While we don't know the exact date of the earliest observations, it's likely that people noticed Jupiter as early as the dawn of civilization.
It's one of the brightest objects in the sky, and ancient cultures around the world, like the Babylonians, Egyptians, and Greeks, had names for it and observed its movement.
The first recorded observations of Jupiter with a telescope were made by Galileo Galilei in 1610. This was a groundbreaking event, as he was the first to observe Jupiter's four largest moons (Io, Europa, Ganymede, and Callisto) and to see that Jupiter wasn't a fixed star, but a planet with its own moons.
