Science glossary film: Doppler shift

A change in the observed frequency of a wave when it is emitted from a moving object and observed from a stationary point, or vice versa. The effect is most easily noticed with sound waves. For example, a train moves fast enough to create a change in frequency that we can clearly hear as a change in pitch. But it works with any wave, and by measuring the Doppler shift of light from distant stars and galaxies we can infer how fast they are moving and in which direction.

The effect is most easily noticed with sound waves. For example, a train moves fast enough to create a change in frequency that we can clearly hear as a change in pitch. But it works with any wave, and by measuring the Doppler shift of light from distant stars and galaxies we can infer how fast they are moving and in which direction.