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Learn about the layers and features of the Sun, including its atmosphere, magnetic field, solar wind, and solar activity. Discover how energy production in the Sun is explained and how the three types of spectra are defined.
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EARTH SCIENCEGeology, the Environment and the Universe Chapter 29: Stars
Table Of Contents CHAPTER29 Section 29.1 The Sun Section 29.2Measuring the Stars Section 29.3Stellar Evolution Click a hyperlink to view the corresponding slides. Exit
What are the layers and features of the Sun? How is the process of energy production in the Sun explained? How are the three types of spectra defined? SECTION29.1 The Sun Essential Questions
The Sun contains most of the mass of the solar system and has many features typical of other stars. SECTION29.1 The Sun Review Vocabulary • magnetic field: the portion of space near a magnetic or current-carrying body where magnetic forces can be detected
SECTION29.1 The Sun New Vocabulary photosphere chromosphere corona solar wind sunspot solar flare prominence fusion fission
SECTION29.1 The Sun Properties of the Sun • The Sun is the largest object in the solar system, in both diameter and mass. The Sun contains more than 99 percent of all the mass in the solar system. It should not be surprising, then, that the Sun’s mass affects the motions of the planets and other objects.
SECTION29.1 The Sun Properties of the Sun • The Sun’s average density is similar to the densities of the gas giant planets. Computer models show that the density in the center of the Sun is about 1.50 × 105 kg/m3.
SECTION29.1 The Sun Properties of the Sun • The Sun’s interior is gaseous throughout because of its high temperature—about 1 × 107 K in the center. At this temperature, all of the gases are completely ionized. This means that the interior is composed only of atomic nuclei and electrons, in the state of matter known as plasma.
SECTION29.1 The Sun Please click the image above to view the interactive table.
SECTION29.1 The Sun The Sun’s Atmosphere • The outer regions of the Sun’s atmosphere are organized into layers, like a planetary atmosphere separated into different levels, and each layer emits energy at wavelengths resulting from its temperature.
SECTION29.1 The Sun The Sun’s Atmosphere Photosphere • The photosphere is the innermost layer of the Sun’s atmosphere and is also its visible surface. It has an effective temperature of 5800 K and is about 400 km thick.
SECTION29.1 The Sun The Sun’s Atmosphere Chromosphere • Outside the photosphere is the chromosphere, which is approximately 2500 km thick and has an average temperature of 15,000 K. • Usually, the chromosphere is visible only during a solar eclipse, but astronomers can use special filters to observe it when the Sun is not eclipsed.
SECTION29.1 The Sun The Sun’s Atmosphere Corona • The outermost layer of the Sun’s atmosphere, called the corona, extends several million kilometers from the outside edge of the chromosphere and usually has a temperature of about 3 to 5 million K.
SECTION29.1 The Sun The Sun’s Atmosphere Corona • The density of the gas in the corona is very low, which explains why the corona is so dim. It can be seen only when the photosphere is blocked by either special instruments, as in a coronagraph, or by the Moon during an eclipse.
SECTION29.1 The Sun The Sun’s Atmosphere Solar wind • Gas flows outward from the corona at high speeds and forms the solar wind. As this wind of charged particles, called ions, flows outward through the entire solar system, it bathes each planet in a flood of particles.
SECTION29.1 The Sun The Sun’s Atmosphere Solar wind • Charged particles in the solar wind are deflected by Earth’s magnetic field and are trapped in two huge rings, called the Van Allen belts. • The high-energy particles in these belts collide with gases in Earth’s atmosphere and cause the gases to give off light, called the aurora.
SECTION29.1 The Sun Solar Activity • Some features of the Sun change over time in a process called solar activity, which includes fountains and loops of glowing gas. Some of this gas has structure—a certain order in both time and place—driven by magnetic fields.
SECTION29.1 The Sun Solar Activity The Sun’s magnetic field and sunspots • The Sun’s magnetic field disturbs the solar atmosphere periodically and causes new features to appear. A sunspot is a dark spot on the surface of the photosphere that typically lasts two months, occurs in pairs, and has a penumbra and an umbra.
SECTION29.1 The Sun Solar Activity Solar activity cycle • Astronomers have observed that the number of sunspots changes from minimum to maximum and then back to minimum again in about 11 years. At this point, the Sun’s magnetic field reverses, so that the north magnetic pole becomes the south magnetic pole and vice versa.
SECTION29.1 The Sun Solar Activity Solar activity cycle • Because sunspots are caused by magnetic fields, the polarities of sunspot pairs reverse when the Sun’s magnetic poles reverse. Therefore, when the polarity of the Sun’s magnetic field is taken into account, the length of the cycle doubles to 22 years.
SECTION29.1 The Sun Solar Activity Other solar features • Coronal holes are often located over sunspot groups. Coronal holes are areas of low density in the gas of the corona and are the main regions from which the particles that comprise the solar wind escape.
SECTION29.1 The Sun Solar Activity Other solar features • Solar flares are violent eruptions of particles and radiation from the surface of the Sun. Highly active solar flares are associated with sunspots.
SECTION29.1 The Sun Solar Activity Other solar features • A prominence is an arc of gas ejected from the chromosphere, or gas that condenses in the Sun’s inner corona and rains back to the surface. Prominences can reach temperatures over 50,000 K and are associated with sunspots.
