Imagine a siren on a fire truck…
· When the truck is approaching you: The siren’s sound waves are compressed, making it sound higher pitched. It’s like the truck is “pushing” the waves together.
· When the truck is moving away from you: The siren’s sound waves are stretched out, making it sound lower pitched. It’s like the truck is “pulling” the waves apart.
This is the Doppler effect: the change in pitch of a sound wave due to the relative motion between the source of the sound and the observer.
The same concept applies to light waves, with objects moving toward us appearing bluer and those moving away appearing redder.
