Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is similar, but deals with the electronics side of aerospace engineering. Aeronautical engineering was the original term for the field. As flight technology advanced to include craft operating in outer space (astronautics), the broader term "aerospace engineering" has come into common use. Aerospace engineering, particularly the astronautics branch is often colloquially referred to as "rocket science".