Classificagtion of Stars:Classificagtion of Stars:The H-R diagramThe H-R diagram

“The stars are distant and unobtrusive, but bright and enduring as our fairest and most memorable experiences.”

Henry David Thoreau (1849)

Are Stars similar to our Sun?How far away are they?Where did they come from?What do they do?Do they live forever?

Reading AssignmentReading Assignment

All Chapter 9All Chapter 9

Discussion QuestionDiscussion QuestionHow can I understand the How can I understand the

performance of CARSperformance of CARS

P = P(Weight; Power; Overall P = P(Weight; Power; Overall Built)Built)

Make a plot that shows the general Make a plot that shows the general relationship between Weight and relationship between Weight and Horsepower of cars.Horsepower of cars.

-now add to your plot sports cars…-… racing cars…-… and economy models

This kind of plots summarizes in a powerful waygeneral features of most cars

Classification of StarsClassification of Stars

1) Collect information ona large sample of stars.

2) Measure their luminosities(need the distance!)

3) Measure their surface temperatures(need their spectra)

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

The Main Sequence

- all main sequencestars fuse H into Hein their cores

- this is the definingcharacteristic of a main sequence star.

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

Red Giants

- Red Giant starsare very large, cooland quite bright.

Ex. Betelgeuse is100,000 times moreluminous than the Sunbut is only 3,500K onthe surface. It’s radiusis 1,000 times that of theSun.

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

White Dwarfs

- White Dwarfsare hot but sincethey are so small,they are not veryluminous.

The Hertzsprung-Russell The Hertzsprung-Russell DiagramDiagram

Lifetimeof Star

Shorter

Longer

More mass,more fuel,very fast burning.

Less mass,less fuel,slow, steady burning.

How do we know the age of a star?

ThinkThinkSUV vs a Honda CivicSUV vs a Honda Civic

The H-R diagramThe H-R diagram

Which is the faintest? the sun, an O star, a white dwarf, or a red giant?Which of these star is the hottest?What are Sun-like stars (0.4 M < M < 8 M) in

common?What about red dwarfs (0.08 M < M < 0.4 M) ?Where do stars spend most of their time?

O

What is the order of stellar evolution of a star like the Sun?

To calculate a star's radius, you must know its

1) temperature and luminosity.

2) chemical composition and temperature.

3) color and chemical composition.

4) luminosity and surface gravity.

L=4πR2 σT4

3) 4 times larger

4) the same

1) ½ times as large

2) ¼ times as large

If a star is half as hot as our Sun, but has the same luminosity, how large is its radius compared to the Sun?

L=4πR2 σT4

What is burning in stars?What is burning in stars?

Gasoline Gasoline Nuclear fissionNuclear fission Nuclear fusionNuclear fusion Natural gas Natural gas