Astrophysics is a science that applies the methods and principles of physics and chemistry in the study of astronomical objects and phenomena including the universe. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—what they are, rather than where they are", which is studied in celestial mechanics. Astrophysics is also used when designing and plotting courses for Spacecraft.