By Joan Whetzel
The electromagnetic spectrum, a scale that measures all types of electromagnetic radiation, was produced to rank the different types of radiation based according to the amount of energy they put out. The scale includes not only the small portion of the electromagnetic radiation that affects us here on earth, but others that are deflected by our atmosphere.
The Electromagnetic Spectrum
The electromagnetic spectrum includes all frequencies electromagnetic (EM) radiation. These energy waves contain both electrical and magnetic fields that can broadcast their way through the vacuum of space, oscillating perpendicular to each other. This EM radiation can be thought of as a flow of photons that trek through space in oscillating configuration at the speed of light. The only difference between the different EM radiation types is the quantity of energy each photon creates.
The EM spectrum chart identifies each form of EM radiation by its wave frequency, listing the frequencies in increasing order and the wavelengths decreasing in order. The portion of the spectrum affecting earth, listed in order, includes radio waves (with the lowest frequency and greatest wavelength), microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma rays (with the highest frequency and shortest wavelength). The frequency is measured by counting the number of waves occurring in one second. Wavelength is determined by measuring the distance between the wave's peaks or crests.
Electromagnetic Frequencies (EMF)
Humans can see the electromagnetic frequencies (EMF) of a light within a very small range known as visible light. The wavelength range of the visible light spectrum falls between 4,000 and 7,000 angstroms (1 angstrom = 10-10 meters, or 0.00000001 meter). Radio wavelengths, for example, have a wavelength that ranges anywhere from more than a few feet to several miles apart.
Comparing the EM spectrum to octaves in music, the visible spectrum would only occupy a portion of an octave on a piano keyboard. The entire EM spectrum currently known to science, on the other hand, would be about 27 octaves long, compared to a piano keyboard, which only has 7 octaves. The list below illustrates the wavelengths and frequencies for Earth's EM spectrum.
EM Radiation Wavelength Wavelength Frequency
Type in Angstroms in centimeters in Hertz (Hz)
Radio > 108 >10 < 3 x 109
Microwave 109 to 106 10 to 0.01 3 to 3 x 1012
Infrared 106 to 7000 0.01 to 7 x 10-5 3 x 109 to 3 x 1014
Visible Light 7000 - 4000 7 x 10-5 - 4 x 10-5 3 x 1012 - 4.3 x 1014
Ultraviolet 4000 - 10 4 x 10-5 - 10-7 7.5 x 1014 - 3 x 1017
X-Rays 10 - 0.1 10-7 - 10-9 3 x 1017 - 3 x 1019
Gamma Rays < 0.1 < 10-9 > 3 x 1019
Earth's EM Radiation
· Radio waves, the type used by radio stations, are emitted by stars and gases in space.
· Microwaves, typically used for nuking popcorn in a fraction of the time it takes to cook stovetop, are used by astronomers worldwide to determine the construction and configuration of our own galaxy as well as those nearest the Milky Way.
· Infrared is emitted by our skin in a form that can be picked up by infrared cameras and night vision goggles. In space, IR light helps astronomers chart the space dust between stars.
· Visible light, the light we can see with the unaided eye, is produced by everything from the dimmest fireflies to the most brilliant stars. The visible spectrum is usually divided into its individual colors: Red, Orange, Yellow, Green, Blue and Violet.
· Ultraviolet (UV), is the form of radiation produced by our sun and other "hot" matter in space. EM radiation at this level is strong enough to burn our skin in large enough doses.
· X-Rays, used by doctors and hospitals to take pictures of our bones and teeth, are hot gases produced naturally here on Earth, by the sun and elsewhere throughout the Universe. It is not harmful in small doses, and humans are exposed to it naturally every day. In large doses, however, x-rays are harmful, even fatal.
· Gamma rays, is a form of energy produced naturally here on Earth and in space, and also occurs in manmade items (e.g. nuclear power plants). Particle accelerators occasionally produce gamma rays, but the biggest producer of gamma rays is the Universe itself.
NASA Goddard Space Flight Center. Electromagnetic Spectrum. Downloaded 1/9/2012. http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
Pickover, Clifford A. The Physics Book. New York: Sterling Publishing, 2011.
The University of Tennessee. Regions of the Electromagnetic Spectrum. Downloaded 2/10/2012. http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html