Page 24 - Guidelines for Training/ Orientation of Faculty on IKS

6. What is Pañcāṅga?

Division of the celestial sphere/ecliptic into 12 and 27 equal parts — rāśi and nakṣatra division.
Explain their significance by pointing out their basis; that is, they are connected with the duration
of 12 lunar months and the period of moon’s revolution around the earth, and not introduced
arbitrarily. Explain the five elements that constitute Pañcāṅga – and also bring out their astronomical
significance. Also point out that they are essentially different units of time. Illustrate with numerical
examples the computation of these elements in a Pañcāṅga. Explain how to compute the average
period of a lunar month; Bring out the need for the introduction of an adhikamāsa in the calendrical
system. Outline the broad categories into which different calendars that are followed can be put
into— namely solar, lunar and luni-solar.

7. Key concepts pertaining to planetary computations
The revolution numbers of various planets, nodes, apogees, etc.; The count of the number of civil days,

adhikamāsas, etc. in a mahāyuga. Introduce the concept of Ahargaṇa, and its significance; The basis
for choice of epoch. Calculation of Ahargaṇa; Illustration with a few numerical examples choosing
contemporary dates – using siddhāntic text (to begin with). Explain the computation of mean motion of
planets, and how its computation along with the Ahargaṇa can help in finding the mean position of planets.

8. Computation of the true longitudes of planets

Provide an overview of the steps involved in the computation of the true longitudes. Explain manda-
saṃskāra in detail using epicyclic model and eccentric model. Outline the nature of the resultant
orbit, etc, and explain how this correction takes into account the eccentric nature of the planetary
orbit. Emphasise and make the students appreciate the simplification achieved in computation by the
‘constraint’ r/R = r /R. Explain śīghra-saṃskāra in detail; Point out how this correction boils down to the
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transformation of the heliocentric coordinates to geocentric. Also indicate how this simple model takes
care of the retrograde motion of the planets. Bring out the distinction between the inner and outer planets.

9. Precession of equinoxes – sāyana and nirayaṇa longitude

Introduce the concept of precession of equinoxes. Explain solsticial and equinoctial points, and
connect them to the concept of uttarāyaṇa and dakṣiṇāyana in the Indian calendrical system. Derive
the formula for finding the declination of the sun on any day at any time, and also illustrate it with
examples. Also highlight how crucial its accurate computation is for the computation of various other
quantities precisely — including the problem of finding the direction and the latitude of the place —
even if we choose to do them by experimental methods.

10. Finding the cardinal directions and the latitude of a place

Introduce śaṅku (the gnomon), and explain how it has to be prepared as described in the texts.
Describe the experimental set up that has to be made meticulously for conducting experiments with
śaṅku and doing shadow measurements. Explain how with a very simple experiment the directions
at a given place can be easily and precisely determined. Also point out that this experimental method
is very old—described even in the Śulbasūtras. Also outline the theoretical basis for the formula that
has been given for correcting the points marked in connection with determination of the direction

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