Air traffic controllers use radar to direct planes near busy airports.
The moving spots of light on the radar screen show where each plane is.
Finding moving things
Airplanes get into traffic jams just as cars do—especially around a
busy airport. But people called air traffic controllers can tell where
each plane is. They use radar [(ray]{.smallcaps} dahr) to help them
direct air traffic.
Radar helps the controllers find planes that are too far away to see.
And it does this at night and in rain, fog, or snow.
A radar set sends out radio waves, much like the signals a radio station
sends. The radio waves travel in a narrow beam that sweeps around and
around in a circle. When the waves hit a flying plane, they bounce back
to the radar set. This makes spots of light appear on a special screen.
By following the moving spots of light, a controller can tell how far
away a plane is, how high it is, how fast it is flying, and which way it
is going. Then the controllers can direct air traffic, much as police
officers direct cars. They can make sure that each plane follows a safe
path to take off or to land.
Radar is used to watch other moving things, too—even the weather. When
a radar beam bounces off the drops of water in storm clouds, it creates
a weather picture. Weather forecasters can tell how big a storm is, the
direction in which it is moving, and its speed. Then people can get
ready for the storm—and airplanes can fly around it safely.
