Surya Siddhanta has been one of the astronomical Siddhanta which has been worked out by a number of astronomers from time to time. The work of Surya Siddhanta has been summerised in the book Panchsiddhantika within the chapters 9-11, 16, 17. While the Chapter I discusses the Yuga elements of the Sun and the Moon, the chapters 13 to 15 discusses the cosmogony , geography and the relevance of Sun and Moon in Hindu Astronomy. The work of Surya Siddhanta can be traced back till the Buddhist age in 3rd century BC which has preserved and upgraded in every age till it was discussed by Varahamihira in the 10th century BC. This article had been a major text of the Gupta Period where it discusses the true motions of luminaries which confirm their actual position in the Sky; it helps to trace the actual position of several stars other than the lunar Nakshaytra and treats the calculation of solar eclipse.
The old version of Surya Siddhanta which was summarized by Varahamihira had been much different from the present day version of Surya Siddhanta which was developed in 400AD. Surya Siddhanta has been referred by a number of astronomers from time to time which include Aryabhata I also who referred to the text. The text holds the fact which is coming from the version of Varahamihira, that the world has a total of 180,000 years containing 66389 intercalary months and 1, 045, 095 omitted lunar days. This gives 65,746,575 days in a yuga. The comparison which provides an insight in the old and new version of the text say that a period with 180, 000 days can be convertred into a mahayuga of 4,430, 000 years which shall multiply the former with 24 and increase the total numbers of days. In case of planetary revolution too the text reveals the number of changes and the differences which have been marked by Aryabhata. In case of other Astronomical calculations the Modern day version of Surya Siddhanta shows a lot of variations.
The modern day version of Surya Siddhanta was comprised by Lata who is contemporary to Aryabhata I who marked the difference between the basic calculations of Hindu Astronomy. This version is a condensed version of astronomical elements and the calculations which has travelled since ages. The new theory includes 500 verses which are divided into different volumes presented by different scholars conclude that within the planetary motion the planets are attached with each other by cords of air which are stationed in the invisible paths which have been described differently by all the astronomers. The planets are impelled in heir own motions uniformly. The modern Surya Siddhant produces such theories which are much closer to our present day astronomy which define the solar system.
Thus, Surya Siddhanta can be considered as one of the most accurate and current theories on Indian Astronomy.
