4 MEAN LONGITUDE OF A PLANET corresponding to the current mean lunar day, so that the number of mean solar days between S and s' is equal to the number of mean lunar days between A and L. Adding 3179 to the number of elapsed years of the Saka Era, we. obtain the number of solar years elapsed since the beginning of Kaliyuga. Multiplying that sum by 12 and adding to the product the number of months elapsed since the beginning of Caitra, we get the number of mean solar months elapsed since the beginning of Kaliyuga. This number is equal to the number of mean solar months lying between K and S. (See Fig. 1.) Let us denote it by M. When we multiply M by the number of intercalary months in a yuga and divide by the number of solar months in a yuga, we obtain the number of mean intercalary months corresponding to M mean solar months. This number is, in general, made up of a whole number and a fraction. The fraction evidently denotes the fraction of a mean lunar month lying between A and S.¹ When the whole number of mean intercalary months is added to M, we get the number of mean lunar • months lying between K and A. When we multiply that by 30 and add to the product the number of lunar days (tithis) elapsed since the beginning of the current lunar month, we get the number of mean lunar days lying between K and L. Let us denote this number by T. When we multiply T by the number of omitted lunar days in a yuga and divide by the num- ber of lunar days in a yuga, we get the number of mean omitted lunar days corresponding to T mean lunar days. This also, in general, consists of a whole number and a fraction. The fraction evidently denotes the part of a mean civil day lying between L and s.³ When the whole number of mean omitted lunar days is subtracted from T, we get the number of mean civil days lying between K and s. This is, in general, the number of mean civil days elapsed at mean sunrise at Lanka on the given lunar day since the beginning of Kaliyuga. This. number, is known as "ahargana" (literally meaning "a collection of days"). In the above passage, Bhaskara I has called it by the synonym ahnam nicayaḥ. The mean lunar day (madhyama-tithi) may, however, differ from a true lunar day (spasta-tithi) by one, so that the ahargana obtained by the 1 See Sisi, II, iv. 16. 2 If we add the whole number of mean intercalary months as also the fraction, we shall get the mean lunar days lying between K and S. 3 See Sisi, II, iv. 18 (i). 4 If we subtract the whole number of mean omitted lunar days as also the fraction, we shall get the mean civil days lying between K and L.
