A L Basham

 

"The procession of the equinoxes was known, and calculated with some accuracy by medieval astronomers, as were the lengths of the year, the lunar month, and other astronomical constants. These calculations were reliable for most practical purposes, and in many cases more accurate than those of the Greco-Roman world. Eclipses were forecast with accuracy and their true cause understood."

These were achieved without the help of a telescope. Accurate measurement was made possible by the decimal system of numerals, invented by the Indians.
It is certain that the Vedic Indians knew something of astronomy and that it had a high utilitarian value for them as it did for all peoples of antiquity. 

The Vedic priests had to make careful calculations of times for their rituals and sacrifices, and also had to determine the time of sowing and harvest. Moreover, astronomical periods played an important role in Vedic thought for they were considered to be successive parts of the ever returning cosmic cycle.

The Rig Veda lists a number of stars and mentions twelve divisions of the sun's yearly path (rashis) and also 360 divisions of the circle. Thus, the year of 360 days is divided into twelve months. The sun's annual course was described as a wheel with twelve spokes, which correspond to the twelve signs of the zodiac.