Jupiter (1610–1687): Jupiter, the fifth and largest planet of our solar system, has dominated the night sky throughout recorded history. Typically the second brightest planet when viewed from Earth, Venus being the first, Jupiter has held a key position in mythological lore since the time of the Roman Empire. To the Romans, Jupiter was the son of Saturn and the god of the sky and weather. Legend has it that after defeating his father, Jupiter became the king of the gods and held dominion over the fate of humans. In Greek mythology Jupiter was represented as the god Zeus. To the ancient Chinese civilizations Jupiter represented one of the five elements. The 11.86-year orbit of Jupiter also closely matched the twelve lunar cycles in a year and thus held special importance in the Chinese belief of natural cycles. While the planet itself was not discovered in the 17th century, Jupiter would play an important role in the verification of the new theories on the physical laws of the universe that were developing during this time.
Perhaps Jupiter’s greatest contribution to the science of the 17th century would begin centuries earlier with the Greek astronomer Ptolemy’s ideas on the structure of the universe. Ptolemy proposed that the universe was centered on the Earth and that in this geocentric model all other objects orbited the stationary Earth. While the stars, sun, and moon cooperated with this model, the planets presented real challenges to the theory. Jupiter’s path consisted of periods when the planet appeared to be stationary against the backdrop of the night sky as well as periods when it displayed a retrograde, or backward, motion. While other planets displayed more pronounced retrograde motions, especially in the case of Mars (see MARS), Jupiter’s motions would severely challenge the Ptolemaic system. In order to make the obser-