BOOK
Indian Astronomy: An Introduction
M S Sriram
Indion Astronomy An Introduction
S Balachandra Rao
Universities Press, Hyderabad
2000, Price: Rs 190, pp.207
India has had a vibrant tradition in astronomy
from the Vedic times down to the present
day. There are references to the names of the
lunar months, intercalary months (adhikamasas) and the seasons (ritus) which are based
on the motions of the Sun and Moon, in the
Vedas. Names of prominent stars are also
listed in Taittareeya Brahmana. Vedanga
Jyotisha composed around 12th -14th century
BC is a text exclusively devoted to astronomy.
A calendar system is explicitly formulated in
this text. There are no major works in
astronomy available from that time until 499
AD when Aryabhateeya was composed, though
there are references to earlier works in
Varahamihira's Panchasiddhantika. The
Siddhantic tradition of mathematical astronomy in India begins with Aryabhateeya of
Aryabhata and continues till the end of the
19th century, Siddhantadarpana by Chandrasekhara Samanta, being the last major work.
The Siddhantas are exclusively devoted to
astronomy and give explicit algorithms for
calculating the positions of the Sun, Moon
and planets, and also for daily phenomena
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associated with the diurnal motion of the
Sun. Details relating to calendar and eclipses
are also given in them.
Very little is known about these works among
the general public, though the Indian calendar
is extensively used even now for religious and
social purposes. Most educated people do not
have even a faint notion of what these
Siddhantas and other works in Indian astronomy contain. This is understandable considering the fact that there are hardly any
books which give a simple account of the
contents of these texts. English translation of
some major texts like Aryabhateeya, Suryasiddhanta and Siddhanta Shiromani, etc. with
explanations in modern notation are available
(though not always easily accessible).
However, these are all meant mainly for a
research scholar in the area or an expert, and
are hardly suitable for an intelligent laymen
who is eager to learn the subject but does not
want to spend several months on them. It is
in this context that the book 'Introduction to
Astronomy' by S Balachandra Rao is very
relevant and welcome. In the words of the
author, the present book on Indian Astronomy
is designed mainly for the benefit of students
and general readers. The purpose of the book
is not only to create an awareness about Indian
astronomy among the readers, but also to
make them fairly proficient in the concepts,
technicalities and computational procedures
developed by great Indian mathematicians
and astronomers over the past two thousand
years.
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The book begins with a historical introduction in Chapter 1. The basic concepts of
positional astronomy with details of Indian
terminology are explained in Chapters 2, 3
and 4. Chapters 5 and 6 give a detailed
account of the time units in India and of the
traditional Indian calendar. Chapter 7 is on
the mean positions of the Sun, Moon and
planets. These chapters are all lucidly written
and I expect them to be comprehensible even
to a high school graduate with a reasonable
mathematical background. Chapters 8 and 9
give the procedure for the computation of
true positions of planets. However explanations of the procedure for calculating the true
positions are lacking. For instance, it is now
known that the 'Sighra' correction amounts
to the conversion of heliocentric longitudes
to geocentric longitudes. In the absence of
such an explanation, a reader would wonder
about the significance of this correction.
Chapter 10 is on 'Triprasna', direction, place
and time. Here also elucidation of the concepts
of hour angle, lagna, etc., through figures
would have been helpful. Chapter 11 and 12
are on lunar and solar eclipses respectively,
which are the more advanced topics in any
text on positional astronomy. In particular,
calculation of a solar eclipse is a lengthy affair
and involves careful handling of the solar and
lunar parallaxes and many iterative computations. The author's treatment of eclipses is
somewhat sketchy, though he has given
numerical examples to illustrate the
calculational procedures. It would have been
useful if the rationale behind the calculations
were given in more detail.
The book gives listings of computer programs
for calculating longitudes of planets and
eclipses based on Suryasiddhanta, as
developed by the author. These would be of
interest to readers inclined towards numerical
computations. It contains a bibliography of
primary and secondary sources of Indian
astronomy. This will be very useful to those
who want to know more about the subject. It
also has a glossary of technical terms in Indian
astronomy as well as an index. The author
should be commended for compiling these
carefully.
On the whole, a person who wants to know
what Indian astronomy is about, will find
this book useful and informative.
M S Sriram, Department of Theoretical Physics,
University of Madras, Chennai 600 025, India.
Not everything that can be counted counts, and not everything
that counts can be counted.
Albert Einstein
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