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 27^1/₃  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.