1. Prepare your scantron: Setup:
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your name.
LAST NAME FIRST, First name second
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--- (The last 4 digits of your OleMiss ID.)
Question # 1: answer A
Question # 2: answer B
Question # 3: answer E
Setup:
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2. (Joseph von Fraunhofer, 1814)
The device that resolves the colors of light:
the spectroscope
(Joseph von Fraunhofer, 1814)
• Light from telescope enters
slit (to block off stray light)
• Prism (or grating) separates
the colors
• Produces spectrum
on a screen/on a film
(Put this device in a box and
attach it to the telescope)
The spectroscope
Surprise:
The spectrum of the Sun
has black lines:
Some colors are missing!
(Fraunhofer-lines)
Spectrum: each color is a “line”

3. The spectrum of the Sun Absorption lines (“Frauenhofer-lines”),
(Color and b/w version of the same thing.) H H
Absorption lines (“Frauenhofer-lines”),
many in hydrogen wavelengths
Here: colder gas takes out a few colors
Solar atmosphere

4. the chemical composition
Types of spectra
Continuous spectrum
(thermal glow & synchrotron radiation)
Absorption spectrum
(gas illuminated from behind)
Emission spectrum
(rarified gas: fluorescence)
Each chemical element
has its own spectral lines:
A good way to tell
the chemical composition
of a star!

5. The spectra of stars – the effect of photospheric temperature

6. Questions coming …

7. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 4
How do we know that the Sun is made
mainly of hydrogen?
A Its density equals the density of hydrogen.
B Spaceships brought back a samples from the Sun.
C Its spectrum contains hydrogen lines.
D The gravity of the Sun can be explained only by hydrogen gas.
E Only burning hydrogen (and no other gases) can produce enough heat to explain why the Sun is hot.
Next question coming …

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Question 5
Which one of the following types of spectra
indicate the presence of cold gas located between a star and Earth?
A Absorption spectra.
B Emission spectra.
C Continuous spectra.
D Line spectra.
E Band spectra.

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Question 6
The spectrum of the Sun consists of
A a few bright lines only.
B dark lines over a bright continuum.
C dark bands of light with bright centers, over a bright continuum.
D a continuous bright spectrum like a rainbow.
E a few bright bands with dark centers.
Next question coming …

10. The effect of movement on spectral lines:
The Doppler effect
• Light source moves towards observer: spectral lines are shifted towards blue
• Light source moves away from observer: spectral lines are shifted towards red
• Light source moves sideways: no change

11. The spectrum of another star
The Sun H H
Polaris
Spectral lines shifted towards blue:
Polaris is approaching us
Measure shift: find radial speed
17 km/s
Why are the spectral lines shifted? -- the Doppler effect

12. Questions coming …

13. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 7
In what are spectra of other stars different from
the Sun’s?
A The same spectral lines are there in every star’s
spectra, but they may be shifted if the star is moving.
B Different spectral lines may be visible, in addition
to Doppler-shift.
C All stars have the same spectrum because they are all
made of gas.
D The spectrum is the same, except that the blue part of hotter stars’ spectra is brighter.
Next question coming …

14. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 8
What is the Doppler effect?
A Stars move on tiny circles in the sky, once a year.
B The stars appear red when they are rising or setting.
C Far-away stars appear red because the Universe is expanding.
D The spectral lines of a star are shifted towards red, if the star is moving away from us, and towards blue, if the star is approaching us.
E A fast moving star’s spectral lines are shifted towards red, independently of the direction of motion.
Next question coming …

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Question 9
A particular galaxy is moving away from us with large
speed. Which of the following happens to its spectrum?
A The spectral lines show up shifted towards red.
B The spectral lines show up shifted towards blue.
C The color of the galaxy becomes redder.
D The color of the galaxy becomes bluer.
Next question coming …

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Question 10
Which of the following happens to the sound of the whistle coming from a train approaching us at high speed?
A It becomes lower-pitched.
B It becomes higher-pitched.
C It becomes less loud.
D It becomes more loud.

17. Example: Rotational line broadening:
The details of the spectra tell a lot:
• Chemical composition: from color of lines
• Rotation: from width of lines
• Movement (towards us or away from us): from shift of lines
• Strength of magnetic field (if any): from split of lines
• Temperature, gravity, wind speed, …: from detailed
structure of lines
Example: Rotational
line broadening:
What do spectra tell us?

18. Example: a rotating galaxy
The top of the slit shows blueshift -
- stars there are moving towards us
The bottom of the slit shows redshift -
- stars there are moving away:
Example: a rotating galaxy
Example:
This galaxy rotates!

19. Questions coming …

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Question 11
How do we know that galaxies rotate?
A Their spectral lines are broad.
B The spectral lines of different parts of the galaxy show different red- and blueshift.
C The shape of a galaxy changes in a few years.
Next question coming …

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Question 12
How will the rotation of a star affect its spectrum?
A Spectral lines get blueshifted.
B Spectral lines get redshifted.
C Spectral lines broaden.
D The spectral lines are not affected, but the stars overall color changes.

22. Turn in your scantron now
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