Few individuals have had as profound an impact on science as Italian physicist and astronomer Galileo Galilei, whose groundbreaking inventions and discoveries earned him the title "father of modern science.'' Galileo's innovative, experiment-driven approach to science made him a key figure of the Scientific Revolution of the 16th and 17th centuries, during which he all but disproved the Aristotelian physics and cosmology that had previously dominated the field in Europe.
Experiments in Motion
Among Galileo's contributions to physics is the law of falling bodies, which states that objects fall at the same speed regardless of weight or shape. Through experiments, Galileo countered the pervasive Aristotelian view, which held that heavier objects fall faster. The distance traveled, he calculated, is proportional to the square of the time it took the object to reach the ground. Galileo also first developed the concept of inertia -- the idea that an object remains in rest or in motion until acted on by another force -- which became the basis for one of Isaac Newton's laws of motion.
Geometric and Military Compass
In 1598, Galileo began selling a geometric and military compass of his own design, though the profits were minimal. Consisting of two rulers attached at right angles with a third, curved ruler between them, Galileo's compass, known as a sector, was multifunctional. Soldiers in the military used it to measure the elevation of a cannon's barrel, while merchants employed it to calculate currency exchange rates.
An Improved Telescope
While he did not invent the telescope, the enhancements Galileo made to original Dutch versions of the instrument enabled his empirical discoveries. Early telescopes magnified objects by three times; Galileo learned to grind lenses and eventually created a telescope with a magnifying factor of 30x. With his unprecedentedly powerful telescopes, Galileo was the first to observe the uneven, cratered surface of the moon; Jupiter's four largest satellites, dubbed the Galilean moons; dark spots on the surface of the sun, known as sunspots; and the phases of Venus. The telescope also revealed that the universe contained many more stars not visible to the naked eye.
The Case for Heliocentrism
In the 16th century, Polish astronomer Nicolaus Copernicus became the first scientist to promote a model of the solar system in which the earth orbited the sun rather than the other way around. Galileo's observations discredited the Aristotelian theory of an earth-centered solar system in favor of the Copernican heliocentric model. The presence of moons in orbit around Jupiter suggested that the earth was not the sole center of motion in the cosmos, as Aristotle had proposed. Furthermore, the realization that the surface of the moon is rough proved untrue the Aristotelian view of a perfect, immutable celestial realm. Galileo's discoveries -- including the theory of solar rotation, as suggested by shifts in sunspots -- incurred the wrath of the Catholic Church, which espoused the Aristotelian system. Upon finding him guilty of heresy in 1633, the Roman Inquisition forced Galileo to rescind his support of heliocentrism and sentenced him to house imprisonment. Galileo was still under house arrest when he died in 1642.