How was Aryabhata, the great astrologer of classic age, able to find out the exact Earths circumference?
Aryabhata had collected much data from existing sources by then and much of the leg-work must have been done by then. His work is more cerebral, compiling, collating and formulating into viable theory. Aryabhata’s computation of Earth’s circumference as 39,968.0582 kilometres was only 0.2% smaller than the actual value of 40,075.0167 kilometres. This approximation was a significant improvement over the computation by Greek mathematician Eratosthenes (c. 200 BCE), whose exact computation is not known in modern units but his estimate had an error of around 5–10%. I reproduce here a passage from his Aryabhatiyam (gaṇitapāda 10) a Sanskit verse for calculating ‘Pi’ value: chaturadhikam śatamaśṭaguṇam dvāśaśṭistathā sahasrāṇām Ayutadvayaviśkambhasyāsanno vrîttapariṇahaḥ. “Add four to 100, multiply by eight, and then add 62,000. By this rule the circumference of a circle with a diameter of 20,000 can be approached.” This implies that the ratio of the circumference to the diameter is ((4+100)
