epithet Somayaji is a title assigned to or assumed by a Namputiri who has performed the vedic ritual of Somayajna. So it could be surmised that Nilakantha Somayaji had also performed a Somayajna ritual and assumed the title of a Somayaji in later life. In colloquial Malayalam usage the word Somayaji has been corrupted to Comatiri. Nilakantha Somayaji as a polymath Nilakantha's writings substantiate his knowledge of several branches of Indian philosophy and culture. It is said that he could refer to a Mimamsa authority to establish his view-point in a debate and with equal felicity apply a grammatical dictum to the same purpose. In his writings he refers to a Mimamsa authority, quotes extensively from Pingala's chandas-sutra, scriptures, Dharmasastras, Bhagavata and Vishnupurana also. Sundararaja, a contemporary Tamil astronomer, refers to Nilakantha as sad-darshani-parangata, one who had mastered the six systems of Indian philosophy. Astronomy In his Tantrasangraha, Nilakantha revised Aryabhata's model for the planets Mercury and Venus. His equation of the centre for these planets remained the most accurate until the time of Johannes Kepler in the 17th century. In his Aryabhatiyabhasya, a commentary on Aryabhata's Aryabhatiya, Nilakantha developed a computational system for a partially heliocentric planetary model in which Mercury, Venus, Mars, Jupiter and Saturn orbit the Sun, which in turn orbits the Earth, similar to the Tychonic system later proposed by Tycho Brahe in the late 16th century. Most astronomers of the Kerala school who followed him accepted this planetary model. Works The following is a brief description of the works by Nilakantha Somayaji dealing with astronomy and mathematics. Tantrasamgraha Golasara : Description of basic astronomical elements and procedures Sidhhantadarpana : A short work in 32 slokas enunciating the astronomical constants with reference to the Kalpa and specifying his views on astronomical concepts and topics. Candrachayaganita : A work in 32 verses on the methods for the calculation of time from the measurement of the shadow of the gnomon cast by the moon and vice versa. Aryabhatiya-bhashya : Elaborate commentary on Aryabhatiya. Sidhhantadarpana-vyakhya : Commentary on his own Siddhantadarapana. Chandrachhayaganita-vyakhya : Commentary on his own Chandrachhayaganita. Sundaraja-prasnottara : Nilakantha's answers to questions posed by Sundaraja, a Tamil Nadu-based astronomer. Grahanadi-grantha : Rationale of the necessity of correcting old astronomical constants by observations. Grahapariksakrama : Description of the principles and methods for verifying astronomical computations by regular observations. Jyotirmimamsa : Analysis of astronomy See also Indian mathematicians Indian