EXPLORE: Redshift & Blueshift (BrainPop)

An analogy to redshift & blueshift is the noise a siren makes as it passes by you. You may have noticed that the siren on an ambulance has a lower pitch  after it passes you. The sound waves shift towards a lower pitch when the ambulance speeds away from you because the wavelength is getting longer. The opposite happens when an ambulance is speeding towards you: the pitch gets higher because the sound waves are closer together (in other words, they have a shorter wavelength). The Doppler Effect occurs when the wavelength of waves emanating from a moving source appears to be longer or shorter, depending on whether the object is moving towards or away from the observer. 

Though redshift and blueshift involve light waves instead of sound waves, a similar principle operates in both situations. Explore the next interactivity in the course about the Doppler Effect, a change in wavelength caused by the motion of the source. As an object moves away from you, the wavelength increases (redshift). As an object moves towards you, the wavelength decreases (blueshift).