Electromagnetic waves consist of travelling electric and magnetic fields. Unlike water waves or sound waves, electromagnetic waves can travel and transmit energy in free space — that is, they don’t need a medium to travel. Electromagnetic waves can travel very (very) fast: 300 million metres per second, or more than 670 million miles per hour in a vacuum.
The waves in the electromagnetic spectrum are identified by their wavelength (a measure of the distance between adjacent peaks and troughs) and frequency (the number of cycles of a wave passing a point in one second). You can learn about how wavelength, frequency and energy inter-relate in this fun activity.
Electromagnetic waves occupy a continuous spectrum. At the low-frequency, long wavelength end of the scale are radio waves. At the other extreme are very high energy, high frequency gamma rays. In between are microwaves, light, and X-rays. Visible light — arguably the most important part of the electromagnetic spectrum for us humans — is a small part of the full optical spectrum which also includes infrared and ultraviolet light.
You can find out more from this introductory video, brought to you by NASA Science.
Marconi Van 