Electromagnetic waves are not characterized by rarefactions and compressions as mechanical waves are. Electromagnetic waves, including radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays, consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of wave propagation. Therefore, electromagnetic waves do not involve the physical displacement or compression of matter as rarefactions and compressions do in mechanical waves. Electromagnetic waves propagate at the speed of light in a vacuum or at a slightly slower speed in various media.