Early Astronomers: Copernicus, Galileo, Kepler, and Newton
The geocentric model wasn't seriously challenged until Nicolas Copernicus who published a report in 1543 suggesting that the Sun, not the Earth, was the center of the Universe (called Copernican heliocentrism). Nicolaus Copernicus (1473-1543) was the first to explain the observed retrograde, looping phenomena of planet motion by replacing previously held theories of geocentrism (Earth being the center of the Universe) with heliocentrism (the Sun being the center of the observable Universe).
However, the Copernican system was also discovered to be flawed as telescopes were developed to see farther into space and astronomers began to grasp the immense scale of time and distance between our Solar System and other objects in our Milky Way Galaxy and the Universe beyond.
Italian physicist and astronomer, Galileo Galilei (1564-1642) used an early telescope and discovered four large moons of Jupiter (Figure 1.33). He also promoted the Heliocentrism Theory that the Sun, not the Earth, was the center of our Solar System. In 1615 he was subjected to the Roman Inquisition for his scientific inquiries. He was forced to publicly recant his beliefs and subjected to house arrest for the remainder of his life. (Note that the Roman Catholic Church eventually accepted his theory and officially forgave him in 1992!)