1. The Doppler Shift Brenda goes on another long voyage.x

2. Ali sends Brenda a message every year
Ali sends Brenda a message every year. How many messages does she receive on the way out, back? t t’ x

3. The frequency is greater on the way back when the ship is moving toward the signals. This is similar to the Doppler shift for sound. t t’ x

4. Brenda also sends Ali messages every year
Brenda also sends Ali messages every year. How many will he receive compared to Brenda? A) the same number B) fewer C) more x

5. She sends fewer because fewer years have passed for her and so Ali receives fewer.t t’ x

6. Reality Check #5: Physicists know that the universe is expanding because the frequency of light from galaxies is Doppler shifted.

7. The galaxies are moving so fast, that astronomers must use the formula for the relativistic Doppler shift, fo = fe (1-v/c)/(1+v/c)

8. This animation shows how things would look to an observer moving to the right. It shows the colour changes due to the relativistic Doppler shift and the distortion of space.