1. Doppler Shift
October 19, 2009

2. Taking Care of Business (TCB)
Read textbook Units 25 and 26
No Homework next week!
Moon Observations – Monday, October 26
Need total of 9 observations, all columns filled.
Test #2 – Friday, October 16 to Monday October 19
Reserve a test time!!!!

3. What can we learn by analyzing starlight?
A star’s temperature
A star’s chemical composition
- peak wavelength of the spectral curve
- dips in the spectral curve or the lines in the absorption spectrum
A star’s motion
Moving towards us/ moving away
How fast the star is going

4. The Doppler Effect
Definition: “The change in wavelength of radiation (light) due to the relative motion between the source and the observer along the line of sight.”

5. Astronomers use the Doppler Effect to learn about the radial (along the line of sight) motions of stars, and other astronomical objects.
On a boat, in the front you can see shorter waves
Boat, in the back the waves are longer

6. Real Life Examples of Doppler Effect (Sound or Light)
Sound, NOT the volume of the sound, it’s a build of sound waves (pitch change)
Trains, airplanes, moving vehicles, police sirens, bats
Car headlights, radar gun

7. Doppler Effect
When something which is giving off light moves towards or away from you, the wavelength of the emitted light is changed or shifted
V=0

8. Doppler Effect
When something which is giving off light moves towards or away from you, the wavelength of the emitted light is changed or shifted
V=0
longer
shorter

9. Doppler Effect
When the source of light is moving away from the observer the wavelength of the emitted light will appear to increase. We call this a “redshift”.
Red because the wave length is the longest.

10. Doppler Effect
When the source of light is moving towards the observer the wavelength of the emitted light will appear to decrease. We call this a “blueshift”.
Blue, shifted towards the blue

11. Astronomy Application
V=0

12. lo = wavelength if source is not moving, 700 nm
Doppler Shifts
Redshift (to longer wavelengths): The source is moving away from the observer
Blueshift (to shorter wavelengths): The source is moving towards the observer
Dl = wavelength shift
lo = wavelength if source is not moving, 700 nm
v = velocity of source
c = speed of light
( )/700 = V/3x10^8 m/s
V= 34% C

13. The Doppler Effect causes light from a source moving away to:
be shifted to shorter wavelengths.
be shifted to longer wavelengths.
change in velocity. (In space, light will travel in a constant speed.)
Both a and c above
Both b and c above

14. Source A is moving faster than source B.
You observe two spectra (shown below) that are redshifted relative to that of a stationary source of light. Which of the following statements best describes how the sources of light that produced the two spectra were moving? BLUE RED
Spectrum A
Spectrum B
Source A is moving faster than source B.
Source B is moving faster than source A., we are told it is redshifted!
Both sources are moving with the same speed.
It is impossible to tell from looking at these spectra.

15. A bright star is moving toward Earth
A bright star is moving toward Earth. If you were to look at the spectrum of this star, what would it look like?
an absorption spectrum that is redshifted relative to an unmoving star
an emission spectrum that is redshifted relative to an unmoving star
a continuous spectrum that is blueshifted relative to an unmoving star
an absorption spectrum that is blueshifted relative to an unmoving star, blueshifted (moving towards us), absorption
a continuous spectrum that is redshifted relative to an unmoving star

16. Links to In-Class Problems
Go to astro.unl.edu
Click on “Class Action” box on right.
Light: #11, #12, #13