What is the
The Electromagnetic Spectrum

The electromagnetic spectrum is a vast band of energy frequencies extending from radio waves to gamma waves, from the very lowest frequencies to the highest possible frequencies.

The spectrum is arranged by the frequency of its waves, from the longest, lowest energy waves to the shortest, highest energy waves.

Our ability to tune in the more exotic electromagnetic waves has grown in recent decades. For instance, radio is part of the spectrum, and it was only in the 20th Century that humans began to be able to use any of the electromagnetic spectrum, starting with radio at the long-wave end of the spectrum.

Today, living and working in the 21st century, we make great use of the electromagnetic spectrum in all of our vocations and avocations. All of the frequencies we use for transmitting and receiving energy are part of the electromagnetic spectrum. For instance:
  • RADIO. We use the radio portion of the electromagnetic spectrum for many things, including television and radio broadcasting, telephones and other wireless communications, navigation and radar for a variety of measurements including police speed traps, and even microwave cooking ovens.

    Our AM broadcast stations transmit signals in what is referred to as the medium-wave portion of the spectrum. FM music stations use very high frequency (VHF) transmitters. Television stations use the VHF and ultra high frequency (UHF) regions of the spectrum.
    Where are AM and FM radio signals? »       What is VHF and UHF? »

  • INFRARED LIGHT. Infrared light is on the spectrum at frequencies above radio and just below the range of human vision. Infrared light is heat. Three-quarters of the radiation emitted by a light-bulb is IR. We use infrared transmitters to remotely control our TV sets. We can record infrared light on photographic film and we have equipment that can see hot bodies in deep space in the infrared light they send out.

    electromagnetic spectrum
    electromagnetic spectrum
  • VISIBLE LIGHT. Visible light, which we receive with our eyes, is along the spectrum between infrared and ultraviolet light, which we can't see. Of course, we can collect visible light with photographic film.

  • ULTRAVIOLET LIGHT. On the spectrum, ultraviolet light is above visible light. UV is dangerous to living organisms. So, it is used to sterilize medical instruments by killing bacteria and viruses. We have photographic film that can capture ultraviolet light. Ten percent of the energy radiated by our star, the Sun, is ultraviolet light.

  • X-RAYS. Farther along the spectrum are X-rays. Their invisible energy is produced when gas is heated to millions of degrees. X-ray energy is absorbed by matter it penetrates depending upon the atomic weight of that matter. Because X-rays can change a photographic emulsion just as visible light does, we use them to take pictures of the insides of people and things.

  • GAMMA RAYS. Gamma rays are beyond X-rays on the electromagnetic spectrum. Gamma rays that we find arriving at Earth from deep space are the result of violent cosmic events such as supernovas, other nuclear explosions, and radioactive decay. Earth's atmosphere shields life on the surface from gamma rays.

What are frequencies, wavelengths and the energy spectrum?

Depiction of a sine wave
sine wave
It's all about waves. A wave is a disturbance traveling through space, transferring energy from one point to the next without permanently changing space itself. Physicists have depicted a wave graphically as the passage of such a disturbance over time.   sine wave graphic »

Frequency. The rate of change in the wave is its frequency. Notice in the graphic at right how the wave undulates up and down from peaks to valleys to peaks. The time from one peak to the next peak is one cycle. A single unit of frequency is equal to one cycle per second.

Hertz. Scientists refer to a single cycle as one Hertz, which commemorates 19th century German physicist Heinrich Hertz whose discovery of electromagnetic waves led to the development of radio.

Sine waves have frequency. A sine wave is a deviating waveform expressed graphically as a sine curve. The succession of green curves undulating in the blue graphic above right depict a sine wave. The frequency of a sine wave is the number of times it oscillates up and down per second.

Spectrum. Physicists see energy undulating at various rates. They describe the complete range of possible cycle times as a spectrum of energy.

Electromagnetic. Magnetism is produced by an electric charge in motion. Electromagnetism is the physics of electricity and magnetism. Charges of electrical energy in motion are said to be electromagnetic.

Electromagnetic spectrum. Thus, the complete range of potential energy cycles is the electromagnetic spectrum.

