The Sun’s Energy

1. Chapter 29 Chapter 29 Section 1 Structure of t The Sun’s Energy Composition of the Sun • Using a device called a spectrograph, scientists break up the sun’s light into a spectrum. • 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.

2. Chapter 29 Section 1 Structure of the Sun 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.

3. Chapter 29 Section 1 Structure of the Sun The Sun’s Energy, continued Nuclear Fusion • nuclear fusion - the process by which nuclei of small atoms combine to form a new, more massive nucleus; the process releases energy • 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.

4. Chapter 29 Section 1 Structure of the Sun 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.

5. Chapter 29 Section 1 Structure of the Sun 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.

6. Chapter 29 Section 1 Structure of the Sun The Sun’s Energy, continued The diagram below shows nuclear fusion.

7. Chapter 29 Section 1 Structure of the Sun 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. • The energy released during the three steps of nuclear fusion causes the sun to shine and gives the sun its high temperature.

8. Chapter 29 Section 1 Structure of the Sun 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 = mc2

9. Chapter 29 Section 1 Structure of the Sun Mass Changing into Energy • In Einstein’s equation E = mc2, 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 explain the huge quantities of energy produced by the sun.

10. Chapter 29 Section 1 Structure of the Sun 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 the core, the radiative zone, and the convective zone. • 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 15,000,000ºC. • The core is made up entirely of ionized gas, and is 10 times as dense as iron.

11. Chapter 29 Section 1 Structure of the Sun The Sun’s Interior, continued The Radiative Zone radiative zone - the zone of the sun’s interior that is between the core and the convective zone and in which energy moves by radiation • 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, energy moves outward in the form of electromagnetic waves, or radiation.

12. Chapter 29 Section 1 Structure of the Sun The Sun’s Interior, continued The Convective Zone Convective zone - the region of the sun’s interior that is between the radiative zone and the photosphere and in which energy is carried upward by convection • The convective zone surrounds the radiative zone. The temperature of the convective zone is about 2,000,000ºC. • Energy produced in the core moves through this zone by convection. • Convection is the transfer of energy by moving matter.

13. Chapter 29 Section 1 Structure of the Sun The Sun’s Interior, continued The diagram below shows the layers of the sun.

14. The Sun’s Interior • Where in the sun does nuclear fusion occur? • What conditions in this part of the sun’s interior cause nuclear fusion to happen? • How does the energy produced by nuclear fusion escape the sun? • How does energy move through the sun’s radiative zone? • What function does the sun’s convective zone perform?

15. Chapter 29 Section 1 Structure of the Sun 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 uppermost region of solar gases. • The sun’s atmosphere has three layers: the photosphere, the chromosphere, and the corona.

16. Chapter 29 Section 1 Structure of the Sun The Sun’s Atmosphere The Photosphere photosphere - the visible surface of the sun • 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.

17. Chapter 29 Section 1 Structure of the Sun The Sun’s Atmosphere, continued The Chromosphere chromosphere - the thin layer of the sun that is just above the photosphere and that glows a reddish color during eclipses • 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.

18. Chapter 29 Section 1 Structure of the Sun The Sun’s Atmosphere, continued The Sun’s Outer Parts corona - the outermost layer of the sun’s atmosphere • The corona is a huge region of gas that has a temperature above 1,000,000ºC. • As the corona expands, electrons and electrically charged particles called ions stream out into space. • These particles make up solar wind, which flows outward from the sun to the rest of the solar system.

19. Chapter 29 Section 1 Structure of the Sun The Sun’s Atmosphere

20. Chapter 29 Section 2 Solar Activity Sunspots sunspot - a dark area of the photosphere of the sun that is cooler than the surrounding areas and that has a strong magnetic field. • The movements of gases within the sun’s convective zone and the movements caused by the sun’s rotation produce magnetic fields. • These magnetic fields cause convection to slow in parts of the convective zone.

21. Chapter 29 Section 2 Solar Activity Sunspots • Slower convection causes a decrease in the amount of gas that is transferring energy from the core of the sun to these regions of the photosphere. • Because less energy is being transferred, these regions of the photosphere are considerably cooler than surrounding regions, and form areas of the sun that appear darker than their surrounding regions. • These, cooler, darker areas are called sunspots.

