Sundial, calendar and Khmer temples

Solar events at Prasat Phanom Rung

and other Khmer temples


Prasat Phanom Rung
Prasat Kuti Rishi Ban Khok Mueang
Prasat Sdok Kok Thom

     The author of this paper has since year 2000 promoted the spectacular sunrises and sunsets at Prasat Phanom Rung (see Bangkok Post) when the rays of the sun penetrates the ancient Khmer temple. Since then the author have conducted GPS-based field research on Khmer temples in NE-Thailand and has functioned as a free-lance advisor on archaeoastronomy and Khmer sites for the Provincial Office of Buriram.

     The Internet is a wonderful tool for sharing information. A negative side of the Internet is that incorrect information often is uncritically copied from un-scientific sources. My attribution to the Phanom Rung events in 2001 will therefore be to focus on various misunderstandings.

1. The 'miracle' of Phanom Rung
     The solar events occurs annually approximately plus/minus 14 days from the equinoxes in March and September. The dates are very easy to calculate when knowing the orientation of the structure, which is easy to measure.
     According to Concise Oxford Dictionary (10 edition, CD-version) the word miracle means ''1. An extraordinary and welcome event that is not explicable by natural or scientific laws, attributed to a divine agency. 2. An amazing product or achievement, or an outstanding example of something''. As the events are easy to calculate the slogan 'Miraculous Phanom Rung' must refer to the 2nd meaning of miracle: Amazing - or wonderful.
     I therefore agree with statements like ''when the sun’s rays pass through the 15 portals of the sanctuary at the same instant, creating a visually stunning effect'' (the Government Public Relations Department). And disagree with the continuation of the text: ''This phenomenon is rare and amazing, and it testifies to the superb skills of the temple builders'', because the phenomenon [of sunrises or sunsets aligned with the structure of a Khmer temple] is not rare: The ancient Khmer ‘master-builders’ generally orientated their temples equally towards two main directions: directly east, the cardinal direction guarded by Indra and towards the north-east, the direction guarded by Isana, an aspect of Shiva. Phanom Rung belongs to the latter group.
     Only 3% of 170 measureable Khmer temples in NE-Thailand have an orientation so that the rising sun is not aligned with the structure.

Prasat Phanom Wan Prasat Non Ku Prasat Kuti Rishi Ban Khok Mueang
     The doorways ''are so perfectly aligned that the sun's rays will shine through all ... doorways of the sanctuary in a single shaft of light''.

     The doorways of Prasat Mueang Kao (above) ''are so perfectly aligned that the sun's rays will shine through all ... doorways of the sanctuary in a single shaft of light''.


     The doorways of Prasat Kuti Rishi Ban Khok Mueang (above) ''are so perfectly aligned that the sun's rays will shine through all ... doorways of the sanctuary in a single shaft of light''. ... and sometimes the rising moon is aligned as well (above, mid).
     When there is a sunset event at Prasat Phanom Rung in March, I normally watch the sunrise the next morning framed by the doorways of the nearby Prasat Kuti Rishi Ban Khok Mueang next to Prasat Mueang Tam.
     Also Prasat Mueang Tam has two days when the rises visible straight through the door-ways - if the temple was not located in a village.

Eastern view from Prasat Khao Noi
Eastern view from Prasat Khao Lon
Equinox sunrise at Prasat Sdok Kok Thom aligned with the eastern baray.

     Prasat Khao Noi is located on a small mountain with a splendid view towards north-east; unfortunately some trees are obscuring straight east, the orientation of the temple.
     Prasat Khao Lon is also located on a small mountain and also here trees are obscuring the horizon. An inscription found at Prasat Khao Lon informs about the date when the temple was consecrated. This date does not coincide with the date when the sun rises (and rose) aligned with the structure of the temple.
     Prasat Sra Chaeng is located on a mountain chain with a splendid view towards east. The temple is so ruined that the eastern doors have collapsed. Due to its isolated location I have not visited it at equinox, when the sun rises aligned with the structure of the temple.
     Prasat Sdok Kok Thom is orientated 90 degrees true east and the sun rises aligned with the structure at equinox. The rising sun is not visible from the sanctum. The photo above was taken from the lowest steps of the staircase leading up to sanctum and the space so narrow that only one photographer can observe the event. The photo below was taken from the sanctum at sunrise at equinox.

Eastern view from Prasat Sra Chaeng.
Sunrise seen from the location of the
linga in Prasat Sdok Kok Thom.
Sunrise seen from the eastern door of Prasat Khao Lon.


