Electromagnetic waves travel through space as a combination of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Because waves do not require a medium to travel through, they can travel through a vacuum. The wave's electric and magnetic fields are self-sustaining and constantly regenerate each other as it moves. Electromagnetic waves travel at the speed of light (299,792,458 metres per second) and can be generated by a variety of sources, including oscillating charges, moving charges, and accelerating charges.