During Vedic times, the main objective of astronomy was fixing
dates for ritual animal sacrifices which were held periodically.
However, a lack of written evidence from this period suggests that
the complete story has not been revealed.1
The sky was divided into 27 portions based on the 27-day length
of the lunar cycle. In fact, the lunar cycle lasts almost 271/3
days, thus a 28th portion was later added to correct the error.
Unaided by any telescope, the Indian astronomers knew of seven
members of the solar system - the sun, the moon, Mercury, Venus,
Mars, Jupiter and Saturn. In ca. 100 CE, Bhaskara measured the
diameter of the sun. Ancient astronomers followed the geocentric
theory - that the earth was the centre of the universe - though,
in 497 CE, Aryabhatta suggested that the earth revolved round the
sun and rotated on its own axis.
Indian astronomers were also able to calculate the length of
the year, the lunar month, and many other astronomical measures,
often with greater accuracy than the western civilisations.2
They also explained eclipses and understood their cause.
The Indians used a lunar calendar of twelve months, each around
twenty-nine to thirty days long. The month began and ended with
the full moon (the new moon in some parts of the south). Since a
year in this system measured only 354 solar days, the Indians
added an extra month every thirty months to correct the
discrepancy in the month and the season.
By the Gupta age (4th century CE) the Western solar calendar
based on the Roman system was known but the traditional lunar
calendar was, and still is, used for religious purposes. The signs
of the zodiac were also adopted, their names being the literal
translation of their Greek counterparts.
1,2.A.L. Basham, “The Wonder that was
India”, (Sidgwick and Jackson Limited, 1967),p. 490.