UNIT NINE: Matter and Motion in the Universe

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

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

5. Chapter 27.1 Learning Goals • Explore the properties of the Sun. • Identify unique zones of the Sun and describe what happens in each area. • Discuss applications of solar energy.

6. 27.1 The Sun • The Sun is is a giant, hot ball of gas held together by gravity. • The Sun is medium-sized compared with other stars in the universe. Approximately 1 million planet Earths could fit inside the Sun!

7. 27.1 The Sun • Gravity squeezes the density of a star so tightly in the core that the electrons are stripped away and the bare nuclei of atoms almost touch each other. • Nuclear fusion occurs.

8. 27.1 The Sun • In the process, huge amounts of energy are given off. • Because of its mass, the Sun’s gravitational force is strong enough to hold the entire solar system in orbit.

10. 27.1 Anatomy of the sun • The apparent surface of the Sun that we can see from a distance is called the photosphere, which means “sphere of light.” • Just above it is the chromosphere. • This is a very hot layer of plasma, a high-energy state of matter.

11. 27.1 Anatomy of the sun • The coronais the outermost layer of the sun’s atmosphere, extending millions of kilometers beyond the sun. • Sunspots are areas of gas that are cooler than the gases around them.

12. 27.1 Features of the sun • Occasionally, large “loops” of gas called prominencescan be seen jumping up from groups of sunspots.

13. 27.1 Features of the sun • Solar windis an electrically charged mixture of protons and electrons that cause magnetic storms. • Auroras, called the northern lights, occur when layers of our atmosphere are energized by solar winds.

14. 27.1 Solar energy • Solar energyis a term that refers to radiant energy from the Sun. • The radiant energy of the Sun reaches Earth in the form of electromagnetic waves. • We can use solar energy to heat buildings and generate electricity.

15. 27.1 Solar energy • Buildings that use passive solar heatingare designed to trap sunlight. • Glass traps warm air, causing a “greenhouse effect.”

16. 27.1 Solar energy • Photovoltaic (or PV) cells are devices that convert sunlight directly into electricity. • Solar cells are found on calculators, watches, or certain outdoor light fixtures.

17. 27.1 More about the Sun’s energy • In 1905, Albert Einstein proposed that matter can be converted into energy. • His famous equation shows how huge amounts of energy can be created from a smaller mass.

18. 27.1 More about the Sun’s energy • The amount of this energy from the Sun that reaches the outer edge of Earth’s atmosphere is known as the solar constant. • The accepted value is 1,386 watts per square meter (W/m2), or about thirteen 100-watt light bulbs per square meter of surface.

19. Optional* Investigation 27C Efficiency of a Solar Cell • Key Question: How can we use energy from the sun to generate electricity?