1. Topic 3 – Part III The Doppler Effect
Unit 3 – Space and Exploration

2. Spectroscopes
1. Used to identify the chemical make-up of the celestial bodies
2. Used to tell us how fast a celestial body is moving toward or away from us.

3. Fire Trucks! Have you ever noticed a siren on a fire truck?
The siren sounds different as the vehicle approaches, passes and then moves away from you.
Why is this?????

4. The Doppler Effect
The siren’s change in pitch is called the Doppler Effect and is caused by the change in a sound’s wavelength.

5. Sound waves are compressed in front of the vehicle as it speeds along.
This results in shorter wave length and higher pitch
Behind the vehicle the sound waves stretch out
This results in longer wavelength and lower pitch.

6. Light! Light also travels in waves
Sooooo…..
The Doppler Effect can be used to measure the speed and direction of light-emitting objects like stars
Sound waves differ in pitch as they move, Light waves differ in color

7. How will they move?
If a star is approaching you, its wavelengths become compressed
Sooo… the dark lines in the stars spectrum shift towards the blue end.
If a star is going away from you, the wavelengths will be longer
Sooo… The dark lines in the stars spectrum shift towards the red end…. RED SHIFTED!

8. Example
Helium
Star 1
Hydrogen
Star 2