5.6 The Doppler Effect

Motion Affects Waves: Doppler effect

the source’s motion affects the observed wavelength and frequency, but not the speed of light

Source is at rest with respect to the observer:

• Waves spread evenly in all directions, with the same wavelength 

2. Source light is moving with respect to the observer 

1. Source light is moving with respect to the observer 

1. Observer is in front of the motion: Crests are squeezed together, giving shorter wavelengths and higher frequency 

2. Observer is behind the motion: Crests are stretched out, giving longer wavelengths and lower frequency

3. Observer is to the side of the motion: Wavelengths and frequency don’t change 

Radial Velocity

The motion that causes the doppler effect

Blueshift: Wavelengths decreasing (approaching)

•  shift towards the blue end of of the spectrum

Redshift: Wavelengths increasing (Moving away

• shift towards the red end of the spectrum

• Formula:

• • Wavelength is emitted from the source of delta wavelength 

  • V is the relative speed of the observer 

    • Positive if its moving away (recessing), and negative if its approaching 

Stellar Motion shifts and light: Using the doppler effect and refraction etc help identify

1. Composition

2. Temperature 

3. And motion