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.
Dholavira
layout
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 15 and 30 steps. It was easily possible, by using
markers, which probably were shifted every day, to know what day of
the 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.
6
March 2013