22. Chapter 29 Section 2 Solar Activity The Sunspot Cycle • Observations of sunspots have shown that the sun rotates. • The numbers and positions of sunspots vary in a cycle that lasts about 11 years. • Sunspots initially appear in groups about midway between the sun’s equator and poles. The number of sunspots increases over the next few years until it reaches a peak of 100 of more sunspots. • After the peak, the number of sunspots begins to decrease until it reaches a minimum.

23. Chapter 29 Section 2 Solar Activity Solar Ejections • Other solar activities are affected by the sunspot cycle, such as the solar-activity cycle. • The solar-activity cycle is caused by the changing solar magnetic field. • This cycle is characterized by increases and decreases in various types of solar activity, including solar ejections. • Solar ejections are events in which the sun emits atomic particles.

24. Chapter 29 Section 2 Solar Activity Solar Ejections, continued Prominences prominence - a loop of relatively cool, incandescent gas that extends above the photosphere. • Solar ejections include prominences, solar flares, and coronal mass ejections. • Prominences are huge arches of glowing gases that follow the curved lines of the magnetic force from a region of one magnetic force to a region of the opposite magnetic polarity.

25. Chapter 29 Section 2 Solar Activity Solar Ejections, continued Solar Flares solar flare - an explosive release of energy that comes from the sun and that is associated with magnetic disturbances on the sun’s surface • Solar flares are the most violent of all solar disturbances. • Solar flares release the energy stored in the strong magnetic fields of sunspots. This release can lead to the formation of coronal loops.

26. Chapter 29 Section 2 Solar Activity Solar Ejections, continued Coronal Mass Ejections coronal mass ejection - a part of coronal gas that is thrown into space from the sun • Some of the particles from a solar flare escape into space, increasing the strength of the solar wind. • Particles also escape as coronal mass ejections. The particles in the ejection can cause disturbances to Earth’s magnetic field. • These disturbances have been known to interfere with radio communications, satellites, and even cause blackouts.

27. Chapter 29 Section 2 Solar Activity Auroras aurora - colored light produced by charged particles from the solar wind and from the magnetosphere that react with and excite the oxygen and nitrogen of Earth’s upper atmosphere; usually seen in the sky near Earth’s magnetic poles. • Auroras are the result of the interaction between the solar wind and Earth’s magnetosphere. • Auroras are usually seen close to Earth’s magnetic poles because electrically charged particles are guided toward earth’s magnetic poles by Earth’s magnetosphere.

28. Chapter 29 Maps in Action Maps in Action SXT Composite Image of the Sun

29. Chapter 30 Section 1 Chapter 30 Analyzing Starlight star - a large celestial body that is composed of gas and that emits light. • Nuclear fusion is the combination of light atomic nuclei to form heavier atomic nuclei • Astronomers learn about stars by analyzing the light that the stars emit. • Starlight passing through a spectrograph produces a display of colors and lines called a spectrum.

30. Section 1 Characteristics of Stars Chapter 30 Analyzing Starlight, continued • All stars have dark-line spectra, which are bands of color crossed by dark lines where the color is diminished. • A star’s dark-line spectrum reveals the star’s composition and temperature. • Stars are made up of different elements in the form of gases. • Because different elements absorb different wavelengths of light, scientists can determine the elements that make up a star by studying its spectrum.

31. Section 1 Characteristics of Stars Chapter 30 The Compositions of Stars • Scientists have learned that stars are made up of the same elements that compose Earth. • The most common element in stars is hydrogen. • Helium is the second most common element in star. • Small quantities of carbon, oxygen, and nitrogen are also found in stars.

32. Section 1 Characteristics of Stars Chapter 30 The Temperatures of Stars • The temperature of most stars ranges from 2,800˚C to 24,000˚C. • Blue stars have average surface temperatures of 35,000˚C. • Yellow stars, such as the sun, have surface temperatures of about 5,500˚C. • Red stars have average surface temperatures of 3,000˚C.

