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Radio Waves
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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.
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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?
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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?
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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.
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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.
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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, 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.
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What do Radio Waves show us?
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.
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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.
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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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RETURN TO THE ELECTROMAGNETIC SPECTRUM
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