AnnouncementTest 2

is coming up on Mar 19.Start preparing!

This test will cover the classes from Feb 27 - Mar 14. 50 points, scantron, 1 hr.

1

Lecture-Tutorial (LT):Analyzing Spectra (pp. 69-72)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another.

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask another group.

• If you get really stuck or don’t understand what the LT is asking, ask for help.

2

AST 103Doppler Shift

Prof. Ken NagamineUNLV

3

What can we learn by analyzing starlight?

• A star’s (or any other object’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

4

The Doppler Effect• Definition: “The change in wavelength due to

the relative motion between the source and the observer along the line of sight.”

http://www.youtube.com/watch?v=Kg9F5pN5tlI5

Astronomers use the Doppler Effect to learn about the radial (along the line of sight) motions

of stars, and other astronomical objects.

6

Real Life Examples of Doppler Effect

• Doppler Radar (for weather)• Airplane radar system• Submarine radar system• Radar gun, used by police officers

7

Doppler Effect• When something that is giving off light moves

toward or away from you, the wavelength of the emitted light is changed or shifted.

V=0

redshift

blueshift

8

The Doppler Effect

• Definition: “The change in wavelength of radiation due to relative motion between the source and the observer along the line of sight.”

9

Doppler Effect• “Along the line of sight” means the Doppler

Effect happens only if the object which is emitting light is moving toward you or away from you.– An object moving “side to side” or

perpendicular, relative to your line of sight, will not experience a Doppler Effect.

10

Application to Astronomy

V=0

The shift of spectral lines can tell the motion of astronomical objects.

11

Doppler Shifts• Redshift (to longer wavelengths): The source is

moving away from the observer• Blueshift (to shorter wavelengths): The source is

moving toward the observer

Δλ = wavelength shiftλo = wavelength if source is not moving

v = velocity of sourcec = speed of light

The amount of shift is proportional to the relative velocity.12

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- Doppler shift

13

Lecture-Tutorial (LT):Doppler Shift (pp. 73-77)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another.

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask another group.

• If you get really stuck or don’t understand what the LT is asking, ask one of us for help.

14

The Doppler Effect causes light from a source moving away to:

A) be shifted to shorter wavelengths.B) be shifted to longer wavelengths.C) changes in velocity.D) Both a and c aboveE) Both b and c above

Quiz

15

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

A) Source A is moving faster than source B.B) Source B is moving faster than source A.C) Both sources are moving with the same speed.D) It is impossible to tell from looking at these spectra.

Quiz

16

A bright star is moving toward Earth. If you were to look at the spectrum of this

star, what would it look like?

A) an absorption spectrum that is redshifted relative to an unmoving starB) an emission spectrum that is redshifted relative to an unmoving starC) a continuous spectrum that is blueshifted relative to an unmoving starD) an absorption spectrum that is blueshifted relative to an unmoving starE) a continuous spectrum that is redshifted relative to an unmoving star

Quiz

17