Light

Light is a kind of energy that travels in waves and lets us see the world. Most of the light around us comes from the Sun. Light also comes from fire, light bulbs, lightning, and even some living things like fireflies. Without light, our eyes would have nothing to work with, and there would be no colors, no shadows, and no plants.

Light travels faster than anything else in the universe. It moves at about 186,000 miles per second. At that speed, a beam of light could circle the entire Earth more than seven times in a single second. Nothing we know of travels faster.

Even though light is fast, space is huge. Light from the Sun takes about 8 minutes to reach Earth. Light from the next closest star takes more than four years. When astronomers look through big telescopes, they sometimes see light that has been traveling for billions of years. In a real way, telescopes are time machines that show the universe as it used to be.

Light behaves like a wave. Different waves have different lengths, and the length of the wave decides the color. Red light has the longest waves your eyes can see. Violet light has the shortest. All the colors mixed together look white, which is what sunlight is. A prism, or a raindrop, can split white light back into its separate colors. That is how rainbows form.

Your eyes only see a small slice of all the light that exists. Beyond red is infrared light, which you feel as heat. Beyond violet is ultraviolet light, which can give you a sunburn. Radio waves, microwaves, and X-rays are also forms of light, just with waves too long or too short for humans to see. Bees can see some ultraviolet light, and many flowers have patterns that only bees can spot.

Light is also strange. Scientists have found that light acts like a wave in some experiments and like a stream of tiny particles in others. The particles are called photons. For a long time, physicists argued about which answer was right. The answer turned out to be both. Light is a wave and a particle at the same time, a puzzle that still amazes the scientists who study it.

Plants use light to make their food through photosynthesis. Almost every living thing on Earth depends on that food chain. In a way, light is the start of nearly all life.