Galileo's work fundamentally differed from his predecessors in that he relied on empirical observation and experimentation using improved instruments, rather than on pure logic or philosophical reasoning alone. Unlike earlier astronomers who mainly used theoretical models and logical arguments to understand the sky, Galileo built a more powerful telescope and made direct observations of celestial phenomena such as the moons of Jupiter, the phases of Venus, sunspots, and the irregular surface of the Moon. These observations provided concrete evidence that challenged the prevailing Earth-centered (geocentric) model and supported the heliocentric model, where planets orbit the Sun
. In summary, the key fundamental difference was Galileo's use of instruments and experiments to observe nature directly, which marked the beginning of modern scientific astronomy and the scientific method, moving beyond the reliance on abstract reasoning that characterized his predecessors' approach.
