1. How light from the stars can tell us (almost) everything about them!
The H-R Diagram
How light from the stars can tell us (almost) everything about them!

2. How Hot Is It?
Photometry: measuring a star’s temperature by studying its color
What color is the hottest? The coldest?
Hottest: Blue/Violet
Coldest: Red

3. NO!!! YES!!!

4. Stellar Spectroscopy
Can identify the chemical composition AND the temperature of stars!
How?
Excitation energy of electrons in their shells – Quantum Mechanics

5. Spectral Classification
Using spectroscopy to relate directly to stellar surface temperature.
Fixed by Annie Jump Cannon
Classifies stars by temperature from hottest to coolest
Directly related to a star’s color

6. 40,000 K
O B A F G K M
2,000 K

7. O B A F G K M There are sub-ranges Our Sun? A G2 star 0 – 10
0 = hottest
10 = coolest
For example:
B4 is a hotter star than B8
F9 is hotter than G2
Our Sun?
A G2 star

8. Patterns Emerge When Luminosity (power) is plotted against Temperature
1911 – Ejnar Hertzsprung
1913 – Henry Russell

9. Stars don’t have random temperatures and colors
Stars don’t have random temperatures and colors! They are directly related!

11. Luminosity Class The measure of Watts produced by the star
Also able to be seen by spectroscopy
White Dwarfs usually not included (no fusion)

12. The H-R Diagram plots FOUR aspects of stars
The 2 Pairs are Directly Related: Spectral Class & Temperature Luminosity & Magnitude

13. Remember Stellar Lifecycles?
Interactive HR Diagram

14. HR Diagram Family Project
Create your own HR Diagram using a family of people or objects!
Follow a theme: real life, TV shows, movies, book characters, etc.
Can be digital or on paper
Must demonstrate four different stages of star life:
Protostar
Main Sequence
Giant/Supergiant
White Dwarf/NS/Black Hole