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Were you wondering when was Jupiter discovered? Well, there’s no way to know. Jupiter is one of the 5 planets visible with the unaided eye. If you go outside and Jupiter is up in the sky, it’s probably the brightest object up there, brighter than any star; only Venus is brighter. So the ancient people have known about Jupiter for thousands of years, and there’s no way to know when the first person noticed the planet.
Perhaps a better question to ask is, when did we realize that Jupiter was a planet? In ancient times, astronomers used to think that the Earth was the center of the Universe. This was the geocentric model. The Sun, the Moon, the planets, and even the stars all orbited around the Earth in a series of crystal shells. But one thing that was hard to explain was the strange movements of the planets. They would move in one direction, then stop and go backwards in a retrograde motion. Astronomers created ever more elaborate models to explain these bizarre movements.
But then in the 1500s Nicolaus Copernicus developed his model of a Sun-centered, or heliospheric model of the Solar System. The Sun was center of the Solar System, and the planets, including Earth and Jupiter orbited around it. This nicely explained the strange movements of the planets in the sky. They were really following a circular path around the Sun, but the Earth was also traveling around the Sun, and this created different speeds based on our perspective.
The first person to actually view Jupiter in a telescope was Galileo. Even with his rudimentary telescope, he was able to see bands across the planet, and the 4 large Galilean moons that have been named after him. The moons clearly were orbiting Jupiter, which broke the theory that everything in the Universe was orbiting the Earth.
With bigger telescopes, astronomers were able to see more details in Jupiter’s cloud tops and discover more moons. But it wasn’t until the space age that scientists got to really study Jupiter close up. NASA’s Pioneer 10 was the first spacecraft to fly past Jupiter in 1973. It passed within 34,000 km of the cloud tops.
We’ve also recorded an entire episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.