When the Kālacakra-tantra introduces its own astronomical calculations in chapter 1, verse 26, the Vimalaprabhā commentary thereon refers to four existing siddhāntas:1.
Brahma; 2. Saura; 3. Yamanaka; and 4. Romaka. The Vimalaprabhā again names these same four at 1.86, only saying Sūrya instead of Saura. Three of these siddhāntas are of course well known: Brahma, Saura/Sūrya, and Romaka. I have not been able to determine what the Yamanaka siddhānta is.
The editors of the Vimalaprabhā suggest emending Yamanaka to Yavanaka, a reasonable assumption. However, the
two very old palm-leaf manuscripts of the Vimalaprabhā
confirm the spelling yamanaka. Moreover, the Tibetan translations of yamanaka do not support yavanaka. The Shong ston and Jonang Tibetan translations take yamanaka as gcer bu pa, "naked ones." Elsewhere in the Kālacakra-tantra, at 3.169 and 4.217, Tibetan gcer bu translates Sanskrit nagna, confirming the meaning, "naked." The early Gyi jo Tibetan translation also takes yamanaka as gcer bu. This may suggest a Jaina jyotiṣa siddhānta.
However, I do not know of a Jaina jyotiṣa siddhānta, in the full sense of a jyotiṣa siddhānta; meaning giving the movements of the planets, and not just the movements of the sun and moon, as does the Sūryaprajñapti and works following it such as the Jyotiṣkaraṇḍakam. I have considered the Bhadrabāhu-saṃhitā, but at least in the form we have it, this text seems to be ruled out.
Any suggestions would be appreciated.
Thank you,
David Reigle
Colorado, U.S.A.