In modern day astronomy, we know that the Moon orbits the Earth while the Earth orbits the Sun. We also know that the Sun is itself a star that is part of a huge galaxy that is only a tiny piece of a large, expanding universe. We have this knowledge from centuries of observation and studies. Today we have the tools and technology, like NASA, that allow us to discover new things about the universe. The ancient Greeks played an important role in our astronomical thinking of today. The scientists of the classical era in Greece, along with the Egyptians and Babylonians, have laid the foundations of modern astronomy. They charted the patterns of the stars through naked-eye astronomy and hypothesized about the placement of our Earth and its relation to our universe. Their theories have allowed other generations of scientists to continue with these theories that led us to our modern ways of thinking. It is important to understand that these ancient astronomers were not considered scientists, but rather philosophers. The Greeks considered science to be philosophy. They were unique from past, present, and future cultures in many ways, mostly in that they did not let their invented religion determine the way they explained the world. They were extremely rational thinkers. Pythagoras, a Greek mathematician, was the first to create the word cosmos to describe the universe. His followers, called Pythagoreans, used numbers in an effort to explain the universe through the language of mathematics. Most importantly, the Greeks invented cosmology (the study of the large-scale structure and dynamics of the universe) and paved the way for future generations to expand on that knowledge.