Galileo Galilei
Galileo Galilei was born on February 15, 1564 in Pisa, Italy. At age twenty, Galileo noticed a lamp swinging above him while he was in a cathedral. Curious to find out how long it took the lamp to swing back and forth, he used his pulse to time large and small swings. Galileo discovered something that no one else had ever realized: the period of each swing was exactly the same. The law of the pendulum, which would eventually be used to regulate clocks, made Galileo instantly famous. After learning of the invention of the spyglass in Holland, Galilei built a telescope of his own, which had a magnification factor of 20. With this, he found mountains and craters on the moon, discovered that the Milky Way was composed of stars, and discovered the four largest moons of Jupiter.