SECTION29.1 The Sun The Solar Interior • Fusion is the combination of lightweight atomic nuclei into heavier nuclei, such as hydrogen fusing into helium. • This is the opposite of the process of fission, which is the splitting of heavy atomic nuclei into smaller, lighter nuclei, like uranium into lead.
SECTION29.1 The Sun The Solar Interior Energy production in the Sun • In the core of the Sun, helium is a product of the process in which hydrogen nuclei fuse. • The mass of the helium nucleus is less than the combined mass of the four hydrogen nuclei, which means that mass is lost during the process.
SECTION29.1 The Sun The Solar Interior Energy production in the Sun • Albert Einstein’s special theory of relativity shows that mass and energy are equivalent, and that matter can be converted into energy and vice versa.
SECTION29.1 The Sun The Solar Interior Energy production in the Sun • The relationship between mass and energy can be expressed as E = mc2, where E is energy measured in joules, m is the quantity of mass that is converted to energy measured in kilograms, and c is the speed of light measured in m/s.
SECTION29.1 The Sun The Solar Interior Energy production in the Sun • Einstein’s special theory of relativity explains that the mass lost in the fusion of hydrogen to helium is converted to energy, which powers the Sun.
SECTION29.1 The Sun The Solar Interior Energy transport • Energy in the Sun is transferred mostly by radiation from the core outward to about 75 percent of its radius. The outer layers transfer energy in convection currents.
SECTION29.1 The Sun The Solar Interior Energy transport • As energy in the Sun moves outward, the temperature is reduced from a central value of about 1 × 107 K to its photospheric value of about 5800 K. • A tiny fraction of the immense amount of solar energy eventually reaches Earth.
SECTION29.1 The Sun The Solar Interior Solar energy on Earth • Above Earth’s atmosphere, 1354 J of solar energy is received in 1 m2/s (1354 W/m2). However, not all of this energy reaches the ground because some is absorbed and scattered by the atmosphere.
SECTION29.1 The Sun Spectra • A spectrum (plural, spectra) is visible light arranged according to wavelengths. There are three types of spectra: continuous, emission, and absorption.
SECTION29.1 The Sun Spectra • A spectrum that has no breaks in it, such as the one produced when light from an ordinary bulb is shined through a prism, is called a continuous spectrum. A continuous spectrum can also be produced by a glowing solid or liquid, or by a highly compressed, glowing gas.
SECTION29.1 The Sun Spectra • The spectrum from a noncompressed gas contains bright lines at certain wavelengths. This is called an emission spectrum, and the lines are called emission lines. The wavelengths of the visible lines depend on the element being observed because each element has its own characteristic emission spectrum.
SECTION29.1 The Sun Spectra • A spectrum produced from the Sun’s light shows a series of dark bands. These dark spectral lines are caused by different chemical elements that absorb light at specific wavelengths. This is called an absorption spectrum, and the lines are called absorption lines.
SECTION29.1 The Sun Solar Composition • Using the lines of the absorption spectra like fingerprints, astronomers have identified the elements that compose the Sun. The Sun is composed primarily of hydrogen and helium with small amounts of other gases.
SECTION29.1 The Sun Solar Composition • The Sun’s composition represents that of the galaxy as a whole. Most stars have proportions of the elements similar to the Sun.
Section Check SECTION29.1 The Sun has used only about 3 percent of its hydrogen. a.true b. false
Section Check SECTION29.1 Which is the visible surface of the Sun? a.photosphere b. corona c.chromosphere d.prominence
Section Check SECTION29.1 What is formed by gas flowing outward at a high speed from the Sun’s corona? a. prominence b.solar flare c.coronal hole d.solar wind
How are distances between stars measured? What is the difference between brightness and luminosity? What are the properties used to classify stars? SECTION29.2 Measuring the Stars Essential Questions
Stellar classification is based on measurement of light spectra, temperature, and composition. SECTION29.2 Measuring the Stars Review Vocabulary • wavelength: the distance from one point on a wave to the next corresponding point
SECTION29.2 Measuring the Stars New Vocabulary constellation binary star parsec parallax apparent magnitude absolute magnitude luminosity Hertzsprung-Russell diagram main sequence
Long ago, many civilizations looked at the brightest stars and named groups of them after animals, mythological characters, or everyday objects. These groups of stars are called constellations. Today, astronomers group stars by the 88 constellations named by ancient peoples. SECTION29.2 Measuring the Stars Patterns of Stars
Some constellations are visible throughout the year, depending on the observer’s location. Constellations that appear to rotate around one of the poles are called circumpolar constellations. Ursa Major, which contains the Big Dipper, is a circumpolar constellation for most of the northern hemisphere. SECTION29.2 Measuring the Stars Patterns of Stars
Unlike circumpolar constellations, the other constellations can be seen only at certain times of the year because of Earth’s changing position in its orbit around the Sun. SECTION29.2 Measuring the Stars Patterns of Stars
The most familiar constellations are the ones that are part of the zodiac. These twelve constellations can be seen in both the northern and southern hemispheres. SECTION29.2 Measuring the Stars Patterns of Stars
SECTION29.2 Measuring the Stars Patterns of Stars Star clusters • By measuring distances to stars and observing how their gravities interact with each other, scientists can determine which stars are gravitationally bound to each other. A group of stars that are gravitationally bound to each other is called a cluster.
SECTION29.2 Measuring the Stars Patterns of Stars Star clusters • An open cluster is a group of stars that are not densely packed. • A globular cluster is a group of stars that are densely packed into a spherical shape.
