Śaṅkaranārāyaṇa

Sankaranarayana (c. 840 – c. 900) was an Indian astronomer-mathematician in the court of Sthanu Ravi Kulasekhara (c. 844 – c. 870 ) of the early medieval Chera kingdom in Kerala. He is celebrated as the author of Laghubhaskariyavivarana or Laghubhaskariyavyakha, a detailed commentary on astronomical treatise Laghubhaskariya by 7th century mathematician Bhaskara I (which in turn was based on the works of the 5th century polymath Aryabhata).

Sankaranarayana is known to have established an astronomical observatory at the port of Mahodayapuram, present-day Kodungallur, in central Kerala. Laghubhaskariyavivarana (Chapter VII) explicitly states that it was composed in Saka Year 791 (corresponding to 869/70 AD). In the second verse of the commentary Sankaranarayana remembers five major predecessors in the field of mathematics (Aryabhata, Varahamihira, Bhaskara I, Govinda and Haridatta), including his possible master Govinda (c. 800 – c. 860 AD).

At the expiry of every ghatika (= 24 minutes), drums were sounded by the soldiers (at different corners of the city of Mahodayapuram, such as certain "Balakridesvara") to announce time.

Mathematical contributions Laghubhaskariyavivarana covers several the standard mathematical methods of Aryabhata I such as the solution of the indeterminate equation [by = ax ± c] (where a, b, and c are integers) in integers (which is then applied to astronomical problems by the author).

Laghubhaskariyavivarana, according to the commentary itself, was composed in the 25th regnal year of king Ravi Kulasekhara.

Date of Laghubhaskariyavivarana Laghubhaskariyavivarana is dated by the author in three methods.

As a Kali Date (when the ruler made enquiries regarding solar eclipse)

"Angartvambara nanda devamanubhir yate dinanam gane" Anga = 6, Rtu = 6, Ambara = 0, Nanda = 9, Veda = 4, and Manu = 14 Order - 6609414 Reverse Order - 1449066 Kali Date - 3967 years and 86 days = 25 Mithuna, Kollam Era 41 = 866 AD

In the Saka Era

"Sakabdah punariha candra randhramuni sankhyaya" Candra = 1, Randhra = 9, and Muni = 7 Order - 197 Reverse Order - 791 (Saka Year) = 870 AD

In regnal years

Meeting of Guru (=Jupiter) and Sauri (=Saturn) in Capa (Dhanu) = 25th regnal year of the king. In the 9th century, these two planets came to Dhanu Rasi simultaneously only in 869 AD.