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Hertzsprung-Russell Diagram−March 16• Try new format for some
clicker questions• More like test questions
• Do you understand…?• Fewer leading questions
• Public viewing sessions at MSU campus observatory.• Fri & Sat, 9-11pm, if it is
not cloudy.• Mar 18 & 19• Apr 15 & 16• May 13 & 14
• 24-inch telescope in dome• small telescopes outside
• Do you understand? Reading Hertzsprung-Russell Diagram
• Main sequence is a mass sequence• Lifetime of stars• Do you understand? HR Diagram of star
cluster
Hertzsprung-Russell (H-R) Diagram• Stars: A-Aldebaran; B-Barnard’s Star; C-
Capella; D-Rigel1. What do you need to know about stars to
answer the next 4 questions? Pick one correct ans.a. Hot-plate model of starb. Model of the solar interiorc. How to read H-R Diagramd. Spectrum of black bodye. Energy generation in the sun
2. Which is the hottest star?3. Which is the smallest star?4. Which is the biggest star?5. If stars A-D replaced the sun, would
people be able to live in Michigan?a. YNNNb. NYNNc. NNYNd. NNNYe. NNNN
O B A F G K MSpectral class
25,000 10,000 6000 3000ç Temperature (K)
Lum
inos
ity (
L sun
) è
104
1
10-4
[see Fig. 11.10]
Hertzsprung-Russell (H-R) Diagram• Stars: A-Aldebaran; B-Barnard’s Star;
C-Capella; D-Rigel1. What do you need to know about stars
to answer the next 4 questions? Pick one correct ans.a. Hot-plate model of star: L=R2T4
b. Model of the solar interior Xc. How to read H-R Diagramd. Spectrum of black body: Hotter=>bluere. Energy generation in the sun X
2. Which is the hottest star?3. Which is the smallest star?4. Which is the biggest star?5. If stars A-D replaced the sun, would
people be able to live in Michigan?a. YNNNb. NYNNc. NNYNd. NNNYe. NNNN
O B A F G K MSpectral class
25,000 10,000 6000 3000ç Temperature (K)
Lum
inos
ity (
L sun
) è
104
1
10-4
[see Fig. 11.10]
Taking a star’s temperature
Two Ways:• Compare amount
of light in two colors• Blackbody curve
• Spectroscopy
Sodium
Hydrogen
Calcium
Mercury
Neon
Wavelength è
5000o
4000o
3000o
Emitt
ed e
nerg
ype
r uni
t sur
face
are
a è
Wavelength èç Energy
[Fig. 5.10]
2
Annie Jump Cannon: Classify stars by their spectra
Very efficient: Draper catalog has 250,000 stars
Flux
à
Wavelength à
O
B
F
A
G
K
M
G
AJC 1863-1941
• Prof. Pickering’s Team in 1913, from Barbara L. Welther, 1982, Isis 73, 94.
• AJC• BA, Wellesley, 1884• Pickering’s assistant,
1896• Henry Draper
catalog of stars, 1918-1924
• Astronomer 1938
AJC
Stellar spectral types• A Temperature Sequence Type Temperature
O >30,000
B 10,000-30,000
A 7500-10,000
F 6000-7500
G 5000-6000
K 3500-5000
M <3500
in K
[see Table 11.1]
Extra-Credit for best OBAFGKM mnemonic.• 3 clicker points for entering.• 3 clicker points for 10 best answers that can be repeated in class.• Enter in Angel before Test 3.
The H-R Diagram with Sizes
25,000 10,000 5,000 3,000 Temperature
Lum
inos
ity →
106
104
102
100
10-2
10-4
The H-R Diagram with sizes
3
The H-R Diagram with schematic sizes
25,000 10,000 5,000 3,000 Temperature
Lum
inos
ity →
106
104
102
100
10-2
10-4
[Fig. 11.10]
Mass determines location on main sequence
25,000 10,000 5,000 3,000 Temperature
Lum
inos
ity →
106
104
102
100
10-2
10-4 Low mass
High mass
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