central deity and
became 5% eclipsed 3 hours later.
14. The 7th September 834 the sun rose illuminating the central deity and
became 45% eclipsed 2½ hours later.
15. The asuras were the enemies of the gods, the devas.
16. A discus shaped weapon. Etymologically the ecliptic = zodiac =
17. The descending node, Ketu, is in western mythology called the
Dragon's Tail and Rahu the Dragon's Head.
18. The planets visible by the naked eye: Mercury, Venus, Mars, Jupiter,
19. The 'Nine Deities' might be a more proper designation, as the
planetary gods have been replaced by members of the dikpalas in various
combinations and chronology.
20. Simha: Mythological lion like creature. The lion is not
indigenous to SE-Asia.
21. The orientations are based on the author's measurements of 240
temples, most of which dates from the 10th to the 13th century AD.
APPENDIX: Major celestial events in
||Total lunar eclipse
||Starts at 04:30:00
||Sunset in 15 doors
||Aligned with the structure. Moon in Citra
||Partial solar eclipse
||Starts at 07:50:55. Max. eclipsed surface:
||Sunrise in 15 doors
||Aligned with the structure. Moon in Citra
||Total lunar eclipse
||Moon rises eclipsed at sunset
||Sunrise in 15 doors
||Aligned with the structure. Moon in Magha
||Partial solar eclipse
||Not visible in Thailand
||Sunset in 15 doors
||Aligned with the structure. Moon in Magha
History of Astronomy in India. Sen, S.N and Shukla, K.S., Indian National
Science Academy, New Delhi, 1985.
On the Babylonian Discovery of the Periods of Lunar Motion, Goldstein,
University of Pittsburg.
The author's website:
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