Jupiter was first viewed through a telescope in 1610 by Italian philosopher and scientist Galileo Galilei. Until that time, the dominant world view, which was developed by 2nd-century Alexandrian astronomer Ptolemy, held that all of the stars and planets move in orbits around the earth. Galileo, however, observed four satellites, or moons, in orbit around Jupiter. This simple observation of astronomical objects in orbit about another astronomical object other than the earth touched off what is known as the Copernican revolution, named after Polish astronomer Nicolaus Copernicus. Copernicus had earlier developed a cosmology in which the earth orbits the sun, which is now known as the Copernican System. The Copernican revolution was one of the key elements of the Renaissance and the Age of Enlightenment that continues to influence thinking to the present day. The moons that Galileo saw were collectively named the Galilean moons in honor of their discoverer.