Surya Siddhanta

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The Surya Siddhanta (IAST: Sūrya Siddhānta; lit. 'Sun Treatise') is a Sanskrit treatise in Indian astronomy, attributed to Lāṭadeva, a student of Aryabhatta I, and dated to somewhere between the end of the 4th and 5th centuries by most modern scholars, and comprises fourteen chapters. The Surya Siddhanta describes the author's 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 god, 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 the classical planets orbit. The calculations uses Yojana, a unit estimated as between 8 – 15 km. Though astronomical dimensions had already been estimated with more accuracy by ancient Greek astronomers such as Aristarchus (c. 310–230 BCE) and Eratosthenes (c. 276–194 BCE), Surya Siddhanta calculated the Earth's diameter to be 1,600 Yojana (12,800 - 24,000 km, the known measure being 12,756 km), the diameter of the Moon as 480 Yojana (3,840 - 7,200 km, the known measure being 3,475 km), the diameter...