Science glossary film: Echo

The reflection of a sound wave back to a listener, so it is heard again after the original noise. Though the word usually refers to sound, any form of wave energy can create echoes. Astronomers, for example, observe light echoes, where light from a very energetic event is reflected off clouds of dust and gas.

Though the word usually refers to sound, any form of wave energy can create echoes. Astronomers, for example, observe light echoes, where light from a very energetic event is reflected off clouds of dust and gas.