Astronomers & Astrophysicists study the solar system, stars, galaxies, and space using principles of physics and mathematics. Their work adds to the basic scientific knowledge about the nature of the universe and also provides a basis for improvement in such areas as aircraft navigation and satellite communication. They study planets, stars, novas, and colliding gasses between stars in an attempt to find out how they were formed, what they are made of and how they change. They measure light; radio and x-ray emissions from space sources and plot paths for man made satellites and space probes. Currently, the United States has a shortage of  Ph.D. level astronomers.