Measuring the earth’s diameter

Brahmagupta (597-668 AD), the mathematician and astrologer from Rajasthan, who was head of the astronomical observatory at Ujjain during his time, is recognised by history for a variety of reasons. For one, he authored the ‘Karana Khandakhadyaka’ – a book on astronomical calculations, and the Brahmasphutasiddhanta’ (taken by the caliph of the Abbasid, Al Mansur, to Baghdad in the 8th century).

In 628 AD, he was the first to recognise gravity as a force of attraction. He believed that “bodies fell toward the center of the earth in proportion to their weight, just as the nature of water is to flow.” Brahmagupta described this gravitational pull of weight in Sanskrit as ‘gruhtvaakarshan’.

Contrary to popular belief that credits Bhaskaracharya as being the first to introduce the concept of zero, it was in fact Brahmagupta who established the basic mathematical rules for dealing with zero1 +0= 1:1 – 0=0:1 x 0 = 0.

He used this mathematical theorem as far back as the 7th century AD to measure the earth’s diameter getting to a figure of 7905 miles, which is amazingly close to today’s calculation of 7918 miles!