"The greatest of Hindu astronomers and mathematicians, Aryabhata, discussed in verse such poetic subjects as quadratic equations, sines, and the value of π; he explained eclipses, solstices and equinoxes, announced the sphericity of the earth and its diurnal revolution on its axis, and wrote, in daring anticipation of Renaissance science: “The sphere of the stars is stationary, and the earth, by its revolution, produces the daily rising and setting of planets and stars.” His most famous successor, Brahmagupta, systematized the astronomic knowledge of India, but obstructed its development by rejecting Aryabhata’s theory of the revolution of the earth. These men and their followers adapted to Hindu usage the Babylonian division of the skies into zodiacal constellations; they made a calendar of twelve months, each of thirty days, each of thirty hours, inserting an intercalary month every five years; they calculated with remarkable accuracy the diameter of the moon, the eclipses of the moon and the sun, the position of the poles, and the position and motion of the major stars. They expounded the theory, though not the law, of gravity when they wrote in the Siddhantas: “The earth, owing to its force of gravity, draws all things to itself.”"