What is light?

Imagine if someone switched off the Sun. Eight minutes later, it would be pitch-dark all around us. We would see only the stars and the lights we create using electricity. We wouldn’t even be able to see the Moon. Light always comes from a source. Our most important source of light is the Sun. It is unimaginably hot and constantly sends rays of light into space. These rays travel away from the Sun in a straight line at an extremely high speed—almost 300,000 kilometers per second. Because the Sun is so far from Earth, its rays still take about eight minutes to reach us. They cover the distance to the Moon in just 1.2 seconds. When rays of light hit a solid object, they are deflected or absorbed. We can see something only when a ray of light is deflected and reaches our eyes. Our brain puts together an image from all the rays that reach the eye. We call this process “seeing.” We recognize not only the source of the rays, but also the things that deflected the light. Because light travels so incredibly fast, during a thunderstorm we always see the flash of lightning first. We hear the thunder, which is also caused by the lightning, later. Sound travels much more slowly than light. The Sun is not the only source of light. Anything that burns gives off rays of light, such as a candle or a campfire. The Moon, on the other hand, does not give off light of its own; it only reflects the Sun’s rays toward Earth. We have been using electricity for about 250 years. For example, when an electric current flows through a filament, it heats up and starts to glow. More recently, LED lamps have converted electrical energy directly into light.