The Surya Siddhanta (“System of the Sun”) is a Sanskrit astronomical treatise regarded as one of the foundational texts of classical Indian astronomy (jyotisha). The text presents a mathematical model of the motions of the sun, moon, and planets, provides methods for computing eclipses and planetary positions, and introduces trigonometric functions - particularly the sine - in a form that some scholars argue influenced both later Indian mathematicians and, through transmission, medieval Islamic and European astronomy.¹⁾ The date of the text's composition is contested; estimates range from roughly the 4th to the 10th century CE, with many scholars identifying a core text and later layers of interpolation. The text is framed as divine revelation, delivered by the sun-god Surya to the astronomer Maya Asura.

The Surya Siddhanta models the cosmos using a system of great cycles (kalpas and yugas) within which planetary motions repeat. It provides mean and true positions of the planets using epicyclic and eccentric-circle methods that some scholars describe as broadly comparable to those of Ptolemaic astronomy, though the relationship between these traditions remains a matter of scholarly debate. The text gives values for the length of the sidereal year, the diameter of the earth, and the distances of the planets that are, by modern standards, accurate to varying degrees. It introduced the sine function (jya) as a computational tool, along with versine and cosine, in a form that became standard in later Indian mathematical astronomy.

The text's cosmological framework is geocentric in structure: the earth is stationary at the center, and the planets move around it. Some modern interpreters have argued that certain passages imply a heliocentric or heliocentric-adjacent understanding; this is a minority interpretive position discussed at Surya Siddhanta - Heliocentric Interpretation Viewpoint.

The Surya Siddhanta survives in a recension that was commented upon by Paramesvara (c. 1380-1460 CE) and later edited and translated into English by Ebenezer Burgess (1860). The question of how much the surviving text reflects an original composition versus accumulated revision is unresolved. The astronomer Aryabhata (born 476 CE) appears to have known an earlier version, which places at least a core text before the late 5th century. For fuller treatment, see Surya Siddhanta - History.

Scholars have debated the extent to which the Surya Siddhanta reflects independent Indian development versus transmission from Hellenistic astronomy. The presence of structural similarities to Ptolemaic methods, as well as Greek loanwords in related texts, has led some scholars to argue for significant Hellenistic influence. Others maintain that Indian astronomy developed the relevant methods independently or adapted external inputs into a distinctly Indian framework. This debate bears on broader questions about the transmission of scientific knowledge in the ancient world and is addressed at Surya Siddhanta - Debate.

There is broad scholarly consensus that the Surya Siddhanta is a geocentric text using epicyclic planetary models, and that it was a major source for later Indian astronomers. Consensus on dating, the degree of Hellenistic influence, and the interpretation of specific passages is weaker. See Surya Siddhanta - Astronomy Consensus and Surya Siddhanta - History Consensus.

• Geocentric model as authoritative - Traditional Hindu astronomical interpretation treats the Surya Siddhanta's geocentric framework as religiously and scientifically normative. See Traditional Geocentric Viewpoint.
• Heliocentric reinterpretation - A minority of interpreters, drawing on specific passages, argue the text encodes or implies a heliocentric model. This view is examined in relation to broader Hindu cosmological claims at Heliocentrism - Hindu Viewpoint and Surya Siddhanta - Heliocentric Interpretation Viewpoint.
• Hellenistic transmission - Some historians of science argue the Surya Siddhanta's methods derive substantially from Hellenistic astronomy. See Hellenistic Influence Viewpoint.
• Indigenous development - Others argue for substantial or complete indigenous Indian origin of the text's mathematical methods. See Indigenous Development Viewpoint.

• Surya Siddhanta - History
• Surya Siddhanta - Debate
• Surya Siddhanta - Astronomy Consensus
• Heliocentrism - Hindu Viewpoint
• Jyotisha
• Aryabhata
• Ptolemaic Astronomy

1. Burgess, Ebenezer, trans. Translation of the Surya-Siddhanta: A Text-Book of Hindu Astronomy. Journal of the American Oriental Society 6 (1860): 141-498.
2. Pingree, David. “History of Mathematical Astronomy in India.” Dictionary of Scientific Biography, vol. 15 (1978): 533-633.
3. Kim Plofker. Mathematics in India. Princeton University Press, 2009. pp. 71-77, 217-219.
4. Neugebauer, Otto, and David Pingree. The Pancasiddhantika of Varahamihira. Copenhagen: Munksgaard, 1970.
5. Aryabhata. Aryabhatiya. Trans. Walter Eugene Clark. Chicago: University of Chicago Press, 1930.