Aristotle was a Greek Philosopher who believed that the earth was the center of the solar system. Aristotle is important because he was the fist thinker to try to figure things out about our solar system.  Aristotle's model looked like this.  

Aristarchus was a Greek astronomer, and mathematician. 

 He was famous because he was reported to be the first one to make a heliocentric model of the solar system. He also attempted to measure the distance between the sun and the moon. He is important to us because he was the first to try to measure distance in space, and create a heliocentric model. Today we us a heliocentric model but not his. He still influenced it though. His model looks like this.   

He was famous because he wrote a book about observations of planets over 800 years ago. It is one of the oldest books we have today. The book is called Almagest. his model was also used for 14 centuries. His model looks like this.  

Copernicus was a polish astronomer. He is famous because he made a very complicated model of the solar system. We use his model. His model looks like this. 

Kepler a german mathematician and astronomer. He was famous because he analyzed observation of the planets and then realized that the reacquiring planetary motions to be exactly circular didn't fit the observation perfect. Kepler then tried many different methods to try to make them fit perfect.  He help us figure out the perfect fit of the planets and that is important. His model looks like this.