1. ASTR 1200 Announcements Exam #1 in class, next Tuesday, October 7
Have posted review sheet and sample exam
Help room: Mondays 3-5,Duane G2B90
Review Lecture on Thursday
Josh review/help session time?
Solutions to Problem Sets posted tomorrow
Website

2. Planetarium
We met at the planetarium and spent half the time with a show.
In particular, we “flew” from Earth to Prox Cen and back, watching the parallax of the nearby stars.
We also “flew” to Orion’s Sword and visited a star-forming region.

3. Electromagnetic Spectrum
Wavelength increases to the right
Frequency and energy increase to the left

4. Stars Come in Different Colors

5. Stellar Temperature Stars come in different sizes and temperatures.
Can the two be linked?

6. Stellar Classification
Full range of surface temperatures from 2000 to 40,000K
Spectral Classification is Based on Surface Temperature
Hottest
O B A F G K M
Coolest {
Girl }
Oh Be A Fine
Kiss Me
Guy
Each Letter has ten subdivisions from 0 to 9
0 is hottest, 9 is coolest

7. The Spectral Types O Stars of Orion's Belt >30,000 K
Lines of ionized helium, weak hydrogen lines
<97 nm (ultraviolet)* B
Rigel
30,000 K-10,000 K
Lines of neutral helium, moderate hydrogen lines
nm (ultraviolet)* A
Sirius
10,000 K-7,500 K
Very strong hydrogen lines
nm (violet)* F
Polaris
7,500 K-6,000 K
Moderate hydrogen lines, moderate lines of ionized calcium
nm (blue)* G
Sun, Alpha Centauri A
6,000 K-5,000 K
Weak hydrogen lines, strong lines of ionized calcium
nm (yellow) K
Arcturus
5,000 K-3,500 K
Lines of neutral and singly ionized metals, some molecules
nm (red) M
Betelgeuse, Proxima Centauri
<3,500 K
Molecular lines strong
>830 nm (infrared)
*All stars above 6,000 K look more or less white to the human eye because they emit plenty of radiation at all visible wavelengths.

8. Stellar Classification (2)
Sun G2
a Cen G2 + K5
Sirius A1
Antares M1
Rigel B8
O5 40,000K
B5 15,500
A5 8500
F5 6580
G5 5520
K5 4130
M5 2800
Letters are odd due to confusion in sorting out temperature scale
between 1900 and 1920

9. Stellar Classification
Full range of surface temperatures from 2000 to 40,000K
Spectral Classification is Based on Surface Temperature
Hottest
O B A F G K M
Coolest {
Girl }
Oh Be A Fine
Kiss Me
Guy
Each Letter has ten subdivisions from 0 to 9
0 is hottest, 9 is coolest

10. The Spectral Types Table 15.1 The Spectral Sequence O
Stars of Orion's Belt
>30,000 K
Lines of ionized helium, weak hydrogen lines
<97 nm (ultraviolet)* B
Rigel
30,000 K-10,000 K
Lines of neutral helium, moderate hydrogen lines
nm (ultraviolet)* A
Sirius
10,000 K-7,500 K
Very strong hydrogen lines
nm (violet)* F
Polaris
7,500 K-6,000 K
Moderate hydrogen lines, moderate lines of ionized calcium
nm (blue)* G
Sun, Alpha Centauri A
6,000 K-5,000 K
Weak hydrogen lines, strong lines of ionized calcium
nm (yellow) K
Arcturus
5,000 K-3,500 K
Lines of neutral and singly ionized metals, some molecules
nm (red) M
Betelgeuse, Proxima Centauri
<3,500 K
Molecular lines strong
>830 nm (infrared)
*All stars above 6,000 K look more or less white to the human eye because they emit plenty of radiation at all visible wavelengths.

11. Stellar Luminosity The H-R Diagram
By 1915 had lots of spectra and classifications
Had a few distances from parallax
Once distance was available, luminosity and Absolute Magnitude
could be calculated.
Herzsprung and Russel, working independently both plotted
absolute magnitude (luminosity) vs classification (temperature)
The H-R Diagram

12. The H-R Diagram Plot of Brightness vs Temperature-5
Rigel
Giants
Capella
Sirius
Brightness
Procyon
Sun
Main Sequence +5
a Cen B
White Dwarfs
+10
Sirius B
Prox Cen
+15 O B A F G K M
Spectral Type