Sundial, calendar and Khmer temples

Astro-archaeology = archaeo-astronomy = Astroarchaeology = archaeoastronomy

A Solar House / Huan Surya (เฮือนสุริยะ)

A house with calendric shadows


     The concept of the Solar-House is to construct an ordinary building, where the shadows of the sun will depict the seasons of the year, giving the construction an extra dimension also functioning as a solar calendar.

     The construction of the Solar-House is very simple:
     1. The lay-out must be oriented straight true east.
     2. The long roof must be parallel to the axis of the Earth.
     3. The short roof must be perpendicular to the short roof.

     The design of the core-house under the roof can be done individually. There are no limits for the amount and sizes of the rooms. Only the angles and the orientation of the roof are fixed.


The seasons of the sun:
     Throughout a year the sun rises at different points at the horizon.
     Around New Year (21 or 22 December) the sun rises southernmost. At noon the sun is rather low on the sky. It is the coldest time of the year and the day is called winter solstice.
     Six months later (21 June) the sun rises at its northernmost point: Summer solstice.
     The two equinox days lay mid-between the solstices: Spring equinox (20 or 21 March) and autumnal equinox (22 or 23 September). On equinox day the sun rises straight east and sets straight west, and the day and the night are of the same length.
     Equinox has been revered since ancient times. Of well-known examples can be mentioned Stonehenge, the pyramids, ancient Khmer temples and old European Christian churches. Due to different reasons the annual revolution of the life-giving sun has been embedded in constructions of man.


Picture 1: The solar construction is oriented straight east-west. The long roof points towards the Northern Star and is thereby parallel with the Earth's axis.

     The design of this solar-construction, Huan Surya, reflects the personal need of the owner: A quiet working-room. Therefore double walls and no windows or doors towards the village road. The entrance is under the southern roof. The only window is in the eastern facade. In the western facade double glass-boxes opens for the rays of the equinoctial sunrise and sunset.

W: Winter solstice
E: Equinox
S: Summer solstice
Z: Zenith
P: Towards the Northern Star
Picture 2: Eastern facade
Sketch of solar-roof showing the orientation of the sun's shadow at solar noon throughout the year.


     Solar noon is the moment, when the sun's shadow passes the meridian. Solar noon deviates from clock-time up to 15 minutes throughout a year. Because the roof is oriented straight north-south, solar noon is easy to determine: When the noon shadow is aligned with the roof it is solar noon (also called high noon).

The short and the long roof must be perpendicular to one another.
The angle of the long roof from horizontal plane is 16.66, which is identical to the latitude of the location.
The room is rectangular and oriented towards the cardinal directions.

The room.

Picture 3: Sunrise two days before vernal equinox.

Picture 4: The shadows of the rising sun two days before vernal equinox

On equinox day the sun rises at true east (azimuth = 90).
On the photos above the sun is above the horizon two days after equinox day (azimuth = 92).

  Picture 5: Around the equinoxes the glass-boxes in the western wall glows red visible at sunrise from the outside and at sunset from the inside of the room.

The landscaping north of the construction.

     The landscaping of the area north of the house will depict the annual revolution of the sun. The method is simple: Mark the position of the shadow of the sun at solar noon and decorate with desired materials.

Picture 6: 27 July 2005   Picture 7: 27 August 2005   Picture 8: 24 September 2005
      At summer solstice 21 June the sun will be aligned with the first row of stones next to the wall.
Picture 9: 9 November 2005        

Other possible calendric readings:
1. The short roof will at noon be in shadow from autumnal equinox to vernal equinox.
2. The northern wall will at noon be in shadow from autumnal equinox to vernal equinox.


APPENDIX: Suan Mali - the experimental reference site.
     Data about the correct equinox and the solstices dates and solar noon is available in the literature and on the Internet.. The author gets the data from his sundial, which is located 5 km from the village (see pictures below).

     Besides the gnomon, two solar gates will illustrate when it is equinox day. Picture 12 shows the setting sun in the western gate in Suan Mali at spring equinox 2005, March 20, as seen from the Eastern Gate 80 m away. The sun set following the bamboo stick, which at solar noon was adjusted pointing directly at the sun. The angle of the bamboo is 16.66 from vertical = the latitude of the location, a simple and ancient method of determining latitude of a location. The same angle is used in the construction of the solar house (see stippled line 'E' on picture 2 above).


Picture 10 (left): Eastern Gate.

Picture 11 (above): The gnomon.

Picture 12 (right): Western Gate.


Picture 13 (left): The gnomon 2nd November 2005 at 11.05.
     The analemmic time lines will be added next year.
     The shadow will reach the yellow area on nadir day and proceed north to the upper border of the yellow area, which marks winter solstice.

Picture 14 (right): The gnomon 2nd November 2005 at 11:06. The red line depicts the path of the sun's shadow the day before.


Picture 15 (left): The rope follows the path of the shadow of the gnomon on equinox day and continues vertically as two plumb lines.
The plumb lines are used as sight lines for a future eastern gate (see below).
The orange area marks the period plus-minus 14 days from equinox day and depicts approximately one lunar month

Picture 16 (right): The gnomon 2 November 2005 at 11:07.


Picture 17 (left): The string is parallel to the equinox line (see picture 15) and thereby oriented straight east-west.

Picture 18 (right): The new eastern gate is under construction. The vertical stick is located straight east of the gnomon.


Picture 19 (right): The rising sun at vernal equinox 2005.
Blue line is mathematical horizon (or sea-level horizon). Red line depicts the path of the rising sun.
A bamboo stick will be raised substituting the red line (analogue to the bamboo stick on picture 12).



Final comments:
     The astronomical aspects explained above can be embedded in any kind of designs of any kind of constructions from garages to hotels as long as the construction is cardinally orientated and the primary roof is parallel to the axis of the Earth. At Lamai Beach on on Koh Samui Island the angle must be approximately 9.5, in Chiang Mai approximately 18.7
     The author is a building constructor by education, speaks Thai and Lao, lives permanently in Mukdahan province, where he has been working on experimental astronomy for a decade, and can on a professional basis assist with design as well as supervising the construction.



October 2005 Asger Mollerup