Grahalāghavaṃ is a Sanskrit treatise on astronomy composed by Gaṇeśa Daivajna (c. 1507–1554), a sixteenth century astronomer, astrologer, and mathematician from western India, probably from the Indian state of Maharashtra.
It is a work in the genre of the karaṇa text in the sense that it is in the form of a handbook or manual for the computation of the positions of the planets.
[2] The work is divided into sixteen chapters and covers all the commonly discussed topics in such texts including planetary positions, timekeeping and calendar construction, eclipses, heliacal rising and settings, planetary conjunctions, and the mahāpāta-s.[2] The most striking features of the work that made it highly popular include its use of an ingenious method to reduce the traditional method of computations involving 'astronomical numbers' to smaller numbers and its meticulous and careful avoidance of the use of the trigonometrical sines by replacing them with simpler, still acceptably accurate, algebraic expressions.
[1] The former is effected by introducing the concept of a new cycle called a cakra, a period consisting of 4016 days which is approximately 11 years.
Traditional computations make use the concept of ahargaṇa which is the number of civil days elapsed since the kali epoch which falls on 17/18 February 3102 BCE.