Candravakyas

Chandravākyas (IAST: Candravākyas) are a collection of numbers, arranged in the form of a list, related to the motion of the Moon in its orbit around the Earth. These numbers are couched in the katapayadi system of representation of numbers and so apparently appear like a list of words, or phrases or short sentences written in Sanskrit and hence the terminology Chandravākyas. In Sanskrit, Chandra is the Moon and vākya means a sentence. The term Chandravākyas could thus be translated as Moon-sentences.

Vararuchi (c. 4th century CE), a legendary figure in the astronomical traditions of Kerala, is credited with the authorship of the collection of Chandravākyas. These were routinely made use of for computations of native almanacs and for predicting the position of the Moon. The work ascribed to Vararuchi is also known as Chandravākyāni, or Vararucivākyāni, or Pañcāṅgavākyāni.

Madhava of Sangamagrama (c. 1350 – c. 1425), the founder of the Kerala school of astronomy and mathematics, had set forth a revised set of Chandravākyās, together with a method for computing them, in his work titled Venvaroha.

Chandravākyas were also popular in Tamil Nadu region of South India. There, the astrologers and astronomers used these vākyās to construct almanacs. These almanacs were popularly referred to as the Vākya-pañcāṅgas. This is used in contrast to the modern mode computation of almanacs based on parameters derived from astronomical observations. These modern almanacs are known as Dṛk Pañcāṅgas ( or Thirukanitha Pañcāṅgas).

The Parahita system of astronomical computations introduced by Haridatta (ca. 683 CE), though simplified the computational processes, required long tables of numbers for its effective implementation. For timely use of these numbers they had to be memorised in toto and probably the system of constructing astronomical Vākyas arose as an answer to this problem. The katapayadi system provided the most convenient medium for constructing easily memorable mnemonics for the numbers in these tables. Chandravākyās ascribed to Vararuci are the earliest example of such a set of mnemonics. The period of Vararuci of Kerala tradition has been determined as around fourth century CE and the year of the promulgation of the Parahita system is known to be 683 CE, Vararuci's Chandravākyās should have been around at the time of the institution of the Parahita system.

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