Electromagnetic waves can travel and transport energy without a medium through which it may travel. This contrasts with mechanical waves, such as sound waves, which cannot travel through a vacuum. If electromagnetic radiation could not travel through a vacuum, the sun’s rays would not light the Earth.
Electromagnetic waves occur in a wide variety of wavelengths and frequencies. The wavelength of an electromagnetic wave affects its properties, such as whether it is visible or harmful. Scientists refer to the variation in the wavelengths of different types of waves as the electromagnetic spectrum. Those waves with the shortest wavelengths are called gamma rays, while X-rays and ultraviolet rays have slightly longer wavelengths. These waves are invisible to the naked eye, and the short waves are harmful to living cells. Visible light has wavelengths slightly longer than those of ultraviolet rays, and such waves enable humans and other animals to see. Infrared wavelengths are even longer than visible rays. Even longer than infrared waves are microwaves and radio waves. All of these waves can be manipulated so that they contain information. Because this information does not require a medium to travel through, messages can be sent through the vast distances of space. This allows scientists to communicate with space stations and satellites, as well as potentially communicating with other life forms, if they are discovered.