There are two main types of astronomers - observers and theorists, although most astronomers are a mix of both. Observers are astronomers who take pictures of the sky through telescopes. These pictures may be taken in ordinary visible light, or they may be pictures of radio waves, or of x-rays, or any other type of light. Some observers even look for high-energy particles called cosmic rays which come from deep space. Theorists are astronomers who try and explain what observers see, and even predict objects that might exist that we have not or cannot see.
Theorists use mathematics and physics to explain how the universe works.
They often use giant, powerful computers to solve complicated math problems. Theorists and observers work together to try and explain everything from the dust that makes up meteors to the structure of the entire universe. They try and explain how stars and galaxies are born, live, and die. As for the history of the planets, I suggest that you look at a web page designed by students at the university of Arizona. Sincerely, Kurtis Williams Back to the Ask An Astronomer page.