The Cambridge History of India, Vol. I: Ancient India v1.c17.160

v1.c17.160

On the other hand, a distinct advance was unquestionably made in regard to astronomical knowledge. The Rigveda knows only, so far as we can see, the year of 360 days divided into twelve months of thirty days each, which is six days longer than the synodic lunar year, and nearly five and a quarter days too short for the solar year. To bring the year into something like order, intercalation seems to have been attempted quite early: we hear in a riddle hymn of the Rigveda (I, 164) of the intercalary month, the thirteenth. In the Saṃhitās the system is slightly more developed; and possibly some efforts were being made to arrange intercalation in a cycle of five years in such a manner that the years and the seasons would be made to coincide; but it is fairly clear that a satisfactory method had not yet been obtained. The Saṃhitās, however, give us the names of the twelve months arranged very artificially in six seasons, and they introduce to us the important doctrine of the Nakshatras, or ‘lunar mansions,’ groups of stars selected as roughly indicating the parts of the sky in which the moon appeared in the course of a periodic month of 27–28 days. In the Rigveda the term Nakshatra seems usually to mean no more than ‘star’; and it is only in the admittedly late marriage hymn (X, 85) that the names of two of the Nakshatras proper are found though in altered forms. The number of the Nakshatras is variously given as twenty-seven in the Taittirīya Saṃhitā and the Kāṭhaka lists and usually later, and as twenty-eight in the lists of the Maitrāyaṇī Saṃhitā and the Atharvaveda. As the periodic month has between 27 and 28 days, the variation may be primitive: of the allied systems the Chinese Sieou and the Arabic Manāzil have twenty-eight: the missing star Abhijit in the smaller enumeration may have fallen out for a variety of causes; and it seems easier to assume this than to regard it as a later addition. The use of the Nakshatras offered a simple and effective means of fixing dates by the conjunction of the new or full moon with a particular Nakshatra, and in the Brāhmaṇa period a further step was taken: on some arbitrary basis which we cannot now determine, twelve of the Nakshatra names in adjectival form were chosen to represent the months. It might have been expected that the months represented by these names would be lunar, but they are, as a matter of fact, the twelve months of the traditional year of 360 days. The whole series of the new names is not found until the Sūtra period; but the vitality of the new system is adequately proved by the fact that the old series of twelve given in the Saṃhitās corresponding to the six seasons is practically ignored in the later literature.