The British Royal Aeronautical Society identifies the aspects of Aeronautical Art, Science and Engineering" and "the profession of Aeronautics." While the term originally referred solely to operating the aircraft, it's since been expanded to incorporate technology, business, and other aspects associated with aircraft. The term "aviation" is usually used interchangeably with aeronautics, although "aeronautics" includes aircraft like airships, and includes ballistic vehicles while "aviation" technically doesn't. A significant part of aeronautical science may be a branch of dynamics called aerodynamics, which deals with the motion of air and therefore the way that it interacts with objects in motion, such as an aircraft. Aeronautical engineering covers the planning and construction of aircraft, including how they're powered, how they're used, and the way they're controlled for safe operation.