16th and 17th Centuries

The advent of modern science followed the Renaissance and was ushered in by the highly successful attempt by four outstanding individuals to interpret the behavior of the heavenly bodies during the 16th and early 17th centuries. The Polish natural philosopher Nicolaus Copernicus propounded the heliocentric system that the planets move around the sun. He was convinced, however, that the planetary orbits were circular, and therefore his system required almost as many complicated elaborations as the Ptolemaic system it was intended to replace. The Danish astronomer Tycho Brahe, believing in the Ptolemaic system, tried to confirm it by a series of remarkably accurate measurements. These provided his assistant, the German astronomer Johannes Kepler, with the data to overthrow the Ptolemaic system and led to the enunciation of three laws that conformed with a modified heliocentric theory. Galileo, having heard of the invention of the telescope, constructed one of his own and, starting in 1609, was able to confirm the heliocentric system by observing the phases of the planet Venus. He also discovered the surface irregularities of the moon, the four brightest satellites of Jupiter, sunspots, and many stars in the Milky Way. Galileo's interests were not limited to astronomy; by using inclined planes and an improved water clock, he had earlier demonstrated that bodies of different weight fall at the same rate (thus overturning Aristotle's dictums), and that their speed increases uniformly with the time of fall. Galileo's astronomical discoveries and his work in mechanics foreshadowed the work of the 17th-century English mathematician and physicist Sir Isaac Newton, one of the greatest scientists who ever lived.