How Did Galileo's Discoveries Support the Heliocentric Model of the Universe?

In order to understand how Galileo’s discoveries supported the heliocentric model of the universe, one should first understand what Copernicus’s theory asserted. Copernicus believed that (1) Earth’s center was the center of its gravity and of the lunar sphere, not the center of the universe, (2) all spheres revolve around the Sun and the Sun did not move, (3) Earth rotates on its axis and around the Sun, and (4) the stars only appear to move because of Earth’s motion – they are actually fixed (Brown, nd). Galileo firmly believed that Copernicus’s heliocentric model was right and determined to prove just that.

During his lifetime, Galileo made five major discoveries to support the heliocentric view. He discovered (1) four moons orbiting Jupiter, (2) planets were circular discs not just points of light, (3) Venus exhibited phases like the Moon, (4) there were mountains, craters, plains, and possibly bodies of water present on the Moon, and (5) the Sun had sunspots and it rotates (Tarbuck, Lutgens, Tasa, 2009). These five discoveries marked the beginning of modern astronomy.

The invention of the telescope in 1608 by Hans Lippershey made Galileo’s discoveries possible. Galileo heard about the invention and developed one of his own in 1609 and was the first to use a telescope to study the universe (Cox, 2013). The discovery of four moons orbiting Jupiter was a very big deal because it disproved the idea that everything revolved around the Earth; the main tenet of the geocentric model of the universe.

The discovery that other planets were circular discs instead of points of light was important because it indicated that they must be Earth-like and they were not star-like. The views of the Catholic Church, the geocentric model, held the Earth to be the center of everything and a unique structure – to imply that other planets were just like Earth (or that Earth was just like other planets) was heretical.

Quiet possibly his most important observation was...