Ritual

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Astronomy
Like other disciplines of Indian thought, astronomy and its origins
may be genetically related back to the Vedas. The Vedic Aryans
were well acquainted with the natural routine cycles of heavenly
bodies. The vault of the sky, for example, was seen as being
governed by the eternal ordinances of an inherent universal
principle, Rita (literally, the course of things), which determines
the paths and phases of the moon and the planets, the day/night
cycle and occurrences of eclipses.
The Jyotisha Vedanga and the Surya Prajnapati (c. 400 BC-AD 200)
record the earliest Hindu astronomical statements. In early times,
astronomy developed out of pragmatic speculations which were
necessary and therefore of paramount importance for the careful
calculation of appropriate times for rituals and sacrifices. The
important treatises on Indian astronomy were the Gargi-samhita (c.
AD 230), the Aryabhattiya of Aryabhata (AD 499), the Siddhantasekhara
of Sripati, and the Siddhanta-Siromani of Bhaskara II (AD
1114-1160).
By the beginning of the Christian era, a great upsurge in the
astronomical search was formalized in a number of methodical
studies; many works of great importance, such as the five
Siddhantas, of which the Surya Siddhanta is probably the best
known, were compiled and later summarized by the sixth-century
astronomer and mathematician Varaha-Mihira in his Panchasiddhantika
(The Five Astronomical Systems), written about AD 550.
In his outstanding work, the Brihat-samhita (The Great Compendium),
he describes the motions and conjunctions of celestial
bodies and their significance as omens.
The classical period of ancient Indian astronomy is considered
to have ended with Brahmagupta who wrote the Brahmasiddhanta,
in AD 628, and the Khandakhadyaka, a practical treatise on
astronomical calculations, in AD 664. Aryabhata's new epicyclic
theory, and his postulates regarding the sphericity of the earth, its
rotation upon its axis and revolution around the sun, as well as his
formulae for the determination of the physical parameters of
various celestial bodies (such as the diameters of the earth and the
moon), and the prediction of eclipses and the correct length of the
year by means of mathematical calculation, were significant
achievements which anticipated and agree with the modern ideas.
Aryabhata also gave the first fundamental definition of trigonometric
functions and was responsible for pointing out the
importance of zero.