The Aryabhatiya of Aryabhata (CE 476–5500 is one of the most important texts in the history of Indian mathematics and astronomy. He composed this work at the age of 23. Here are some of his noted achievements that are found in Aryabhatiya: 1. Aryabhata asserted that the Moon and planets shine by reflected sunlight and that the orbits of the planets are ellipses. 2. He also correctly explained the causes of eclipses of the Sun and the Moon. 3. His value for the length of the sidereal year at 365 days 6 hours 12 minutes 30 seconds is only 3 minutes 20 seconds longer than the true value of 365 days 6 hours 9 minutes 10 seconds. 4. He estimated the value of 'Pi' as : "Add four to one hundred, multiply by eight and then add sixty-two thousand. The result is approximately the circumference of a circle of diameter twenty thousand. By this rule the relation of the circumference to diameter is given." In other words, Pi=62832/20000 = 3.1416, correct to four rounded-off decimal places. 5. Aryabhata accurately calculated the Earth's circumference as 24,835 miles, which was only 0.2% smaller than the actual value of 24,902 miles. This approximation remained the most accurate for over a thousand years.