Galileo’s Discovery

Galileo Galilei learned from observing and measuring what he saw. Galileo was from Pisa, a city on the northwestern coast of the Italian peninsula. In 1583, when Galileo was nineteen years old, he observed a priest swinging an altar lamp. No matter how wide the swing of the lamp, it seemed the time it took to move from one end to the other was always the same. Galileo recognized what scientists today call isochronism and his observations inspired the development of the pendulum clock.

Galileo Builds a Telescope

Galileo’s interest in careful observation soon turned from motion on Earth to the study of the heavens. He had heard stories of a tool that used curved pieces of glass to magnify distant objects. In 1609, after hearing of a Dutch invention, he built his own improved version of the instrument we now call a telescope. In Galileo’s time, Aristotle’s idea of an earth-centered universe was widely accepted. But when the Italian scientist turned his telescope to the night sky, he began to see a universe that did not match the ideas of a Greek thinker who had lived more than 1,800 years earlier.

Challenging Aristotle

Aristotle is still remembered as ‘the Father of Natural Science,’ but in Galileo’s time, his ideas were accepted as fact. He taught that heavenly bodies were perfectly round and smooth. But with his telescope, Galileo saw the rough, cratered surface of the Moon. Galileo also observed that Venus appeared to grow and shrink in a predictable pattern, much like the Moon. Galileo concluded that this would be best explained if Venus orbited the Sun rather than the Earth. Most significantly, he observed moons orbiting Jupiter. This discovery challenged Aristotle’s theory that all heavenly objects revolved around the Earth.

Conflict with the Church

Galileo began to support the ideas of Nicolaus Copernicus, who argued that the Earth and other planets orbit the Sun. While Galileo’s observations did not prove this idea, they did challenge the way many people interpreted the Christian Bible. In 1616, Pope Paul V commanded that the scientist never again ‘defend or hold’ the idea of a heliocentric universe. Though he was a very religious man, Galileo continued to make new discoveries and to support Copernicus’ theory of a sun-centered solar system.