Before Galileo, retrograde motion was explained by epicycles. Copernicus was the first to suggest that the earth revolved around the sun, but Galileo provided hard evidence of a heliocentric model with retrograde motion. We know now that the closer a planet is to the sun, the faster it moved around it. Before our time though, this wasn’t known, and astronomers had to use minimal equipment, basic knowledge, and lots of logic to research to stars. At least in Galileo’s time they knew that when objects were closer, they appeared larger, and when an object is farther away, it appears smaller. He also realized that if there is less of something, that could mean that something else is cover it up. When Galileo looked at the sky and saw that each night, Venus was getting larger,and smaller, and looking like there was less or more, he came to the conclusion that the earth was part of a heliocentric solar system. He did this because he knew that Venus’ actions could be explained by the knowledge the people of the time possesed. He knew that Venus could be getting closer and further away from the earth if it was rotating around the sun. He also knew that this would work best if Venus moved around the sun faster than the Earth. He also realized that when it looked like there was less of Venus, this could be Venus was positioned where the sun didn’t shine on all of it from Earth’s point of view. The explanations that Galileo put to his observations strongly supported a