An increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the red shift seen by astronomers.
- ‘The normal Doppler effect causes sound waves to get longer if the source of the sound is moving away - for example, a receding ambulance siren.’
- ‘Basically the Doppler effect is that pitch increases the closer something gets to you, and it decreases the further away it gets.’
- ‘In the astronomical setting, the Doppler effect applies to light.’
- ‘There is a familiar analogous phenomenon for sound known as the Doppler effect, which explains, for instance, why the pitch of an oncoming train changes as the train approaches and then recedes from us.’
- ‘This determination assumes the variation of the redshift is indeed a Doppler effect due to motion of the star.’