On the alignment of Sanchi monuments
Amelia Carolina Sparavigna
Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy
Abstract: Sanchi is a Buddhist religious center and a monumental archaeological site in India. The Sanchi monuments have interesting astronomical orientations, as shown by N. Kameswara Rao in . Here, we will discuss in particular an alignment of stupas with the sunset direction on the summer solstice. Since Sanchi latitude is close to the Tropic of Cancer, we have also that, on this day, the noon altitude is about 90 degrees. Therefore, the alignment of stupas is also giving the sunset direction of the day of the zenithal sun. Such an alignment is also observed in the planning of Sigiriya complex in Sri Lanka.
Keywords: Solar Orientation, Solstices, Architectural Planning, Satellite Images, Google Earth.
Sanchi, in Raisen District of the state of Madhya Pradesh, India, is famous for its remarkable Buddhist art and architecture, made of stupas, temples, monasteries and sculptures. The religious centre at Sanchi was founded by Emperor Asoka, in the 3rd century BCE, locating it on a hill. He erected the Great Stupa that served as the first nucleus of the Buddhist religious center. Originally, the stupa was a simple hemispherical brick structure built over the relics of the Buddha. The Sanchi site might be also considered as one of the oldest astronomical monuments in India, as discussed in . The location of Sanchi itself, as stressed in , has an astronomical significance too. The latitude of Sanchi is 23°28' N, as we can see in a Google Earth map (see Figure 1). This place is then near the Tropic of Cancer; its latitude is close to the declination of the sun on the summer solstice day: then, in Sanchi, the noon sun reaches the zenithal position on the longest day of the year. In this paper, we will discuss the peculiar alignment of two stupas with the sunset direction on the summer solstice . This alignment of stupas is also giving the sunset azimuth on the day which has the zenithal sun. Such “zenithal” alignment is also observed in the planning of another Buddhist monument, the Sigiriya complex in Sri Lanka .
Figure 1 - The location of Sanchi hill has an astronomical significance . This latitude is close to the declination of the sun on the day of summer solstice: then, in Sanchi, the noon sun is at the zenith on the longest day of the year . Note the alignment of the small stupa with respect to the Great Stupa: the yellow line corresponds to the sunset direction on summer solstice.
Orientation and alignment of Sanchi stupas
Kameswara Rao, author of Ref.1, had investigated the orientation of Sanchi stupas, showing that they could had been planned to be oriented towards the moonrise and sunset on the day of Buddha purnima (purnima means "full moon"), the birthday of Siddhartha Gautama. The Figure 2 shows the Great Stupa and other stupas and monuments. Usually, according to a geometric image of the related cosmology, the Buddhist monuments are oriented as precisely as possible towards the four cardinal points [1,3]. From the Figure 2, we can see clearly what explained in , a specific orientation of the axes of monuments, different from the cardinal one. Moreover, as observed in , there is another remarkable alignment: it is that of Stupa 2 with respect to the Great Stupa. It appears to be in the direction of sunset on the summer solstice, as we can easily appreciate from Figure 3.
Figure 2 – N. Kameswara Rao had investigated the orientation of Sanchi stupas , showing that they could had been planned to be oriented towards moonrise and sunset on the day of Buddha purnima (purnima means "full moon"), the birthday of Siddhartha Gautama.
To prepare Figure 3, we used software from the web site sollumis.com. In fact, we can view solar azimuths for any location in the world, on the satellite maps of Google Earth by means of sites such as sollumis.com or SunCalc.net. We used them for analyses proposed in [2,4-8] (the use of SunCalc was proposed in [9,10]). Sollumis.com is providing, besides the solar sunrise and sunset azimuth, also the noon altitude of the sun. We can select the location and, using the form of the site, day and month on which we want direction and height of the sun. As explained at sollumis.com, the lines on the drawing show the direction and height (altitude) of the sun throughout the day. Thicker and shorter lines mean the sun is higher in the sky. Longer and thinner lines mean the sun is closer to the horizon.
Figure 3 – The image shows the direction of the sun on summer solstice as given by sollumis.com. We find the alignment of two stupas with sunset direction.
