What is the name of the ancient Indian astronomical text by Brahmagupta that first defined zero as a number?

The ancient Indian astronomical text by Brahmagupta that first defined zero as a number is the Brahmasphutasiddhanta. Written around 628 CE, this Sanskrit work combined mathematical astronomy with important advances in arithmetic and algebra.

Brahmagupta treated zero as a number in its own right, rather than merely as a placeholder or symbol for an empty position. In the text's mathematical chapters, he gave rules for adding, subtracting, and multiplying with zero, as well as operations involving positive and negative numbers. These ideas were a major step toward the arithmetic system used today.

The work also discusses quadratic equations, square roots, sums of series, and methods for calculating astronomical positions. It was written entirely in verse and contains no modern mathematical notation. Its title is often translated as “The Correctly Established Doctrine of Brahma.”

Brahmagupta's treatment was pioneering but not fully modern: he incorrectly stated a value for zero divided by zero and did not resolve division by a nonzero number by zero. Even so, the text remains a landmark in the history of mathematics.