1. Bellwork 11/10 Please turn in your bellwork sheet from last week
1. Choose a star name out of the beaker:
2. Using a computer or your device, look up:
Temperature
Luminosity
Color
Size (Dwarf, giant, super giant, ect)
3. Then, cut out a circle for each of your stars.
4. Write the information on the star & shade the circle with the star’s color

2. What can stars tell us about the universe?
Properties of Stars
What can stars tell us about the universe?

3. *Side note: Stellar = relating to a star…
Not the way we use it in common language

4. Stellar Brightness Brightness when viewed from Earth
There are 2 ways we can talk about “brightness” of a star…
1. Apparent brightness
Brightness when viewed from Earth
Decreases with distance

5. 2. Absolute brightness "True" or intrinsic brightness of a star
Does not depend on distance
Can also be measured in “luminosity” amount of radiation leaving a star
Both of these terms are “intrinsic” or “real” quantities

6. Canis Major (Great Dog) Constellation

7. How do scientists figure out this intrinsic value?
The distance will always be 10pc when measuring absolute brightness
Where do the “5’s” come from?

8. Color & Temperature of Stars
Color and temperature
Hot star
Temperature above 30,000 K
Emits short-wavelength light
Appears blue
Cool star
Temperature less than 3000 K
Emits longer-wavelength light
Appears red
Between 5000 and 6000 K
Stars appear yellow
e.g., Sun

9. Hertzsprung-Russell diagram
Shows the relation between stellar
Brightness (absolute brightness) and
Temperature
Diagram is made by plotting (graphing) each star's
Luminosity ( or absolute brightness) and

10. What observations can you make about the HR Diagram?

11. Let’s “dissect” the HR Diagram a little bit more
HR Diagram Lab
End Goals:
1. Understand how to read/interpret the HR Diagram
2. Infer how the HR Diagram helps scientists make predictions

12. Hertzsprung-Russell diagram
Parts of an H-R diagram
Main-sequence stars
Most stars are on the main sequence
Band through the center of the H-R diagram
Giants (or red giants)
Very luminous
Large
Upper-right on the H-R diagram

13. Hertzsprung-Russell diagram
Parts of an H-R diagram
Super Giants
Very large giants are called supergiants
Only a few percent of all stars
White dwarfs
Fainter than main-sequence stars
Small (approximate the size of Earth)
Lower-central area on the H-R diagram
Perhaps 10% of all stars

14. Spectral Class

15. What else does the Hertzprung-Russell diagram show us?

18. Properties of stars Binary stars Two stars orbiting one another
Stars are held together by mutual gravitation
Both orbit around a common center of mass
More than 50% of the stars in the universe are binary stars
Why are Binary stars important or worth talking about??

19. Properties of stars Stellar mass
Determined using binary stars – the center of mass is closest to the most massive star

20. Binary stars orbit each other around their common center of mass