The role of sun and light in the planning of monuments is well known. In Reference 4, for instance, we discussed and analysed orientations of Gothic cathedrals of France. These buildings have the apse facing the rising sun, according to a practice adopted during the Middle Ages, to align them with the sunrise azimuth on the day of their foundation. Other alignments had been investigated in [5-8]. In particular, in , we have discussed the orientation of the Mughal gardens of Taj Mahal. These gardens can be imagined as local horizons, symbolically embracing the motion of the sun throughout the year. In Ref.2, however, we have observed another alignment, along the direction of the sunset on the day when the sun reaches the zenith, that is, it has a noon altitude of 90 degrees. This alignment is shown by the planning of Sigiriya.
Comparing to Sigiriya
Sigiriya (the Lion Rock) is a historical and archaeological site located near the town of Dambulla, Sri Lanka. The site is dominated by a massive rock nearly 200 metres high (Figure 4). On this granite rock, a huge palace was built by King Kassapa I (477–495 CE). A series of galleries and staircases, having their origin from the mouth of a gigantic lion made of bricks and plaster, provide access to the ruins on the rock. At the foot of the rock we find the lower city surrounded by walls and embellished by terraced gardens, canals and fountains. The Sigiriya site is interesting for our discussion on the Sanchi monumental complex, because it had a planning of the gardens at the foot of the rock, connected to the path of the sun too. As we can see in the Figure 5, the axis of gardens is not cardinally oriented. It is oriented with the sunset on the day when the sun at noon has an altitude of 90 degrees. Therefore, it seems that also the zenithal sun can be represented by specific alignments, in the planning of a site, according to its latitude. Of course, such an alignment can be observed only in the tropical zone. In tropical regions, we have two days of zenithal sun, but just one on the lines of Tropics, such as at Sanchi. Further researches are planned to find other zenithal alignments, that is alignments of monuments with sunrise or sunset on the day of zenithal sun.
Figure 4 - Sigiriya complex in Sri Lanka.
Figure 5 - The axis of the gardens is oriented according to the sunset azimuth on the day when the noon sun is at the zenith. At Sigiriya, the zenithal sun happens twice the year. Here we see one of this days, the first of September.
 N. Kameswara Rao (1992). History of Astronomy: Astronomy with Buddhist stupas of Sanchi, Bull. Astr. Soc. India 20:87-98.
 A.C. Sparavigna (2013). The Solar Orientation of the Lion Rock Complex in Sri Lanka, International Journal of Sciences 2(11): 60-62, DOI: 10.18483/ijSci.335
 A. Volwashen (1969). Living Architecture: Indian, Grosset & Dunlap, new York.
 A.C. Sparavigna (2014). The Solar Orientation of the Gothic Cathedrals of France, International Journal of Sciences, vol. 3 n.4, pp. 6-11. DOI: 10.18483/ijSci.484. The preprint of this paper is available from arXiv, arXiv:1209.2338, Ad Orientem: the Orientation of Gothic Cathedrals of France, published on 11 September 2012.
 A.C. Sparavigna (2015). Light and Shadows in Bernini’s Oval of Saint Peter’s Square. PHILICA.COM Article number 540.
 A.C. Sparavigna (2013). The Gardens of Taj Mahal and the Sun, International Journal of Sciences, vol. 2 n. 11, pp. 104-107. DOI: 10.18483/ijSci.346
 A.C. Sparavigna (2015). Observations on the Orientation of Some Mughal Gardens. PHILICA.COM, Article number 455.
 A.C. Sparavigna (2013). Sunrise and Sunset Azimuths in the Planning of Ancient Chinese Towns, International Journal of Sciences, vol.2 n.11, pp. 52-59. DOI: 10.18483/ijSci.334
 V. Pankovic, M. Mrdjen and M. Krmar (2015). Was Lepenski Vir an Ancient Sun or Pleiades Observatory?, arXiv:1501.01108 [physics.hist-ph]
 V. Pankovic, M. Mrdjen and M. Krmar (2015). Giza Pyramids and Taurus constellation, arXiv:1502.00972 [physics.pop-ph]