Light cooks your food.  Light changes your television station.  Light carries music to your radio.  Light is much more than what your eyes can see.  In fact, light is any kind of energy that moves in waves at the speed of light -- about 186,000 miles each second.  Let's look at the light that is beneath the colors your eyes can see.

Wait, you mean a prism bends the light I can't see too?

When you step out into the sun, can you feel the heat?  William Herschel did in 1800.  He used a piece of glass called a prism to divide white light into all the colors of the rainbow.  Slowly he passed a thermometer through all the colors, beginning with violet, the coolest, and ending with red, the warmest.  Then he moved it just past red and found it was even hotter there.  The heat came from infrared light.  Infrared light can be felt as heat, and it has wavelengths about as wide as one of your hairs.

Infrared is truly hot stuff; anything warm -- like your body-- gives off this kind of light.  It can move through walls, clouds and even space to let people "see" in the dark.  At home, your TV remote shoots this light across your living room to change the channel.  At the grocery store, the cashier uses this light to scan the things you buy, so you know how much to pay.  Police and search teams use this kind of light to find people who may be lost in the cold by sensing their warm bodies.  People use it to "see" things far away in space since this kind of light can go great lengths and even move through space dust.

Some light waves are as long as a football field.  They carry broadcasts a long way.  Tune your TV or radio to a station, and it will pick up this type of light.  Once it catches these waves, it changes them to pictures your eye can see and sounds your ears can hear.  Outer space is full of these kinds of waves; astronomers have built big telescopes to gather the waves and learn about space.  This kind of light, called a radio wave, is light with a wavelength between 1 millimeter and 30,000 meters.

No, you jump in first.

Heinrich Hertz discovered radio waves in the 1880's; he made a loop out of copper that had a small space between two pieces of wire.  He connected the wires to electricity and saw a spark jump across the open space. This is like when you drag your feet along the floor during the winter, and then touch your friend's arm; you feel a shock.  He also built a piece of equipment that would detect these waves by forming a circle out of copper wire and leaving a space between the ends.  Whenever he made a spark on his machine, an electric charge jumped across the space on the detector too because the radio waves moved across the room.  This is like when you toss a rock in a pond; even if you do not see the rock go in, you know it did just by seeing the waves move across the pond.

One kind of radio wave includes the kind of light that cooks your frozen dinner.  The waves move inside the food and give energy to the water inside the food.  This makes the food heat up and cook!  This same kind of light carries your cell phone calls across the country.  They can go so far because they can move through rain, snow, clouds and smoke.  Radars use this same kind of light to bounce waves off of things, just like a ball, allowing ships and airplanes to "see" in the dark.  This form of light, called microwaves, cooks your food and has wavelengths between 3 millimeters and 30 centimeters, about as wide as a ball.

OK, who made popcorn and didn't close the door?

When most people think of microwaves, they think of food.  In fact, the birth of this kind of oven was an accident.  In 1946, after the second World War, an American scientist named Percy Spencer was making microwaves at his company.  He was standing too close to the equipment that made the waves, and later he noticed a candy bar had melted in his pocket.  This was very strange since he had not felt any heat.  He thought about these waves, what they might be able to do, and 10 years later his microwave oven was born.

From hair-thin infrared to football-field-long radio waves, our world would not be the same without light.  We need light to call our friends and cook our food.  We need light to change TV channels.  We need light to know how much a pack of gum costs at the store.  A lot of light -- powerful light -- lies beneath what we can see


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