Astronomy Fundamentals

Matter and Energy

What is light?

Light is a kind of energy. It travels as waves and is carried as particles called photons. Generally speaking, light is electromagnetic radiation. (Radiation carried by massive particles, however, such as alpha rays and beta rays, is not light.) What is interesting about light is that it can be treated as both a stream of particles and as a wave of radiation. The double nature of light—known as “wave-particle duality”—is a cornerstone of the branch of physics called quantum mechanics.


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