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.
[2] Vararuchi (c. 4th century CE), a legendary figure in the astronomical traditions of Kerala, is credited with the authorship of the collection of Chandravākyas.
683 CE), though simplified the computational processes, required long tables of numbers for its effective implementation.
[1] 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.
There is a set of 2075 Vākyas called Samudra-vākyas or Maṇḍala-vākyas or Kujādi-pañcagraha-mahāvākyas relating to the motion of the five planets Kuja (Mars), Budha (Mercury), Guru (Jupiter), Bhrigu (Venus) and Sani (Saturn).
It takes the Moon longer to return to the same position, perigee or apogee, because it moved ahead during one revolution.