Who Discovered Jupiter?

Who discovered Jupiter, the largest of the planets in the solar system? Jupiter has always inspired curiosity. It is one of only five planets that you can see without the assistance of a telescope on a clear night. It has a storm—the Great Red Spot—that has been raging since at least the 17th century. Composed primarily of hydrogen and helium, the planet also has over sixty moons that circle it. One of Jupiter’s moons even appears to have ice on its surface. It has even been explored by spaceships, such as the Pioneer mission. Yet, who was the first person to discover this large planet? Who was the first person that led to the latter curiosity for this great giant?

There actually is no known single person who “discovered” Jupiter. Knowledge of the planets predates telescopes, when ancient civilizations realized that the planets were separate entities from the stars. Jupiter is actually the third brightest object in the sky, so it’s plausible that humans observed it before organized science, or even civilization, was formed.

In the early days of mankind, the planets were often tracked with startling accuracy. Ancient civilizations were able to distinguish the stars from the planets, because the planets moved from night to night. They were designated as “wanderers” by Chinese and Arabic astronomers. In fact, Jupiter’s name originates from the Roman God of Jupiter.

The Greeks named the planet first after Zeus, and this was then translated into the Roman’s name for Zeus, "Jupiter." Both the Greeks and the Romans recognized that, just as Jupiter was the King of all Gods, the planet Jupiter was the King of all planets.

The Romans believed that the planets—bigger and more visible than the stars—exposed secrets about their Gods. However, although ancient civilizations and humans could see Jupiter and they understood that it was in some way different than the stars, man did not really understand that it was a planet until the 16th century.

Understanding of the Solar System

In the 16th century, scientists began to doubt the idea that Earth was at the center of the solar system. Nicolaus Copernicus created a new heliocentric model for the Solar System, which showed the Earth as revolving around the Sun. This caused a controversy with the church, who supported the idea that the universe revolved around Earth.

However, Galileo proved Copernicus’ theory when he observed Jupiter’s moons orbiting the planet using his telescope. Previously, all objects were thought to orbit Earth. If Jupiter’s moons orbited Jupiter, this disproved the notion that Earth was at the center of the universe. Galileo’s observation of Jupiter’s moons was the first known recording of them, and Galileo was the first individual to observe Jupiter using a telescope.

Galileo published his observations about Jupiter in Sidereus Nuncius in 1610, along with his observations about the Moon, and the Milky Way. In this famous book, Galileo sketched sixty-four distinct observations of Jupiter’s moons from January 7, 1610 to March 2, 1610. He calculated the time that he observed the planet and her moons by the hour and minute. Importantly, Galileo was able to realize that the moons weren’t stars—but rather, separate entities circling Jupiter. He made this realization by noting that they weren’t changing position like they should from day to day, if they had been stars.

After Galileo, there were several other astronomers who studied Jupiter and helped discover all that is known today. In the 1660s, Cassini discovered spots and bands on the planet using a telescope. Further, he realized that Jupiter was flat at the poles, and he estimated the rotation period of Jupiter. Cassini further calculated tables to determine the motion of Jupiter’s moons. The Great Red Spot may have been discovered by Cassini as well, although this is disputed. Certainly, by 1831, the spot was known. Heinrich Schwabe drew details of the spot in his sketches.Thus, although the identity of the first individual that observed Jupiter is unknown, Galileo was the first astronomer to truly examine the planet, and certainly each scientist who has studied the planet has helped clarify some of the mysteries of the Great Red Giant.