Galileo Galilei (1564 to 1642) was an Italian natural philosopher, astronomer, and mathematician who made fundamental contributions to the sciences of motion, astronomy, and strength of materials and to the development of the scientific method. His formulation of inertia, the law of falling bodies, and parabolic trajectories marked the beginning of a fundamental change in the study of motion. His discoveries with the telescope revolutionized astronomy and led to the heliocentric system, and subsequently the wrath of the Church and an Inquisition against him.
In 1608 a patent was submitted by spectacle maker Hans Lippershey for a refracting telescope. Galileo heard about it and, in 1609, built his own version.
He drew the Moon’s phases as seen through the telescope, showing that the Moon’s surface is rough and uneven. He discovered four moons revolving around Jupiter, now known as the Galilean moons. He discovered sunspots and argued that they are on or near the Sun’s surface, and not satellites. He discovered the the phases of Venus and the rings of Saturn. His theory of the tides had proof of the annual and diurnal motions of Earth.
He built an improved compound microscope in 1625 and called it "little eye."
A Galileo thermometer is a sealed glass cylinder containing a clear liquid and floats that rise or fall in proportion to their respective density and the density of the surrounding liquid as the temperature changes. Galileo discovered the principle on which this thermometer is based—that the density of a liquid changes in proportion to its temperature.
Galilean electromagnetism theory is consistent with Galilean invariance which states that the laws of motion are the same in all inertial frames. This is useful for describing the electric and magnetic fields in the vicinity of charged bodies in electrical networks.
An American robotic space probe that studied the planet Jupiter and its moons, as well as several other Solar System bodies, was named after him.