The electromagnetic (EM) spectrum encompasses the range of possible EM wave frequencies. EM waves are made up of photons that travel through space until interacting with matter, at which point some waves are absorbed and others are reflected; though EM waves are classified as seven different forms, they are actually all manifestations of the same phenomenon. The type of EM waves emitted by an object depends on the object's temperature.
Radio waves are the lowest-frequency waves in the EM spectrum. Radio waves can be used to carry other signals to receivers that subsequently translate these signals into usable information. Many objects, both natural and man-made, emit radio waves. Anything that emits heat emits radiation across the entire spectrum, but in different amounts. Stars, planets and other cosmic bodies emit radio waves. Radio and television stations and cellphone companies all produce radio waves that carry signals to be received by the antennae in your television, radio or cellphone.
Microwaves are the second-lowest frequency waves in the EM spectrum. Whereas radio waves can be up to a mile in length, microwaves measure from a few centimeters up to a foot. Due to their higher frequency, microwaves can carry information through obstacles that interfere with radio waves such as clouds, smoke and rain. Microwaves are used for radar, landline phone calls and the transmission of computer data. Microwave remnants of the "Big Bang" radiate from all directions throughout the universe.
Infrared waves are in the lower-middle range of frequencies in the EM spectrum, between microwaves and visible light. The size of infrared waves ranges from a few millimeters down to microscopic lengths. The longer-wavelength infrared waves produce heat and include radiation emitted by fire, the sun and other heat-producing objects; shorter-wavelength infrared rays do not produce much heat and are used in remote controls and imaging technologies.
Visible Light Rays
Visible light waves are radiation that you can see with your naked eye. The different frequencies of visible light are experienced by people as the colors of the rainbow. The frequencies move from the lower wavelengths, detected as reds, up to the higher visible wavelengths, detected as violet hues. The most noticeable natural source of visible light is, of course, the sun. Objects are perceived as different colors based on which wavelengths of light an object absorbs and which it reflects.
Ultraviolet waves have even shorter wavelengths than visible light. UV waves are the cause of sunburn and can cause cancer in living organisms. High-temperature processes emit UV rays; these can be detected throughout the universe from every star in the sky. Detecting UV waves assists astronomers, for example, in learning about the structure of galaxies.
X-rays are extremely high-energy waves with wavelengths between 0.03 and 3 nanometers -- not much longer than an atom. X-rays are emitted by sources producing very high temperatures like the sun's corona, which is much hotter than the surface of the sun. Natural sources of x-rays include enormously energetic cosmic phenomena such as pulsars, supernovae and black holes. X-rays are commonly used in imaging technology to view bone structures within the body.
Gamma waves are the highest-frequency EM waves, and are emitted by only the most energetic cosmic objects such pulsars, neutron stars, supernova and black holes. Terrestrial sources include lightning, nuclear explosions and radioactive decay. Gamma wave wavelengths are measured on the subatomic level and can actually pass through the empty space within an atom. Gamma rays can destroy living cells; fortunately, the Earth's atmosphere absorbs any gamma rays that reach the planet.