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The Electromagnetic Spectrum header 
graphic

Radio Waves

Diagram of the radio region of the electromagnetic spectrum.
Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football. Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones. Image of a portable radio.
Image of a TV set. The antennae on your television set receive the signal, in the form of electromagnetic waves, that is broadcasted from the television station. It is displayed on your television screen.

Cable companies have antennae or dishes which receive waves broadcasted from your local TV stations. The signal is then sent through a cable to your house.

Why are car antennae about the same size as TV antennae?

Cellular phones also use radio waves to transmit information. These waves are much smaller that TV and FM radio waves.

Why are antennae on cell phones smaller than antennae on your radio?

Image of a child talking on a cell phone.


How do we "see" using Radio Waves?

Objects in space, such as planets and comets, giant clouds of gas and dust, and stars and galaxies, emit light at many different wavelengths. Some of the light they emit has very large wavelengths - sometimes as long as a mile!. These long waves are in the radio region of the electromagnetic spectrum.

Because radio waves are larger than optical waves, radio telescopes work differently than telescopes that we use for visible > light (optical telescopes). Radio telescopes are dishes made out of conducting metal that reflect radio waves to a focus point. Because the wavelengths of radio light are so large, a radio telescope must be physically larger than an optical telescope to be able to make images of comparable clarity. For example, the Parkes radio telescope, which has a dish 64 meters wide, cannot give us any clearer an image than a small backyard telescope!

In order to make better and more clear (or higher resolution) radio images, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array. Together, the dishes can act as one large telescope whose size equals the total area occupied by the array.

Three radio telescopes, dishes turned towards the sky.

The Very Large Array (VLA) is one of the world's premier astronomical radio observatories. The VLA consists of 27 antennas arranged in a huge "Y" pattern up to 36 km (22 miles) across -- roughly one and a half times the size of Washington, DC. The VLA from the air, the Y pattern visible.

The VLA, located in New Mexico, is an interferometer; this means that it operates by multiplying the data from each pair of telescopes together to form interference patterns. The structure of those interference patterns, and how they change with time as the earth rotates, reflect the structure of radio sources in the sky.


What do Radio Waves show us?

The Milky Way galaxy in the radio, gas in a horizontal line.

The above image shows the Carbon Monoxide (CO) gases in our Milky Way galaxy.

Many astronomical objects emit radio waves, but that fact wasn't discovered until 1932. Since then, astronomers have developed sophisticated systems that allow them to make pictures from the radio waves emitted by astronomical objects.

Radio telescopes look toward the heavens at planets and comets, giant clouds of gas and dust, and stars and galaxies. By studying the radio waves originating from these sources, astronomers can learn about their composition, structure, and motion. Radio astronomy has the advantage that sunlight, clouds, and rain do not affect observations.

Did you know that radio astronomy observatories use diesel cars around the telescopes? The ignition of the spark plugs in gasoline-powered cars can interfere with radio observations - just like running a vacuum can interfere with your television reception!

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NASA Official: Ruth Netting
Last Updated: March 27, 2007
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