The Sūrya Siddhānta is a Sanskrit treatise in Indian astronomy in fourteen chapters. The Surya Siddhanta describes rules to calculate the motions of various planets and the moon relative to various constellations, and calculates the orbits of various astronomical bodies. The text asserts, according to Markanday and Srivatsava, that the earth is of a spherical shape. It treats earth as stationary globe around which sun orbits – a geocentric model – and makes no mention of Uranus, Neptune or Pluto, since these planets are not visible without telescope. It calculates the earth's diameter to be 8,000 miles (modern: 7,928 miles), the diameter of the moon as 2,400 miles (actual ~2,160) and the distance between moon and earth to be 258,000 miles (now known to vary: 221,500–252,700 miles (356,500–406,700 kilometres). The text is known for some of earliest known discussion of sexagesimal fractions and trigonometric functions.