Surya Siddhanta
The Surya Siddhanta (IAST: Sūrya Siddhānta; lit. ‘Sun Treatise’) is a Sanskrit treatise in Indian astronomy, attributed to Lāṭadeva, a student of Aryabhatta I, by al-Biruni,, and dated to somewhere between the end of the 4th and 9th centuries, and comprises fourteen chapters. The Surya Siddhanta describes the authors rules, within a Geocentric model, to calculate the motions of the sun, moon, mercury, venus, mars, jupiter and saturn, along with his estimate of their diameters, and the circumference of their assumed circular orbits around the earth. The text is known from a 15th-century CE palm-leaf manuscript, and several newer manuscripts. It was composed or revised probably c. 800 CE from an earlier text also called the Surya Siddhanta. The Surya Siddhanta text is composed of verses made up of two lines, each broken into two halves, or pãds, of eight syllables each.
The second verse of the first chapter of the Surya Siddhanta attributes the words to an emissary of the solar deity of Hindu mythology, Surya, as recounted to an asura called Maya at the end of Satya Yuga, the first golden age from Hindu texts, around two million years ago.
The text asserts, according to Markanday and Srivatsava, that the Earth is of a spherical shape. It treats Earth as stationary globe around which then Sun and other planets orbit, and makes no mention of Uranus, Neptune and Pluto. It calculates the Earth’s diameter to be 1,600 Yojana (That unit has been estimated as between 8 - 15 km, offering: 12,800 to 24,000 km, verses the known: 12,756 km), the diameter of the Moon as 480 Yojana (3,840 - 7,200 km, verses the known: 3,475 km), and the Sun as 6,500 Yojana (52,000 - 97,509 km, verses the known: ~ 1,392,000 km) and the distance between the Moon and the Earth to be 51,600 Yojana (412,800 - 774,000 km, verses the known elliptical range: 221,500–252,700 miles (356,500–406,700 kilometres). The text is known for some of the earliest known discussions of fractions and trigonometric functions.
The Surya Siddhanta is one of several astronomy-related Hindu texts. It represents a functional system that made reasonably accurate predictions. The text was influential on the solar year computations of the luni-solar Hindu calendar. The text was translated into Arabic and was influential in medieval Islamic geography. The Surya Siddhanta has the largest number of commentators among all the astronomical texts written in India. It includes information about the mean orbital parameters of the planets, such as the number of mean revolutions per Mahayuga, the longitudinal changes of the orbits, and also includes supporting evidence and calculation methods.
