Question: What is the Doppler Effect?

Edward Hughes answered on 20 Jun 2014:

The Doppler effect is what happens when you receive waves from a source that’s moving towards or away from you.

It’s easiest to explain with an example. Suppose you’re standing on the street and an ambulance goes past. As it passes you its siren goes from high-pitched a slightly lower pitch. That’s because the waves are pushed together as it approaches you (high frequency = high pitch) and stretched apart as it moves away (low frequency = low pitch).

The Doppler effect is also known as red shift / blue shift because the light from distant stars turns red or blue depending on whether they’re moving away or towards us!