Name __________________________ Date _____________ Block ____
E.2: Stellar Radiation and Stellar Types
E.2.1- State that fusion is the main energy source of stars
 Students should know that the basic process is one in which hydrogen is converted into helium. They
do not need to know about the fusion of elements with higher proton numbers.
E.2.2 - Explain that, in a stable star (for example, our Sun), there is an equilibrium between radiation
pressure and gravitational pressure.
“H” is Fuel
 How does our sun work?
 Fusion of hydrogen into _____________ that provides the energy, for our sun
 Happens on the inside of the sun (Yes, there are different layers)
 Produces _____________ that leave the sun and travel to Earth
 The proton-proton chain
 This is the same reaction discussed in Topic
7. Each complete chain reaction produces
__________________.
 Remember you need 4 H to end up with one
He
 See simplified equation:
Star Stability
 Gravity pulls inward
 So much the sun should collapse.
 Nuclear explosions push ______________
 These two have to balance out to be at pressure ________________
 Ex. Balloon.
 Rubber is like gravity
 Air is like the ________________
 If the temp changes the inside pressure will change and won’t be stable
E.2.3 - Define the luminosity of a star.
E.2.4 - Define apparent brightness and state how it is measured.
Luminosity
 _________________ measurements give us information about the temperature, size and chemical
composition of a star.
 Luminosity(L) is the total amount of ____________ emitted by the star per second.
 Unit is watt (same as power)
 Depends on the ________________
 Ex. Two stars have same temp, the bigger one will give out more energy
 Sun’s luminosity of 3.839 x 1026W
Apparent brightness(b)
 Some stars appear brighter than others.
 Brightness depends on:
1
a. How much energy is radiated (_______________)
b. How ________________ away it is located
 Apparent brightness(b) is the amount of energy per _______________received per unit area.
 Unit is W/m2
 b=
 d is distant to the star
E.2.5 - Apply the Stefan–Boltzmann law to compare the
luminosities of different stars.
E.2.6 - State Wien’s (displacement) law and apply it to
explain the connection between the color and
temperature of stars.
Black Body Radiation
 Black bodies absorb all ________________ of light and
reflect none. It also is a perfect emitter of radiation.
 If temp is increased the energy available is increased.
 Means the ________________ can gain more
energy and move into higher energy levels
 Means more photons released, and their average energy is ____________________.
 E = hf, Higher energy means higher frequency/shorter wavelength
Stefan-Boltzmann
 Each peek represents the__________________(apparent brightness) of radiation at different wavelengths.
 Total intensity is the area under the curve.
 Power per unit area =
 σ = 5.6 x 10-8 W/m2K4 (Stefan-Boltzmann constant)
 If a star has a surface area A and temperature T then the total power emitted (luminosity), L is given by:
 L=
Wien Displacement Law
 As the temperature increases, the peak wavelength is _________________
 Relationship between peak wavelength and temp is Wien displacement law:
 λmax = (2.90 x 10-3km) / T
Example
 The maximum in the black body spectrum of the light emitted from the sun is at 480 nm. Given that the
Sun’s radius is 7.0 x 108m, calculate the temperature of the sun, the power emitted per square meter, and the
luminosity.
 Answer: 6000K, 7.3 x 107 W/m2, 4.5 x 1026 W
2
E.2.7 - Explain how atomic spectra may be used to deduce chemical and physical data for stars.
Students must have a qualitative appreciation of the Doppler effect as applied to light, including the
terms red-shift and blue-shift.
E.2.8 - Describe the overall classification system of spectral classes.
Students need to refer only to the principal spectra classes (OBAFGKM).
Stellar Spectra
 Remember: Electrons only exist in certain energy levels
 When excited only produce specific wavelengths. (Emission Spectrum)
 When white light passes through same gas these wavelengths are
absorbed. (Absorption spectrum)
 Stars emit a continuous spectrum of EM
 Peak intensity depends on the temp.
 As this EM pass through the outer layer of the star, some is absorbed.
 The absorption spectrum of a star tells us what elements are present
because of the missing lines.
Stellar Spectra
 The absorption spectra also helps us to calculate the temperature of the gas.
 Hot gas
 Most electrons are already in higher energy levels
 Meaning they can’t make the biggest jump
 See “Energy Levels” diagram
 Means the higher energy photons will not be absorbed.
 Means a weak absorption line
 Which can let us find the temp
E.2.8 - Describe the overall classification system of spectral classes.
Students need to refer only to the principal spectra classes (OBAFGKM).
 Spectral Classification of Stars
 The spectrum of a star is related to it’s temp and chemical composition.
 Also the color. The peak points to it’s color
 Oh Be A Fine Girl Kiss Me
Doppler Shift
 As objects move, the wave lengths they produce is either pushed together or spread apart.
 Called doppler effect.
 Applies to all waves including light from stars.
 Red shift – longer λ – star moving away
 Blue shift – shorter λ – star moving closer
Class
O
B
A
F
G
K
M
Temperature
30k - 60k
10k - 30k
7.5k - 10k
6k - 7.5k
5k - 6k
3.5k - 5k
2k - 3k
Color
Blue
Blue-White
White
Yellow-White
Yellow
Orange
Red
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Hamper Practice Exercises for topics E2
4
E2 Stellar Radiation and Stellar Types
http://www.youtube.com/watch?v=ugorpmBkPE&list=PL7FD7F1082F45C268&index=3&safety_mode=true&persi
st_safety_mode=1
http://www.youtube.com/watch?v=jltK_KaVGs&list=PL7FD7F1082F45C268&safety_mode=true&persis
t_safety_mode=1
http://www.youtube.com/watch?v=VSd7A4rswbg&list=PL7FD7F1082F45C268&safety_
mode=true&persist_safety_mode=1






E.2.1 State that fusion is the main energy source of stars.
http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html

The fusion process in a young star (made mainly of Hydrogen)
is. In the fusion process, when the 4 H nuclei are converted into a He nucleus a small
amount of mass is lost as energy.
