From the ruins of the structures found at Dholavira and discovery of thousands of articles of daily use, pots, jewelery, weapons and the water management system, details of which we saw earlier, it would become quite clear to anyone that the Indus-Sarswati civilization was an intellectually advanced society with advanced levels of knowledge of natural phenomenon around them. Dholavira, which was part of this civilization, was a port city, from where, regular sailings of ships to inland cities in Sarswati and Indus basins as well as to Ports in Mesopotamia took place. This is not possible without possessing calendrical information such as time of the day, time of the night, seasons, years and possibly even longer periods, and understanding the movement of the heavenly objects such as stars, Sun and Moon for navigational purposes. They also needed to have precise information about the sea tides.
During my visit to Dholavira, I had posed this question to our guide, who was kind enough to give some information about the way, basic calendrical information was maintained by the Dholavira people. According to him, certain stair cases in the Citadel ruins, were found to have 7, 15 and 30 steps. It was easily possible, by using markers, which probably were shifted every day, to know what day of the week or fortnight or month that day was. By using similar methods, it was possible to know the month. This information was quite useful, but to have precise information about sea tides and seasons, they still had to have some means by which they must have related their basic calender of steps with seasonal marks like summer and winter solstice days. How they did it, probably would have remained a mystery for ever, but for a chance discovery of two circular structures, by two scientists: Mr. M N Vahia from the Tata Institute of Fundamental Research (TIFR), Mumbai and Mr. Srikumar Menon from Manipal School of Architecture and Planning (Karnataka).
A group of of scientists now say that this discovery is the first identification of a structure used for observational astronomy during the Harappan Civilisation or in other words, these two circular structures was a functional astronomical observatory, with help of which, Dholavira people were able identify days of solar calender such as summer and winter solstice and use that information to conduct business, farming and other activities.
(Image may be copyrighted)
We have seen earlier that in the southeastern corner of the Dholavira city, an administrative centre of the city (named as citadel), existed within massive ramparts or walls. This citadel had two sections: castle, where residence and administrative quarters of the chief or king were located and a Bailey, where all support activities took place. M/S Vahia and Menon found ruins of a strange looking structure in this Bailey. They describe this structure in these words and I quote.
“ In the Bailey region of the city is a structure with a plan-form that is markedly different from the rest of the structures in the city and from Harappan plan-forms in general. It consists of the plinth and the foundations of what was probably a 13-room rectangular structure, of which two are circular rooms embedded within. It is located west of the Citadel and is near the edge of the terrace forming the Bailey with a drop in the west. The flat featureless horizons to the north, west and south are visible without any obstruction, while to the east the mound of the citadel obscures the horizon to a large extent. The ground slopes down to the south, where one of the artificial water reservoirs is located which would have permitted a clear view of the southern horizon.”
The authors add further:
“While structures of the Harappan civilisation do not have stone pathways leading to the entrance, these two buildings have such pathways. The whole city is inclined 6 degrees to the West of north, but the two circular structures in the Bailey have openings that are exactly to the north and west respectively. In addition, the west-facing structure has two walls that are so constructed that their shadow would just touch the entrance to the structure on winter and summer solstice days.”
According to these two scientists, the the circular structures, out of this complex 13 room structure, were designed for non-residential purposes. The exact purpose of these round structures was to find precisely the days of summer and winter solstice. Before we can understand, how these structures were used by Dholavira people, let us first note some interesting facts. The city of Dholavira is on the Tropic of Cancer (latitude 23d 26′ 22”). The location of this structure is latitude 23d 53′ 14.0” N; 70d 12′ 44.5”. However the earth’s axis of rotation fluctuates by about 0.5d over centuries and hence, we can assume that Dholavira lay exactly on the Tropic of Cancer. Hence the shadows of all the structures would be to the north of the structure on all days except for the local solar noon of Summer Solstice, when the Sun would come to the zenith and no shadows would be cast.
These two circular structures probably had a flat roof with an circular opening. Authors say that a bright spot of light would fall on the floor along with its shadow. By interpreting this image and shadow, Dholavira people could exactly find out the days of summer and winter solstice and using their staircase calender, would know about the month, phase of the moon and the day.
(image may be copyrighted)
The second important information that would have been required was the precise knowledge of the directions, without which sailings would have been impossible. Since there were no magnetic compasses those days ( magnetic compass was discovered only around 200-300 BCE) they had to depend for directions on stars or in particular the Polar star. Due to precession of the equinoxes,around 2000 BCE, the polar star was a weak star identified as “Thuban” today.
The authors observe:
“ Unlike all other regions, the Bailey area rises from South to North with an estimated inclination of 23.5d which corresponds to the latitude of the place. Hence standing at the southern end of the Bailey, the celestial North Pole would be seen at the top of the slope.
At the southern end of the Bailey structure are two deep square pits with no steps for entry which would be ideal to observe stars close to the azimuth even in the presence of light pollution, some amount of which would have existed even in those times.”
It would be clear that if an observer stood in one of the pits at night and looked towards north along the north-south slope of the ground in Bailey, he would have always seen “Thuban,” and would have known the true north direction on any night.
All the readers would agree that possibility of an astronomical observatory in Dholavira, as conceptualized by these two scientists, is absolutely an exciting and fascinating facet of this civilization and only shows how vibrant this civilization really was. In next part, I shall briefly touch upon the life style and religion of these people.
(First Published in Akshardhool on 6 March 2013)