Deep Space Sensors

Learn more:
  • Hubble Space Telescope sees visible light »
  • Chandra X-Ray Observatory detects x-rays »
  • Spitzer Space Telescope sees infrared light »
  • Compton Gama Ray Observatory detected gamma rays »
  • Only recently have we been able to make radio receivers and sensors, covering the UHF to gamma ray part of the electromagnetic spectrum, small enough and sensitive enough to send to space as part of orbiting telescopes.
    more about spectrometers »

    NASA developed its set of four Great Observatories In Space to extend mankind's knowledge of astronomy and life itself. Each observatory has had its own specialized instruments to gather data from its assigned part of the electromagnetic spectrum.

    More About Radio

    We use a small segment of the electromagnetic spectrum to transmit the programmed energy that we refer to as RADIO.

    Suppose you are driving and listening to a talk show coming from a station at 870 on the car radio's AM dial. The radio is tuned to a specific sine wave with a frequency of 870,000 Hertz (cycles per second).

    You tire of talk and decide to switch to music on a station at 103.9 on the radio's FM dial. You tune to a sine wave being transmitted at 103,900,000 Hertz (cycles per second).

    In the United States, popular radio signals are AM transmitted in the frequency range of 530-1700 kHz and FM in the frequency range of 88-108 MHz.

    Some Specific Frequencies
    atomic clocks60 kHz
    0.500-2000 MHz
    AM radio0.535-1.7 MHz
    shortwave radio3-30 MHz
    WWV time2.5 MHz
    5.0 MHz
    10 MHz
    15 MHz
    20.0 MHz
    CHU time3.330 MHz
    7.335 MHz
    14.670 MHz
    CB radio27 MHz
    baby monitor49 MHz
    surveillance tracking radios50-1300 MHz
    cordless phones49 MHz
    900 MHz
    2400 MHz
    TV channel 2-654-88 MHz
    radio-control planes72 MHz
    radio-control cars75 MHz
    FM radio88-108 MHz
    TV channel 7-13174-220 MHz
    wildlife tracking collars215 Mhz
    cell phone800 MHz
    2400 MHz
    video transmitter902 MHz
    2400 MHz
    5800 MHz
    air traffic control radar960 MHz
    1215 MHz
    GPS1227 MHz
    1575 MHz
    deep space radio2300 MHz
    radar gun x-band10.525 GHz
    1 cycle per second = 1 hertz (Hz)
    1,000 hertz = 1 kilohertz (kHz)
    1,000 kilohertz = 1 megahertz (MHz) = 1 million hertz
    1,000 megahertz = 1 million kilohertz = 1 gigahertz (GHz) = 1 billion hertz

    Bands of Frequencies
    VLFVery Low Frequency3-30 kHz
    LFLow Frequency30-300 kHz
    MFMedium Frequency300-3000kHz
    HFHigh Frequency3-30 MHz
    VHFVery High Frequency30-300 MHz
    UHFUltra High Frequency300-3000 MHz
    SHFSuper High Frequency3-30 GHz
    EHFExtremely High Frequency30-300 GHz

    Converting Frequency and Wavelength
    Frequency in megahertz X wavelength in meters = 300
    Frequency in kilohertz X wavelength in meters = 300,000

    Frequency and Wavelength of Energy in the Electromagnetic Spectrum
    EnergyFrequency in hertzWavelength in meters
    gamma-rays1020-1024<10-12 m
    x-rays1017-10201 nm-1 pm
    ultraviolet1015-1017400 nm-1 nm
    visible4-7.5x1014750 nm-400 nm
    near-infrared1x1014-4x10142.5 um-750 nm
    infrared1013-101425 um-2.5 um
    microwaves3x1011-10131 mm-25 um
    radio waves<3x1011>1 mm

    Learn more:

  • How telescopes work in different wavelengths »
  • How the radio spectrum works »
  • Conversion from U.S. customary to metric units »
  • Understanding space technology — spectrometers »
  • 400th anniversary of the telescope »

  • Space telescopes: Spitzer Chandra Hubble Compton Telescopes Deep Space Great Observatories
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