1. Prepare your scantron:
Use
a pencil,
not a pen!
Fill in your name and fill the bubbles under
your name.
LAST NAME FIRST, First name second
Put your 4-digit code instead of “IDENTIFICATION NUMBER”.
--- (The last 4 digits of your OleMiss ID.)
Question # 1: answer A
Question # 2: answer C
Question # 3: answer B
Setup:
Recall reading assignment:
Chapter 5 (Light and matter): pp. 137 – 164
Please take a moment to mute your cell phone!

2. Photons Einstein’s  light comes in chunks (photons)
discovery:  each photon has E=1240/l energy
Red l = 720 nm, E = 1.7 eV
Blue l = 420 nm, E = 3 eV
UV l = 100 nm, E = 12 eV
X-ray l = 1 nm, E = 1200 eV
in electron-volts (eV) in nm’s
Enough to destroy most atoms
Destroys everything if strong

3. Phases The phases of matter  Solid  Liquid (only under pressure
– rarely in astronomy)
 Gas
Phases
Distinction looses sense
under great pressure
(inside stars or planets)
 that matter is “mush”
Hot matter:
T > 1, ,000 K falls apart into atoms (gas or “mush”)
T > 2, ,000 K atoms are ionized (plasma)
Ultraviolet radiation will also ionize matter

4. Cosmic rays From Deep Space (??) The Solar Wind protons, electrons
Earth’s
atmosphere and magnetic field
absorb them
(dangerous for astronauts)
very energetic protons & nuclei
Break up into showers
of many less energetic particles
in the atmosphere.
(always present: causes mutations)

5. Questions coming …

6. 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
What is ionization?
A Molecules fall apart into atoms due to heat.
Glowing gas is formed.
B Nuclear processes in stars produce dangerous radiation.
C Atomic nuclei fall apart into neutrons and protons.
A neutron star results.
D Atoms lose (some of) their electrons due to heat or UV
radiation. The substance becomes plasma.
Next question coming …

7. (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”

8. 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

9. 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!

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

11. Questions coming …

12. 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 5
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 …

13. sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21
Question 6
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.

14. sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22
Question 7
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 …