Radio Waves
| 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.
| 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.
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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 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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[NEXT SHORTER WAVELENGTH]
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