What are doppler shifts?

A doppler shift is when something changes because it’s moving toward or away from you, like a sound getting higher or lower depending on whether it's coming closer or going farther.

Imagine you're sitting on the sidewalk, and a friend is riding a bike with a loud beep attached to the back. When your friend rides toward you, the beep sounds higher, almost like it’s shouting at you. But when they ride away, the beep sounds lower, like it’s whispering goodbye.

That’s exactly what happens with doppler shifts! If something is moving toward you, its waves (like sound or light) get squished together and become more frequent, that makes them seem higher in pitch. If it moves away from you, the waves stretch out and become less frequent, making them seem lower.

Think of a bike bell as a sound wave. When your friend is coming closer, each ring of the bell happens faster, so you hear it more quickly, like a fast beat. When they go away, each ring takes longer to reach you, making it feel slower and deeper.

It’s like how a fire truck siren sounds higher when it's zooming toward you, then lower as it passes by and drives off. That’s the doppler shift in action!