Dear Jean,
Thank you for the Thibaut reference. It seems indeed easier to explain the differences using an accretive model. Especially since a sidereal month is 27.3 days, 27 may be a nice rounded number, and Abhijit was added later to account for the remainder. Furthermore, in the unequal nakṣatra system Abhijit was always made very small both in terms of measurement of arcs on the ecliptic and the duration traversed by the Moon. I am however cautious and I try to imagine in my head a pūrvapakṣa trying to explain how 28 could have become 27 instead!
Using VJ as a historical point of reference is not so easy. As Pingree and others have pointed out (Pingree, jyotiḥśāstra, 1981), there are evidences that there are layers of astronomical materials from different periods, and for other philological reasons he dated VJ to 400 B.C. Astronomically speaking, one finds in VJ the 27 nakṣatras beginning with Kṛttikā as in the Vedic saṃhitās. But then they were used not as constellations, but equal divisions of 13;20 deg on the ecliptic. More clues of this adaptation may be gleaned from Somākara’s Bhāṣya. Yano ("The Nakṣatra system of the Atharvaveda-Pariśiṣṭa", 2009) pointed out that the initial point of ecliptic coordinate in VJ was placed not at Kṛttikā or as later at Aśvnī, but rather in between at Bharaṇī 10 deg. So there is a handful of information to be disentangled.
Best regards,
Bill
Bill M. Mak
Institute for Research in Humanities, Kyoto University
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