Whose first systematic observation of Jupiter’s moons helped overturn the idea that everything orbits Earth?

Galileo Galilei made the landmark observations with a telescope in January 1610 and published them in Sidereus Nuncius later that year. He saw Io, Europa, Ganymede and Callisto—now called the Galilean moons—circling Jupiter. That was powerful evidence against the geocentric model and supported a Sun-centered cosmos. Galileo’s work became one of the foundations of modern observational astronomy.