Page 25 - Guidelines for Training/ Orientation of Faculty on IKS

using śaṅku. Bring out the versatility of this simple device śaṅku in determining a variety of physical
quantities of interest including the latitude of the place. Explain the concept of parallax in general,
and how it introduces an error – that is unavoidable in conducting this experiment for determining
the latitude of the place. Outline the corrections that have been prescribed in the text that would take
into account the above error, as well as the fact that sun is not a point source of light.

11. Determination of the variation of the duration of the day at a given location

Introduce the 6’o clock circle and its significance. Derive the formula for the hour angle at sunset,
and explain how the latitude and the declination of the sun play a role in it. Explain the concept of
cara as outlined in the Indian astronomical texts that captures the variation in the duration of the day
at a given location. Present the formula for determining the local time using shadow measurements.
Also outline how cara plays a role in determining this local time. Bring out the distinction between
this local time and the standard time that we are generally familiar with and generally keep track of.

12. Lagna and its computation
Introduce the concept of lagna, and how non-trivial a problem it is to determine it precisely. Also
point out how this is deeply connected with fixing times for various social and religious functions

such as marriage, etc. Bring out the connection between its computation and the computation of
declination, cara etc. that would have been discussed before. Explain how this can be determined
‘reasonably’ accurately using interpolation. Also outline more precise formulations that have been
given by later astronomers by introducing the notion of kālalagna.

13. Eclipses and their computation

Briefly explain the phenomenon of lunar and solar eclipses, and the crucial role played by the position
of the lunar nodes in their computation. Also bring out how difficult it is to precisely determine the
position of the nodes—as they are not physical objects available for observation. Explain how the
latitude of the moon is computed, and then outline the procedure for the determination of the semi-
diameters of the eclipsing and the eclipsed bodies. Derive the simple formula for determining the

duration of eclipses as well as the obscuration. Also mention that iterative procedures are followed to
improve accuracy. Point out the role of parallax in the determination of solar eclipses.

Suggested References:

1. S. N. Sen and K. S. Shukla, History of Astronomy in India, 2 Ed., INSA, Delhi, 2001.
nd
2. S. Balachandra Rao, Indian Astronomy An Introduction, Universities Press, Hyderabad, 2000

3. History of Astronomy: A Handbook, Edited by K. Ramasubramanian, Aniket Sule and
Mayank Vahia, SandHI, IIT Bombay, and T.I.F.R. Mumbai, 2016.

4. B.V. Subbarayappa and K.V. Sarma, Indian Astronomy: A Source Book, Nehru Centre,
Bombay, 1985.

5. Tantrasaṅgraha of Nīlakaṇṭha Somayājī, Translation and Notes, K. Ramasubramanian and
M. S. Sriram, Hindustan Book Agency, New Delhi, 2011.

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Guidelines for Incorporating Indian Knowledge in Higher Education Curricula