For nearly 1,400 years, Claudius Ptolemaeus's (Ptolemy) geocentric model, articulated in the Almagest (c. 150 AD), was the authoritative cosmic blueprint. It placed Earth at the center of the universe, with planets moving on complex paths called epicycles within larger circles (deferents) to explain their observed retrograde motion.

The first major challenge emerged from Nicolaus Copernicus. In his 1543 work, De revolutionibus orbium coelestium, he proposed the heliocentric model. This elegantly explained retrograde motion as a natural effect of Earth itself moving, overtaking other planets in its orbit. While philosophically revolutionary, the Copernican model, still bound by the ancient requirement for perfect circular motion, relied on its own epicycles and was not significantly more accurate than Ptolemy's for predicting planetary positions.

The philosopher Giordano Bruno was an early and passionate defender of the Copernican system, but he took its implications much further. He proposed that the stars were distant suns, each with their own inhabited planets, and that the universe was infinite, denying the finite sphere of fixed stars. For these heretical theological and cosmological ideas, which challenged the very core of Church doctrine, he was tried by the Roman Inquisition and burned at the stake in 1600.
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The revolution was ultimately driven by precise data. In the late 16th century, Tycho Brahe compiled a lifetime of unparalleled naked-eye astronomical measurements. His records, notably of Mars, were accurate to within one arcminute. Tycho himself rejected the full Copernican model, proposing a hybrid Tychonic system where planets orbited the Sun, which in turn orbited a stationary Earth.

Upon Tycho's death, his data passed to his assistant, Johannes Kepler. A firm Copernican, Kepler struggled for years to fit Tycho's observations of Mars into a circular orbit. A mere 8 arcminutes of discrepancy between theory and observation led him to a breakthrough: the orbits were not circular, but elliptical.  This became the first of his Three Laws of Planetary Motion (1609-1619), which provided a simple, accurate, and physically true mathematical description of the solar system, finally shattering the Ptolemaic paradigm and providing the foundation for modern astronomy.

​Concurrently, Galileo Galilei provided observational telescopic evidence. He saw moons orbiting Jupiter, proving that not all celestial bodies revolved around Earth. He also observed the full phases of Venus, which could only occur if Venus orbited the Sun, offering direct visual proof that supported the Copernican. His vigorous public advocacy for the Copernican system, most famously in his book Dialogue Concerning the Two Chief World Systems (1632), brought him into direct conflict with the Catholic Church and led to his trial and house arrest.