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

12 and on Brahmaguptācharya's verse 12, ch. 20 namely ज्ञातं कृत्वा मध्यं भूयोऽन्यदिने तदन्तरं भुक्तिः त्रैराशिकेन भुक्त्या कल्पग्रहमण्डलानयनम् Aryabhatācharya and his immediate followers Lallā- charya and Vateswarācharya make the yuga-pādas of equal duration. Brahmaguptācharya criticises Aryabhata for having said so against the Canons of the Smṛtis as well as Romaka for having ignored the concept of yugas, manvan- taras and Kalpa, as this he deems as a heresy (Vide verses 9 & 13 ch. I). Indeed there seem to be two schools among the ancient Hindu Astronomers one of Brahmagupta who was followed by Sripati, Bhaskara and a number of others and the other of Aryabhata who was followed by Lalla, Vateswara, Bhas- kara I, and a host of others mostly hailing from Kerala. There is an Aryabhata who has been termed Aryabhata II and who was the author of a book named Brihad-Arya- bhatiyam or Mahā-Siddhanta as it is also called. M. M. Sudhakara Dwivedi mentions in his Ganaka-Tarangani, that this Aryabhata should have existed after the author of Modern Surya Siddhanta. Aryabhata I, Aryabhata II, many of the Kerala astronomers used a different nomenclature to signify numbers, denoting them by letters. Thus one of the distinguishing features of the Kerala school of astrono- mers (not all of them) seems to be to use letters for numbers. One Kalpa = 14 Manvantaras = 14 × 71 yugas + 15 Sandhis in between the Manvantaras each equal to a Krita ie 4 Kalis = 994 yugas + 60 Kalis = 994 + 6 yugas = 1000 yugas = 4320000000 mean Solar years. Bhaskara speaks of Sandhyas and Sandhyamsas each of them equal to 1/12 of the yugapādas. Thus one Kali = 432000 years = 1200 Divyābdas (gods' years each year being equal to 360 Solar years) = 1000 +