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 +