1. Group Project 1 is due on Friday; Only 1 paper per group
Group Project 1 is due on Friday; Only 1 paper per group. Any late HW3s- no later than Friday, then solutions posted.

2. Holy cow, that's everything!
We want to know:
How hot are stars?
How BIG are stars (size)?
How massive are stars?
What are stars made of?
How much energy do stars emit?
Where does that energy come from?
How far away are stars?
T = 2.9x106/l
Eclipsing binaries/parallax
Binaries
Spectral lines: H, He
Luminosity
H Fusion: E=mc2
Parallax, eclipsing binaries.
Holy cow, that's everything!
Plus spin, the structure of the Sun, neutrinos, etc.

3. Reminder: How to make a star brighter: Lap=4pR2T4/d2
Make it hotter: E~T4
Make it bigger: E~R2
Make it closer: E~1/d2
Hotter is most powerful.

4. Question: in the following spectra; 1) Which star is the hottest
Question: in the following spectra; 1) Which star is the hottest? 2) Which star is the coolest?

5. 500
600
700nm
Hottest A1 B1 A2 B2 A3 B3 A4 B4
Coolest
=nm x 10

6. 3) What does the size of the dot represent in a picture like this?

7. 3) What does the size of the dot represent in a picture like this?
Brightness

8. 4) What does the color represent?

9. 4) What does the color represent?
Temperature

10. 5) What is the difference between Star A and Star B?
(Other than temperature or color and assuming the dots are the same size.) A B C E D

11. 5) What is the difference between Star A and Star B?
(Other than temperature or color and assuming the dots are the same size.)
Star A must be smaller than Star B A B C E D

12. 6) What is the difference between Star B and Star D?
(Assuming they are the same temperature.) A B C E D

13. 6) What is the difference between Star B and Star D?
(Assuming they are the same temperature.)
Star D must be larger than Star B A B C E D

14. 7) What is the difference between Star C and Star E?
(Other than temperature and assuming the dots are the same size.) A B C E D

15. 7) What is the difference between Star C and Star E?
(Other than temperature and assuming the dots are the same size.)
Star C must be larger. A B C E D

16. 8) Which stars are most common in this image: large dots or small dots (brighter stars or fainter stars)?

17. 8) Which stars are most common in this image: large dots or small dots (brighter stars or fainter stars)?
Small

18. 9) Which stars are most common in this image: red, blue, or white stars?

19. 9) Which stars are most common in this image: red, blue, or white stars?
Red, or maybe white. A B C E D

20. 10) Based on your previous 2 answers, which stars are the most common?
11) Describe them in terms of temperature and size. A B C E D

21. 10) Based on your previous 2 answers, which stars are the most common?
Small, red or white
11) Describe them in terms of temperature and size.
Faint and cooler. A B C E D

22. So blue, bright stars are rare!
10) Based on your previous 2 answers, which stars are the most common?
Small, red or white
11) Describe them in terms of temperature and size.
Faint and cooler. A B C E D
So blue, bright stars are rare!

23. Classifying stars C D A B

24. This is what random (unrelated) looks like
In science, if we can measure 2 things, we plot them against each other and look for relationships.
This is what random (unrelated) looks like

25. What’s the underlying relationship
If we plot height versus mass (weight) of people, we get the graph below.
What’s the underlying relationship

26. There is an underlying reason for the relationship.
If we plot height versus mass (weight) of people, we get the graph below.
As people grow up (age), they gain weight. A child (shorter) weighs less than an adult.
There is an underlying reason for the relationship.

27. For stars, in an image we can measure 2 things: brightness and color
For stars, in an image we can measure 2 things: brightness and color. So make a plot for that!

28. Regions in this diagram correspond to different kinds of stars.

29. Hertzsprung-Russell Diagram of nearby stars
Hertzsprung-Russell Diagram of nearby stars. They had parallaxes for these stars.
Blue
Red

30. They noticed that stars do not appear randomly on this graph, but rather form groups. Why?
Blue
Red

31. The stars fall into groups
The stars fall into groups. The group where we see the most stars is called the
Main Sequence.
Stars of similar temperature, but brighter are called Red Giants, and smaller stars are called
white dwarfs.