सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

213 in modern astronomy also the phase is measured through the elongation. But the maximum phase in modern astronomy is taken to be unity as could be seen from the formula, for, when EPŜ = 180°, the phase = 1. Thus the phase multiplied by 15 gives approximately the tithi. We shall have occasion to deal with this topic later. (3) Suppose ☾ − ☉ = E°. The number of the tithis elapsed is equal to the quotient in E / 12. Take the remainder r°. It means during the current tithi which has a duration of 12°, r° have elapsed. Let the daily motions of the Moon and the Sun be m and s so that the Moon overtakes the Sun by m − s (expressed in minutes for convenience) during 60 nādīs. The elapsed time of the current tithi in nādīs is given by (r × 60 × 60) / (m − s). But r × 60 × 60 = Seconds of arc of the remainder so that it is said “गतैष्यविलिप्तिकाः”. If it be required to find how many nādīs the next tithi lasts, (12−r)° or (12−r) × 60′ is to be gained by the Moon over the Sun. So the time in Nādīs = ((12 − r) × 60 × 60) / (m − s) = एष्यविलिप्तिकाः / (m − s) . (4) A lunation is again divided into 60 Karaṇas and so 6° of increase in elongation correspond to a Karaṇa. These Karaṇas are eleven in number, out of which 4 are fixed to occur during the latter half of Kṛṣṇa Chautùrdasī, during the two halves of Amāvāsyā and the first half of the Sukla pratipat. Their names are Sakuni, Chatuṣpāt, Nāgava, and Kimstughna. So there remain 56 halves of tithis during the lunation during which the remaining seven Karaṇas, Known as Bava, Bālava etc. rotate eight times. Thus the first half of the duration of any tithi is covered by one Karaṇa and the latter by another. The computations of Karaṇas proceeds as with respect to tithis