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UNIT NINE: Matter and Motion in the Universe

UNIT NINE: Matter and Motion in the Universe. Chapter 26 The Solar System Chapter 27 Stars Chapter 28 Exploring the Universe. Chapter Twenty-Seven: Stars. 27.1 The Sun 27.2 Stars 27.3 The Life Cycle of Stars. Chapter 27.2 Learning Goals. Compare the Sun to other stars.

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UNIT NINE: Matter and Motion in the Universe

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  1. UNIT NINE: Matter and Motionin the Universe • Chapter 26 The Solar System • Chapter 27 Stars • Chapter 28 Exploring the Universe

  2. Chapter Twenty-Seven: Stars • 27.1 The Sun • 27.2 Stars • 27.3 The Life Cycle of Stars

  3. Chapter 27.2 Learning Goals • Compare the Sun to other stars. • Interpret an H-R diagram. • Explain how stars are classified.

  4. Investigation 27A Stars and Spectroscopy • Key Question: What are stars made of?

  5. 27.2 Classifying Stars • Astronomers classify stars according to: • size/mass, • temperature, • color, and • brightness.

  6. 27.2 The size of stars • Stars come in a range of sizes and masses. • Our Sun is a medium-sized star. • The largest stars, giant stars have a mass of about 60 times the mass of the Sun.

  7. 27.2 The size of stars • There are two types of giant stars. • Red giants are cooler than white stars. • Blue giant stars are hot and much more massive than our sun.

  8. 27.2 The size of stars • Stars that are smaller than the sun come in two main categories, dwarfsand neutron stars. • Sirius, the Dog Star, is the largest known white dwarf.

  9. 27.2 Temperature and color • If you look closely at the stars on a clear night, you might see a slight reddish or bluish tint to some stars. • This is because their surface temperatures are different.

  10. 27.2 Temperature and color • The color of light is related to its energy. • White light is a mixture of all colors at equal brightness.

  11. 27.2 Brightness and luminosity • Brightness, also called intensity, describes the amount of light energy per second falling on a surface.

  12. 27.2 Brightness and luminosity • For a distant source of light like a star, the brightness decreases as the inverse square of the distance.

  13. 27.2 Brightness and luminosity • Luminosity is the total amount of light given off by a star in all directions. • Luminosity is a fundamental property of a star whereas brightness depends on both luminosity and distance.

  14. 27.2 Temperature and luminosity • In the early 1900s, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell developed an important tool for studying stars. • Their graph showed luminosity on the y axis… • …and surface temperature on the x axis

  15. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: • Main sequence stars, like the Sun, are in a very stable part of their life cycle. • White dwarfs are hot and dim and cannot be seen without a telescope. • Red giants are cool and bright and some can be seen without a telescope. Can you locate blue giants on the H-R diagram?

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