Sir Isaac Newton, considered by many to be the greatest scientist who ever lived, was born in Woolsthorpe, Lincolnshire, England, on Dec. 25, 1642. A creative boy, he began inventing mechanical devices while still a child.

In 1661, at the age of 19, Newton entered Trinity College at Cambridge University. He graduated with a bachelor’s degree in 1665. Newton intended to continue his studies at Cambridge, but the university was forced to close that summer because a deadly disease, the bubonic plague, had struck England. To escape the plague, Newton withdrew to the safety of his family’s farm in Lincolnshire.

The next 18 months, spent mostly in Lincolnshire, were a time of incredible scientific creativity for Newton. During the “two plague years of 1665 &1666,” he would later write, “I was in the prime of my age for invention & minded Mathematicks & Philosophy more than at any time since.” Historians often refer to this period in Newton’s life as the *annus mirabilis* or *anni mirabilies*, which in Latin means *miracle year* or *miracle years.*

During this period, Newton performed many experiments to investigate the nature of light and color. Using a prism, he demonstrated that white light contains all the colors of the rainbow. Newton used his understanding of light and color to build the first reflecting telescope in 1668.

Newton also invented a branch of mathematics known as calculus. He used calculus to prove Johannes Kepler’s laws of planetary motion. Kepler’s laws had been based on physical observations. Newton’s development of calculus made it possible to supply these observations with a mathematical basis. Working independently of Newton, the German philosopher and mathematician Gottfried Wilhelm Leibniz also invented calculus in the mid 1670’s.

Newton’s greatest achievement during the “plague years” was his discovery of the law of universal gravitation. When Newton thought carefully about motion, he realized that some force must pull the moon toward Earth. Otherwise, why didn’t the moon move in a straight line away from Earth? Newton’s great insight was to recognize that the force that holds the moon in orbit around Earth is the same force that causes an apple to fall from a tree. Newton’s discoveries on the laws of motion and theories of gravitation were published in 1687 in *Philosophiae naturalis principia mathematica *(*Mathematical Principles of Natural Philosophy*).

Newton returned to Cambridge after the plague in 1667. He became a professor of mathematics in 1669. He lectured once a week on arithmetic, astronomy, geometry, optics, or other mathematical subjects. He was elected to the Royal Society in 1672.