Pandit Jagannath Samrat (1652–1744), also known as Samrata Jagannatha, is a religious preceptor and astronomer. It is believed that Pandit Jagannath Samrat hailed from a Brahmin family in Maharashtra and was discovered by Jai Singh in 1702 or 1703 CE. Pandit Jagannath Samrat encouraged Raja Savai Jai Singh of Jaipur (Rajasthan) in his pursuit of practical and observational astronomy. Jai Singh had a very long association with him.
Pandit Jagannath Samrat besides his expertise in Hindu astronomy and Sanskrit, was proficient in Arabic and Persian. Among the significant works on astronomy and mathematics composed by Jagannatha, the most important and popular one is Siddhanta Samrat or Siddhanta Sara Kaustubha. The text seems to have been composed after 1730 CE.
It is based on Nasir al-Din Al-Tusi’s version of Ptolemy’s Almagest. Samrat Siddhanta has 13 chapters, 141 sections and 196 illustrations. Pandit Jagannath Samrat has appended a supplementary text of four chapters to the former. This supplementary text is in the traditional Siddhantic style, comprising Yantradhyaya, Jyotpatti, Triprasnadhyaya, Madhyamadhikara, and Spastadhikara. In Yantradhyaya, Jagannatha describes the instruments used in Jai Singh’s observatories – nadivalaya (also called samrat yantra), gola yantra (armillary sphere), digamasa, dakshinottara bhitti yantra, sasthamasa yantra and sarvadesiya jarakali yantra (Zarquali astrolabe).
Pandit Jagannath Samrat’s other famous work, on geometry, is Rekhaganitam. A Sanskrit translation of the Arabic version of Eculid’s famous Stoicheia (Elements), the text has fifteen chapters dealing with topics like plane geometry, theory of numbers and solid geometry. There is a small work called Yantra Prakara by Jagannatha on the instruments used in Jai Singh’s observatories.
Source - Encyclopedia of Hinduism Volume IX - IHRF