1. The Sun Section 1 Section 1: Structure of the Sun Preview Objectives The Sun’s Energy Nuclear Fusion Mass Changing into Energy The Sun’s Interior The Sun’s Atmosphere Structure of the Sun

2. The Sun Section 1 Objectives Explain how the sun converts matter into energy in its core. Compare the radiative and convective zones of the sun. Describe the three layers of the sun’s atmosphere.

3. The Sun Section 1 The Sun’s Energy Composition of the Sun *. Dark lines form in the spectra of stars when gases in the stars’ outer layers absorb specific wavelengths of the light that passes through the layers. By studying the spectrum of a star, scientists can determine the amounts of elements that are present in a star’s atmosphere.

4. The Sun Section 1 The Sun’s Energy, continued Composition of the Sun Because each element produces a unique pattern of spectral lines, astronomers can match the spectral lines of starlight to those of Earth’s elements, and identify the elements in the star’s atmosphere. Both hydrogen and helium occur in the sun. About 75% of the sun’s mass is hydrogen, and hydrogen and helium together make up about 99% of the sun’s mass. The sun’s spectrum reveals that the sun contains traces of almost all other chemical elements.

5. The Sun Section 1 The Sun’s Energy, continued Nuclear Fusion nuclear fusion * Nuclear fusion occurs inside the sun. Nuclei of hydrogen atoms are the primary fuel for the sun’s fusion. Nuclear fusion produces most of the suns’ energy and consists of three steps.

6. The Sun Section 1 The Sun’s Energy, continued Nuclear Fusion In the first step, two hydrogen nuclei, or protons, collide and fuse. In this step, the positive charge of one of the protons is neutralized as that proton emits a particle called a positron. As a result, the proton becomes a neutron and changes the original two protons into a proton-neutron pair.

7. The Sun Section 1 The Sun’s Energy, continued Nuclear Fusion In the second step, another proton combines with this proton-neutron pair to produce a nucleus made up of two protons and one neutron. In the third step, two nuclei made up of two protons and one neutron collide and fuse. As this fusion happens, two protons are released. The remaining two protons and two neutrons are fused together and form a helium nucleus. At each step, energy is released.

8. The Sun Section 1 The Sun’s Energy, continued The diagram below shows nuclear fusion.

9. The Sun Section 1 The Sun’s Energy, continued The Final Product One of the final products of the fusion of hydrogen in the sun is always a helium nucleus. The helium nucleus has about 0.7% less mass than the hydrogen nuclei that combined to form it do. The lost mass is converted into energy during the series of fusion reactions that forms helium. *.

10. The Sun Section 1 Nuclear Fusion

11. The Sun Section 1 Mass Changing into Energy The sun’s energy comes from fusion, and the mass that is lost during fusion becomes energy. In 1905, Albert Einstein proposed that a small amount of matter yields a large amount of energy. This proposal was part of Einstein’s special theory of relativity. This theory included the equation: E = mc 2

12. The Sun Section 1 Mass Changing into Energy In Einstein’s equation E = mc 2, E represents energy produced; m represents the mass; and c represents the speed of light, which is about 300,000 km/s. Einstein’s equation can be used to calculate the amount of energy produced from a given amount of matter. By using Einstein’s equation, astronomers were able to *.

13. The Sun Section 1 Reading check How did the equation E = mc 2 help scientists understand the energy of the sun? Einstein’s equation helped scientists understand the source of the sun’s energy. The equation explained how the sun could produce huge amounts of energy without burning up.

14. The Sun Section 1 The Sun’s Interior The Core Careful studies of motions on the sun’s surface have supplied more detail about what is happening inside the sun. The parts of the sun include *. At the center of the sun is the core. The core makes up 25% of the sun’s total diameter of 1,390,000 km. The temperature of the core is about 15,000,000 ºC. The core is made up entirely of ionized gas, and is 10 times as dense as iron.

15. The Sun Section 1 The Sun’s Interior, continued The Radiative Zone radiative zone * The radiative zone of the sun surrounds the core. The temperature of the radiative zone ranges from about 2,000,000ºC to 7,000,000 ºC. In the radiative zone, *.

16. The Sun Section 1 The Sun’s Interior, continued The Convective Zone Convective zone * The convective zone surrounds the radiative zone. The temperature of the convective zone is about 2,000,000ºC. *.

17. The Sun Section 1 The Sun’s Interior, continued The diagram below shows the layers of the sun.

18. The Sun Section 1 The Sun’s Atmosphere The sun’s atmosphere surrounds the convective zone of the sun’s core. Because the sun is made of gases, the term atmosphere refers to *. The sun’s atmosphere has three layers*.

19. The Sun Section 1 The Sun’s Atmosphere The Photosphere photosphere * Photosphere means “sphere of light.” The photosphere of the sun is the innermost layer of the sun’s atmosphere. The photosphere is made of gases that have risen from the convective zone. The temperature in the photosphere is about 6,000ºC. Much of the energy given off from the photosphere is in the form of visible light.

20. The Sun Section 1 The Sun’s Atmosphere Reading Check What layers make up the sun’s atmosphere? The sun’s atmosphere consists of the photosphere, the chromosphere, and the corona.

21. The Sun Section 1 The Sun’s Atmosphere, continued The Chromosphere chromosphere * The chromosphere lies just above the photosphere. The chromosphere’s temperature ranges from 4,000°C to 50,000 °C. The gases of the chromosphere move away from the photosphere, forming narrow jets of hot gas that shoot outward and then fade away within a few minutes.

22. The Sun Section 1 The Sun’s Atmosphere, continued The Sun’s Outer Parts corona * The corona is a huge region of gas that has a temperature above 1,000,000ºC. As the corona expands, *. These particles make up *.

23. The Sun Section 1 The Sun’s Atmosphere

24. The Sun Section 1 Structure of the Sun