2. Archaeo-astronomical event:

     ''Astrologers have also predicted that an extraordinary astro-archaeological phenomenon will occur at sunrise.'' (Tourism Authority of Thailand): My first comment is that I am not an astrologer. Second that a sunrise aligned with the door-ways of a Khmer temple does not implicate that the sunrise indicates an astro-archaeological phenomenon.
     We have no inscriptional information evidencing that the ancient Khmers deliberately orientated these or any other temples towards the rising sun for any religious or other purposes. Astro-archaeological research on solar orientations focuses primarily on temples orientated towards the point of sunrise at the equinoxes (app. 21 March and September) and the solstices (app. 21 June and December).
     The dominating orientation of Khmer temples in NE-Thailand is towards the point of sunrise at the equinoxes. These temples are therefore - like the royal temples at Angkor - orientated 90 degrees true east. The second most important orientation is towards north-east with a spread in orientation from 70 - 90 degrees (Phanom Rung = 84.5 degrees). Khmer Hindu temples orientated towards the solstices are totally lacking.
     An orientation towards the rising sun could be archao-astronomically significant if the date was chosen deliberately, as for example if the sunrise coincides with the date, when the temple was consecrated. Two temples in E-Thailand, Prasat Sdok Kok Thom and Prasat Khao Lon, have dated inscriptions; but the dates of consecration do not coincide with the days when the sun rises aligned with the door-ways of the temple.
     Prasat Phanom Rung has left us no inscriptions informing the date of consecration; but the temple is orientated so that the time span from the sunset to the sunrise event equals app. 28 days; which is close to one tropical lunar month on 27.2 days (the synodic lunar month - from full moon to full moon = 29.5 days). So if the orientation of Prasat Phanom Rung is archaeo-astronomical significant, then the event is solar-lunar, not merely solar. For details on this tentative theory, see: 'Solar-Lunar Events at Prasat Phanom Rung' in Mueang Boran. In Thai:
สุริยัน จันทรา และราหูที่ปราสาทพนมรุ้ง: ข้อสังเกตทางโบราณดาราศาสตร์ (วารสารเมืองโบราณ), where my conclusions are: 1. No past astronomical event indicates that Prasat Phanom Rung was constructed coinciding with a celestial events (e.g. eclipse). 2. 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.
National Astronomical Research Institute of Thailand (NARIT) seems similarly reluctant to draw conclusions about Prasat Phanom Rung, writing that this ''wonderful phenomenon set forth  a question: Is it a mere coincidence, or is it an indigenous astronomical wisdom of the Khmer's ancestors?''. But anyway - and without argumentation - suggests that ''the incident in the morning of April the 3rd when the first sunshine ray of the day passed through the 15 doorways of the Phanom Rung sanctuary, a wonderful astronomical aspect which should entitle this ancient historic site to become one of the world astronomical heritages.'' If so, then some of the above temple could be taken into consideration as well...

     The pictures above are from Wat Phu in Southern Laos.

     In 2010 NARIT asked the public to ''join us at Prasat Phanom Rung for the wonderful astronomical phenomena in the early morning of April 3rd. Witness with your own eyes the first ray of the sun shines through the 15 doorways of Phanom Rung. Or watch our webcast from your bedroom computer through our website http://www.narit.or.th from 5:30 am. onwards on April 3rd. (NARIT)
     NARIT will unfortunately not be present at Phanom Rung in April 2011 and therefore not set up a webcam to cover the sunrise.
     The event attracts hundreds of tourists; but only a limited amount will be able to watch the sun through the narrow gates of the temple, which in previous years have disappointed and frustrated many visitors. The organizers should set up a camera in the middle of the door-ways and show the event on large monitors. This would benefit the general public as well as scientists. The latter need data about time of sunrise and exact path of the sun taken over a 4-year period in order to
make qualified conclusions about Prasat Phanom Rung as an astronomical device. A 4-year period is needed because the sun does rise at the same spot in continuous years, but does so in a 4-years circle:


     The graphics depicts the location of the sun (50% visible) at the horizon on the 3rd of March in various years as calculated by Astronomic Clock, my favourite program.
     Note the differences in azimuth in a 4-years circle. In 2114 and 2118 the sun rises the closest to the orientation of Prasat Phanom Rung (84*30 = 84.5 degrees).
     The difference between 2114 and 2112 is equivalent to app. 1/4 of the diameter of the sun and is observable by the naked eye when using 'astronomical devices' as the door ways of Prasat Phanom Rung (below mid) or the solar gates at my test-site (below right).
     I have observed the 4-year fluctuation of the paths of the rising sun on my test-site. Due to the chaotic situation when the sun is visible through the gates of Prasat Phanom Rung I have unfortunately not been able to do the same there. Controlled video recordings is therefore a must if scientific research is wanted.


     One unique feature of Prasat Phanom Rung is that is has door-ways penetrating the temple from east to west; normally a Khmer temple only opens towards east. This 'tunnel' or 'tube' makes the temple useful as a dioptra, one of mankind's oldest astronomical tools.
     Another unique feature is that the temple is located on a small extinct volcano. And being located above the local horizon means that the sun is visible at Phanom Rung before for example at Prasat Mueang Tam on the plain below. When the sun is 50% visible at Prasat Mueang Tam - as shown on the graphics above - the sun is 100% visible at Phanom Rung.
Controlled video recordings would be very useful to demonstrate the time differences due to different local horizon - and thereby in the future be capable of calculating the exact moment of sunrise and sunset at Phanom Rung. And hopefully in the future take a photo of the rising sun at the horizon as seen through the 15 door ways of Prasat Phanom Rung.
     Controlled scientific observations over continuous years (min. 5 years) are also needed as a part of a hitherto none existing 100 % solid argumentation for why Prasat Phanom Rung eventually has astro-archaeological significance.

Sunset aligned with a tree Prasat Phanom Rung, 7 March 2000 Equinox sunrise at my test-site.


02 March 2011 © Asger Mollerup