On a
day, sometime in fourth century AD; a learned Hindu mathematician and
scholar, gave finishing touches to a treatise on Astronomy, that is
still being read and referred, even after fifteen hundred years. The
book compiled together, the knowledge and wisdom about Astronomy,
measurement of time and the yearly calender which was of paramount
importance to agriculture. The information had been collected over
thousands of years by ancient sages and scholars. In the preceding
centuries, new ideas had come from China in the east and Greece from
the west. The new Treatise not only took cognizance of these ideas
but incorporated some of them in the text. To make the book more
respectable and acceptable, the learned author decided to claim in
opening verses of the book that the knowledge has come from the Sun
God himself and aptly called his book as ‘Surya Siddhaanta’ or
the ‘Sun God’s commandments’.
Eighth
chapter of this book, maps the night sky precisely in Twenty One
verses. Each verse consists of just two lines. This chapter pin
points not only the twenty seven or twenty eight Asterisms or
‘Nakshatraas’ that lie along the passage of The Sun in the sky,
but also include all other major stars that could be seen with naked
eye. The method adapted is unique and is independent of any ground
reference points. This made the system universal and unrelated to
time and place of measurement. The author has also described the
rudimentary apparatus, that could be used for taking these
measurements.
We all
know that for defining two dimensional position of any point object, we need to
specify two numbers, which are called co-ordinates of the point, with
reference to some fixed reference line or axis. In a simple graph,
these reference axis are called the X and Y axis and distances of any
point from these two axis can pin point the position of that point.
But in the sky, there are no fixed lines of reference. We however
know that The Sun and all other planets including Moon, follow a
fixed path in the sky as they move every day and night in an apparent
motion around the earth. This path is seen as a curved line from
earth and is called an ‘Ecliptic. Amazingly, ‘Surya Siddhaanta’
uses this curved line as the reference line for measurements of
positions of ‘Asterisms’. A great celestial meridian or a
circle which passes through the ecliptic poles and the star, whose
position is to be specified, is imagined in the sky. The point of
intersection of this meridian circle and the Ecliptic is considered
as the projection of this star on the Ecliptic. ‘Surya Siddhaanta’
specifies for each star two angular measurements to pin point it
precisely.
First
of these two measurements, is called the ‘Vikshepa’ or Latitude
of the star. It is just the angular measurement between the Star
itself and it’s projection on the Ecliptic. The second co-ordinate
is called ‘Dhruvaka’ or the Longitude and it is the angular
measuerment between projection point of the star on the Ecliptic and
a zero point specified on the Ecliptic itself. Thus with two simple
measurements, which can be done with very rudimentary ground
instruments, positions of all the stars can be pin pointed. The
system of measurements is extremely simple and does not require any
ground reference points. Devised in an era, when there were no
telescopes, no sextants for angle measurements or even writing paper
was not in common use, the method was of immense value. Further the
observations could be narrated in simple Verses so that everyone
could remember them with ease.
The
Zero point on the Ecliptic was called the ‘First point of the
Aries’ and was actually the point on the Ecliptic, which the Sun
occupied at the time of ‘Summer Equinox,’ when the treatise was
completed. Unfortunately, the authors of ‘Surya Siddhaanta’ did
not consider the Precession of Equinoxes, either due to ignorance or
on purpose and the position of this zero point drifted away from
Summer Equinox point.
This
peculiar way of fixing zero point remains embedded in a mire of
controversies. Rev. Ebenezer Burgess, who translated this treatise in
English for the first time in year 1860, defines this zero point as a
point 10 minutes eastward of the star Zeta Piscium. Whereas, Calender
committee appointed by Government of India, fixes this point exactly
hundred and eighty degrees from position of star Chitra or Spica.
Another study taken up later, fixes this zero point at two hundred
and forty degrees west of star Mula or Lambda Scorpii and says that
the Sanskrit word ‘Muladharma’ has originated from this.
This
ignorance of Precession of Equinoxes, in fact gives us a powerful
tool to fix up the date on which this treatise was completed. Rev.
Burgess fixes it as year 560 AD. The calender committee concludes
that the date must be in year 285 AD. An independent study fixes this
date as 238 AD. We can therefore presume that the great treatise was
completed sometime in third to sixth century AD.
There
are also controversies regarding accuracy of star co-ordinates. Rev.
Burgess and early English scholars have compared the co-ordinates
with latest star charts to point out the differences. Rev. Burgess
has written hundreds of pages not only to high light the errors but
also to justify his view that all knowledge in this treatise has come
from either China or Greece. Even the calender reforms committee of
Government of India, does mention the difficulties faced by them
because of the inaccuracies in the book. But to my mind, all these
controversies are irrelevant and besides the point. We have all the
latest methods of observation, measurement and calculations. What
could be achieved by comparing our observations with those, taken
with naked eyes and with most rudimentary apparatus for measurement
of angles and time.
It is
more important to appreciate the genius of ‘Surya siddhaanta’,
which gave us a method of charting the stars and a method of time
keeping, which even today forms the basis of Hindu Luni-solar
calender and see how the methods and principles described in this
treatise could be put to possible use and applications today.
12
March 2013
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