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The nature of light has been something of a mystery to scientists since physicists first began studying it in earnest. Newton claimed that light was composed or particles, whereas his contemporary, Christiaan Huygens, was sure that light was a wave, akin to the surface of undulating water. Today, we assert the seemingly contradictory view that light is both a particle and a wave.
The study of the nature and characteristics of light is called Optics. Here are some notable characteristics of light:
As first noted by Newton, white light can be "created" by blending red, green and blue light. Other color combinations can also produce this result. The reverse process of breaking white light into its component colors is called dispersion.
Light interacts with matter in four ways: it can be emitted by matter that is hot and therefore glowing, it can absorb light, re-emitting it later, it can allow light to be transmitted, or pass through it, or it can be opaque, forcing light to reflect, or bounce off its surface.
Light delivers energy. In the particle model of light, each light particle, or photon, delivers a "quantum" of energy, depending on its frequency, or color (if visible). In the wave model of light, the energy is delivered via the wave's vibrations, or undulations. For a light source, the amount of energy delivered per unit time is its power. For a light source, the amount of energy delivered per unit area per unit time is its intensity. Intensity is also called brightness or luminosity.
While the speed of light is the specific value of 186,000 miles per second in outer space, or in air, it is a different constant value in other, denser optical (transparent) media. For example, it is "only" about 140,000 miles per second in water. Nevertheless, whatever optical medium you observe light in, the speed in that medium is a constant, and you cannot catch up to light in that medium.
The light we see is only a small fraction of all the light in the Universe: "types" of light we cannot see include radio and television waves, microwaves, infrared radiation, ultraviolet radiation, and x-rays. These invisible "types" are used both here on Earth, and received from space, for study by astronomers. Together, all "types" of light, both visible and invisible, make up the electromagnetic spectrum.
Light is used in astronomy to determine distances to, and the natures of, light emitting or reflecting objects. These objects include the Sun, the Moon, the planets, comets and other Solar System objects, nearby stars other than the Sun, our Milky Way galaxy, and other galaxies, as well as clusters of galaxies. Because most celestial bodies are too far away for us to visit, the only information we can collect about those bodies is the information that is encoded in the light coming from them.
Light cannot be grasped, because it is always on the move. It is always moving at a constant speed in outer space, or in air: 186,000 miles per second, or 300,000 kilometers per second. Light's speed is incredibly fast, but it is finite, and its value is fixed. Nothing material can reach the speed of light, let alone exceed it.
We see light, because it comes from, or bounces off matter, and then enters our eyes. Without matter, there is no light for us to see. As light passes by us, we cannot see it: only when it enters our eyes from its matter source do we see it.
Light is abundant, filling every nook and cranny of our existence. Light is what allows us to see and thereby effectively interact with our environment. But we cannot catch light and put it in a jar. It is so very close, but also untouchable.
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