Ancient to Modern Day Space Exploration timeline

Ptolemy was an astronomer, geographer, and a mathematician who was born in Alexandria, Egypt. Ptolemy thought the earth was in the center of our solar system (Geocentric). Ptolemy thought that the celestial body's revolved around the "Earth" in a constant speed in small perfect circles on bigger circles this is called the "wheels-on-wheels" system.

Aristotle was a Greek philosopher who thought that the Earth was in the center of all things because he saw no parallax. The meaning of Parallax is the "apparent shift in the position of an object when viewed from different locations".

Copernicus was a polish astronomer who thought that Ptolemy's model of the solar system was complicated and also thought that the sun is in the middle of our solar system (Heliocentric). But Copernicus like Ptolemy used the "wheels-on-wheels" system and thought that planetary motion of planets is in a perfect circle but it turned out that Copernicus's model was slightly better than Ptolemy's and was the "first step in the development of modern models of the solar system".

Galileo was an Italian mathematician,physicist, and astronomer and made great improvements to the newly invented telescope. Galileo was also the one to discover the moons Io, Europa, Callisto, and Ganymede orbiting Jupiter and these moons are named the Galilean Satellites after Galileo. Based on his observations Galileo said that earth was not the only planet that could be orbited and he was right. He also observed Venus has phases similar to Earth's moon. (He supported Heliocentric).