ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

CHAPTER VI
Indian Luni–
Solar Astronomy
In this chapter, it is proposed to give an account of astrono-
mical constants and the equations in Indian luni-solar astronomy
and to present a comparative view of these quantities with the
corresponding ones in Greek and modern Astronomy. This acco-
unt has been reproduced from P. C. Sengupta's. Appendix I of
the Khaṇḍakhādyaka It has been shown that in many cases
the Indian values of these constants are more accurate than the
Greek values. and in Indian lunar astronomy the equations
or inequalities discovered are the most startling.
Solar Astronomy
In solar astronomy the length of the year was determined
by Āryabhaṭa¹ from the heliacal risings of some bright star at
the intervals of 365 and 366 days.
(1) The year according to the Āryabhaṭīya
= 1577917500 / 4320000 days = 365.2586805 days,
= 365 da. 6 hrs. 12 mins. 29.64 secs.
(2) The same
= 1577917800 / 4320000 days = 365.25875 days.
= 365 da. 6 hrs. 12 mins. 36 secs., according to the
Khaṇḍakhādyaka, the Sūryasiddhānta of Varāha
and the modern Sūryasiddhānta.
(3) It is
= 1577916450 / 4320000 days = 365.2584375 days,
= 365 da. 6 hrs. 12 mins. 9 secs., according to the

1, P. C. Sengupta, "Aryabhata's Method of determining the Mean Motions
of Planets," Bulletin of the Calcutta Mathematical Society. Vol. XII, No. 3.