33. Classification of Stars COLOR SURFACE TEMPERATURE(oC) EXAMPLES Blue Above 30,000 Lacetae Blue-white 10,000-30,000 Rigel, Spica White 7,500-10,000 Vega, Sirius Yellow-white 6,000-7,500 Canopus, Procyon Yellow 5,000-6,000 Sun, Capella Orange 3,500-5,000 Arcturus, Aldebaran Red Less than 3,500 Betelgeuse, Antares

34. Section 1 Characteristics of Stars Chapter 30 The Sizes and Masses of Stars • Stars vary in size and mass. • Stars such as the sun are considered medium-sized stars. The sun has a diameter of 1,390,000 km. • Most stars visible from Earth are medium-sized stars. • Many stars also have about the same mass as the sun, however some stars may be more or less massive.

37. Section 1 Characteristics of Stars Chapter 30 Stellar Motion Apparent Motion • The apparent motion of stars is the motion visible to the unaided eye. Apparent motion is caused by the movement of Earth. • The rotation of Earth causes the apparent motion of stars sees as though the stars are moving counter-clockwise around the North Star. • Earth’s revolution around the sun causes the stars to appear to shift slightly to the west every night.

38. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Circumpolar Stars • Some stars are always visible in the night sky. These stars never pass below the horizon. • In the Northern Hemisphere, the movement of these stars makes them appear to circle the North Star. • These circling stars are called circumpolar stars.

39. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Actual Motion of Stars • Doppler effect - an observed change in the frequency of a wave when the source or observer is moving • The spectrum of a star that is moving toward or away from Earth appears to shift, due to the Doppler effect. • Stars moving toward Earth are shifted slightly toward blue, which is called blue shift. • Stars moving away from Earth are shifted slightly toward red, which is called red shift.

40. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued The spectrum of a star that is moving toward or away from Earth appears to shift, as shown in the diagram below.

41. Section 1 Characteristics of Stars Chapter 30 Distances to Stars • light-year - the distance that light travels in one year. • Distances between the stars and Earth are measured in light-years. • parallax - an apparent shift in the position of an object when viewed from different locations. • For relatively close stars, scientists determine a star’s distance by measuring parallax.

42. Section 1 Characteristics of Stars Chapter 30 Stellar Brightness • Apparent magnitude - the brightness of a star as seen from the Earth. • The apparent magnitude of a star depends on both how much light the star emits and how far the star is from Earth. • Absolute magnitude - the brightness that a star would have at a distance of 32.6 light-years from Earth • The brighter a star is, the lower the number of its absolute magnitude.

43. Apparent MagnitudeIn this system, a difference of 5 magnitudes corresponds to a factor of 100 in brightness. Negative numbers are assigned for objects brighter than magnitude +1.

44. Section 1 Characteristics of Stars Chapter 30 Stellar Brightness The lower the number of the star on the scale shown on the diagram below, the brighter the star appears to observers.

45. Absolute magnitude is the brightness an object would have if it were placed at a distance of 10 pc.

46. Chapter 30 Section 2 Stellar Evolution Classifying Stars • Main sequence - the location on the H-R diagram where most stars lie; it has a diagonal pattern from the lower right to the upper left. • One way scientists classify stars is by plotting the surface temperatures of stars against their luminosity. The H-R diagram is the graph that illustrates the resulting pattern. • Astronomers use the H-R diagram to describe the life cycles of stars. Most stars fall within a band that runs diagonally through the middle of the H-R diagram. These stars are main sequence stars.

47. Chapter 30 Section 2 Stellar Evolution Classifying Stars, continued • Main sequence the location on the H-R diagram where most stars lie; it has a diagonal pattern from the lower right to the upper left. • One way scientists classify stars is by plotting the surface temperatures of stars against their luminosity. The H-R diagram is the graph that illustrates the resulting pattern. • Astronomers use the H-R diagram to describe the life cycles of stars. Most stars fall within a band that runs diagonally through the middle of the H-R diagram. These stars are main sequence stars.

48. Chapter 30 Section 2 Stellar Evolution Classifying Stars, continued