Fun Fact: Both natural and artificial light starts inside atoms, tiny pieces of matter much too small for anyone to see. Changes inside atoms give off light.
How Light Travels
Light travels at very high speed. It travels through space faster than anything we know of. You can tell that light travels faster than sound when you see lightning. You’ll notice that you usually have to wait a few seconds after the lightning bolt to hear thunder. Thunder is the sound that lightning makes.
The speed of light through empty space is about 300,000 kilometers per second. Astronomers talk about vast distances in space as light-years.
Fun Fact: A light-year is how far a beam of light can travel in one year, or about 9.5 trillion kilometers.
Sometimes light seems to travel as waves. You can see waves ripple through water. You can see waves travel back and forth in a rope that you shake up and down. Most waves must travel through something, but light waves can travel through empty space.
READ ALSO: Electricity: Its Impact on The World
Fun Fact: Sometimes light seems to travel as little bundles of energy. The bundles are called photons.
Colors of Light
Fun Fact: Sunlight is made up of every color in the rainbow
When sunlight is spread out into all its colors, it makes what scientists call a spectrum. A rainbow is a spectrum. In a spectrum, each color flows into the color next to it.
You can think of light rays as strands of color. Each colored strand, or ray, has energy. The color of a ray of light depends on how much energy it has. Violet has high energy. Red has lower energy. The colors between violet and red make up the light we can see. This light is called visible light.
Beyond violet are ultraviolet light rays that you cannot see. Ultraviolet rays from the Sun and from artificial light can cause sunburn. Infrared light rays are beyond red. You cannot see infrared rays, but you can feel them as heat.
Why Is the Sky Blue?
The sky looks blue because air scatters the different rays of colored light in sunlight. When light rays scatter, they go off in different directions. Air scatters blue light much more than any of the other colors in sunlight. Most colors travel directly from the Sun to the ground, but blue gets scattered all over, turning the whole sky blue.
At sunset, however, the sky sometimes looks red. At sunset, when the Sun is at the horizon, light rays have to travel longer distances and through more air to reach you. This extra air scatters blue light so much that the blue light gets absorbed or bounced into space before it gets to you. Most of the light left to see is red.
Hot and Cool Light
Light that comes from heat is called incandescent light. The Sun is blazing hot. Sunlight is incandescent light. An ordinary light bulb gets so hot that it could burn you. An ordinary light bulb gives off incandescent light.
Light that comes from cool sources is called luminescent light. Some kinds of chemicals and electric energy give off light without giving off heat. Chemicals in a fluorescent tube give off luminescent light when electricity goes through the tube. You can touch a fluorescent light bulb without getting burned.
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