Eg/ Mass of 4 H nuclei = 6.693 x 10-27kg
Mass of 1 He nuclei = 6.645 x 10-27kg.
 What is the difference in their masses?
The mass is released as energy. The energy is given by E = mc 2.For each fusion reaction the energy
released is what? This seems like a small amount of energy but now work out the energy released by 1kg of
hydrogen atoms undergoing fusion. (Hint: use percentages)
 This is ~ burning 2 x 107kg of coal.
If the luminosity (power output) of the sun is 3.9 x 10 26W, work out how much Hydrogen the sun 'burns'
each second, and how much the equivalent in coal would be.
If the mass of the Sun is 2 x 1030kg, how many years can the sun burn for?
What factors affect the lifetime of a star?
E.2.2 Explain that, in a stable star (for example, our Sun),
there is an equilibrium between radiation pressure and
gravitational pressure.
What is the value lf the equalized pressure and radiation of our
sun?
E.2.3 Define the luminosity of a star.
E.2.4 Define apparent brightness and state how it
is measured.
http://physics.uoregon.edu/~soper/Light/luminosity.ht
ml
5
1. What two factors affect how bright a star appears in our night sky?
2. What is the formula for luminosity?
3. What is apparent magnitude? What is absolute magnitude? How are they “scaled”?
A Past IB Paper Question
The distance of Sirius A from the Sun, calculated from its parallax is 8.7 light years. One light year equals 9.46
x 1015m.
a) Explain the term parallax by sketching and labelling a suitable diagram.
b) If the distance from the Earth to the Sun is 1.5 x 1011m, calculate the parallax of Sirius A.
c) Explain what is meant by the luminosity of a star.
d) The luminosity of Sirius A is 8.17 x 1027W. Calculate the brightness of Sirius A as measured by an observer
on Earth.
E.2.5 Apply the Stefan-Boltzmann law to compare the luminosities of different stars.
E.2.6 State Wien’s (displacement) law and apply it to explain the connection between
the color and temperature of stars.
http://hyperphysics.phy-astr.gsu.edu/hbase/wien.html#c1
-Pg 756-757 Example 1 & 2 (Giancoli)
-Do pg 782 #5
1. Why do we call some stars red, some blue and others white?
2. How do we know what temperature a star is to be able to place it in the right place on the
HR Diagram.
E.2.7 Explain how atomic spectra may be used to deduce chemical and physical data
for stars.
E.2.8 Describe the overall classification system of spectral classes.
http://en.wikipedia.org/wiki/Stellar_classification
http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html
1. Explain how atomic spectra may be used to deduce chemical and physical data for
stars.
2. What is the doppler effect?
3. What is the difference between a red shift and blue shift?
4. Describe the overall classification system of spectral classes.
5. What is the classification of stars based on?
E.2.9 Describe the different types of stars? Students need to refer only to single and
binary stars, Cepheids, red giants, red supergiants and white dwarts. Knowledge of
different types of Cepheids is not required.
E.2.10 Discuss the characteristics of spectroscopic and eclipsing binary stars.
E.2.11 Identify the general regions of star types on a Hertzsprung-Russell(HR)
diagrams.
Plot an HR (Absolute Magnitude versus temperature) diagram for the local stars
Answer the questions:
2a Do you see any patterns in the distribution of points on Plot B?
2b Why are the values of m and M different for the same stars? (Absolute magnitude (M) is a
brightness quantity corrected for distance from the Earth. It is the apparent magnitude (m) a star
would have if it were 32.6 light-years from the Earth.)
2c How many stars are more luminous than the sun and how many are less luminous in the local
star group?
2d
Is this a true statement? “As the intrinsic brightness increases, so does the temperature.”
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Star
Sun
AlphaCentaruiC
AlphaCentaruiA
AlphaCentaruiB
Barnard'sStar
Wolf359
BD+36 ｺ 2147
Luyten726-8A
Luyten726-8B
SiriusA
SiriusB
Ross154
Ross248
epsilonEridani
Ross128
61CygnusA
EIndi
BD+43?44A
BD+43?44B
Luyten789-6A
Luyten789-6B
ProcyonA
ProcyonB
BD+59?1915A
BD+59?1915B
Apparent
Temperature
Absolute
Magnitude
(K)
magnitude
-26.8
4.8
5770
11
15.8
2600
0
4.4
5800
1.4
5.8
4000
9.5
13.2
2600
13.5
16.8
2400
7.5
10.5
2700
12.6
15.4
2500
13
15.8
2400
-1.4
1.4
9500
8.4
8.4
28000
10.4
13.3
2650
12.3
14.7
2500
3.7
6.1
4500
11.1
13.5
2600
5.2
7.5
4000
4.7
7
4000
8.1
10.3
2950
11.1
13.2
2700
12.3
14.9
2500
12.3
15.9
2200
0.4
2.7
6500
10.7
13
7000
8.9
11.1
2650
9.7
11.9
2600
7