Electromagnetic radiation, also called light even though it is not always visible, is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves to gamma rays. Electromagnetic radiation radiation carries energy and momentum, which may be imparted when it interacts with matter.