Presentation on theme: "Objectives Vocabulary Explore the structure of the Sun."— Presentation transcript:
1Objectives Vocabulary Explore the structure of the Sun. Describe the solar activity cycle and how the Sun affects Earth.Compare the different types of spectra.Vocabularyphotospherechromospherecoronasolar windsunspotsolar flareprominencefusionfissionspectrum
2The SunThe SunThrough observations and probes, such as the Solar Heliospheric Observatory (SOHO) and the Ulysses mission, astronomers have begun to unravel the mysteries of the Sun.Astronomers still rely on computer models for an explanation of the interior of the Sun because the interior cannot be directly observed.
3The SunProperties of the SunThe Sun is the largest object in the solar system, in both size and mass.The Sun contains more than 99 percent of all the mass in the solar system, which allows it to control the motions of the planets and other objects.Models show that the density in the center of the Sun is about 1.50 × 105 kg/m3.
4The SunProperties of the SunThe solar interior is gaseous throughout because of its high temperature—about 1 × 107 K in the center.Many of the gases are in a plasma state, meaning that they are completely ionized and composed only of atomic nuclei and electrons.The outer layers of the Sun are not quite hot enough to be plasma.
5The SunThe Sun’s AtmosphereThe photosphere, approximately 400 km in thickness, is the lowest layer of the Sun’s atmosphere.This is the visible surface of the Sun because most of the light emitted by the Sun comes from this layer.The average temperature of the photosphere is about 5800 K (5500 C or 9980 F).
6The SunThe Sun’s AtmosphereThe chromosphere, which is above the photosphere and approximately 2500 km in thickness, has a temperature of nearly K at the top.The corona, which is the top layer of the Sun’s atmosphere, extends several million kilometers southward from the top of the chromosphere and has a temperature range of 1 million to 2 million degrees K.
7The Sun’s Atmosphere Solar Wind Gas flows outward from the corona at high speeds and forms the solar wind.Solar wind consists of charged particles, or ions, that flow outward through the entire solar system, bathing each planet in a flood of particles.The charged particles are trapped in two huge rings in Earth’s magnetic field, called the Van Allen belts, where they collide with gases in Earth’s atmosphere, causing an aurora.
8The SunSolar ActivityThe Sun’s magnetic field disturbs the solar atmosphere periodically and causes new features to appear in a process called solar activity.Sunspots are cooler areas that form on the surface of the photosphere due to magnetic disturbances, which appear as dark spots.
9Solar Activity Solar Activity Cycle The SunSolar ActivitySolar Activity CycleThe number of sunspots changes regularly, and on average reaches a maximum number every 11.2 years.The length of the solar activity cycle is 22.4 years.The solar activity cycle starts with minimum spots and progresses to maximum spots.The Sun’s magnetic field then reverses in polarity, and the spots start at a minimum number and progress to a maximum number again.The magnetic field then switches back to the original polarity and completes the solar activity cycle.
10Solar Activity Other Solar Features The SunSolar ActivityOther Solar FeaturesCoronal holes, often located over sunspot groups, are areas of low density in the gas of the corona.Solar flares are violent eruptions of particles and radiation from the surface of the Sun that are associated with sunspots.When these particles reach Earth, they can interfere with communications and damage satellites.A prominence, sometimes associated with flares, is an arc of gas that is ejected from the chromosphere, or gas that condenses in the inner corona and rains back to the surface.
11Solar Activity Impact on Earth The SunSolar ActivityImpact on EarthSome scientists have found evidence of subtle climate variations within 11-year periods.There were severe weather changes on Earth during the latter half of the 1600s when the solar activity cycle stopped and there were no sunspots for nearly 60 years.Those 60 years were known as the “Little Ice Age” because the weather was very cold in Europe and North America during those years.
12The SunThe Solar InteriorFusion occurs within the core of the Sun where the pressure and temperature are extremely high.Fusion is the combining of lightweight nuclei, such as hydrogen, into heavier nuclei.Fission, the opposite of fusion, is the splitting of heavy atomic nuclei into smaller, lighter atomic nuclei.In the core of the Sun, helium is a product of the process in which hydrogen nuclei fuse.At the Sun’s rate of hydrogen fusing, it is about halfway through its lifetime, with about another 5 billion years left.
13The Solar Interior Energy from the Sun The quantity of energy that arrives on Earth every day from the Sun is enormous.Above Earth’s atmosphere, 1354 J of energy is received in 1 m2 per second (1354 W/m2).Not all of this energy reaches the ground because some is absorbed and scattered by the atmosphere.
14The Solar Interior Solar Zones The SunThe Solar InteriorSolar ZonesEnergy produced in the core of the Sun gets to the surface through two zones in the solar interior.In the radiative zone, which is above the core, energy is transferred from particle to particle by radiation, as atoms continually absorb energy and then re-emit it.Above the radiative zone, in the convective zone, moving volumes of gas carry the energy the rest of the way to the Sun’s surface through convection.
16Spectra A spectrum is visible light arranged according to wavelengths. The SunSpectraA spectrum is visible light arranged according to wavelengths.There are three types of spectra:A continuous spectrum is a spectrum that has no breaks in it that can be produced by a glowing solid or liquid, or by a highly compressed, glowing gas.An emission spectrum has bright lines in it called emission lines that depend on the element being observed.An absorption spectrum has dark lines called absorption lines which are caused by different chemical elements that absorb light at specific wavelengths.
17The SunSpectraAbsorption is caused by a cooler gas in front of a source that emits a continuous spectrum.By comparing laboratory spectra of different gases with the dark lines in the solar spectrum, it is possible to identify the elements that make up the Sun’s outer layers.
18The SunSpectraA continuous spectrum is produced by a hot solid, liquid, or dense gas. When a cloud of gas is in front of this hot source, an absorption spectrum is produced. A cloud of gas without a hot source behind it will produce an emission spectrum.
19The SunSolar CompositionThe Sun consists of hydrogen, about 73.4 percent by mass, and helium, 25 percent, as well as a small amount of other elements.This composition is very similar to that of the gas giant planets.The Sun’s composition represents that of the galaxy as a whole.
20The SunSection Assessment1. Match the following terms with their definitions.___ photosphere___ corona___ chromosphere___ sunspotA. the middle layer of the Sun’s atmosphereB. the outermost layer of the Sun’s atmosphereC. cooler region on the Sun’s surface that forms due to magnetic irregularitiesD. the lowest layer of the Sun’s atmosphere
21The SunSection Assessment2. How can we determine what gases are in the outer layers of the Sun’s atmosphere?
22The SunSection Assessment3. Identify whether the following statements are true or false.______ The Sun contains more than 99 percent of all mass in the solar system.______ Most visible light from the sun originates in the chromosphere.______ The energy released by the Sun originates through nuclear fission.______ Mass can be converted into energy.
24Objectives Vocabulary Describe star distribution and distance. Measuring the StarsObjectivesDescribe star distribution and distance.Classify the types of stars.Summarize the interrelated properties of stars.Vocabularyconstellationbinary starparallaxapparent magnitudeabsolute magnitudeluminosityHertzsprung-Russell diagrammain sequence
25Measuring the StarsGroups of StarsConstellations are the 88 groups of stars named after animals, mythological characters, or everyday objects.Circumpolar constellations can be seen all year long as they appear to move around the north or south pole.Summer, fall, winter, and spring constellations can be seen only at certain times of the year because of Earth’s changing position in its orbit around the Sun.
26Groups of Stars Star Clusters Measuring the StarsGroups of StarsStar ClustersAlthough stars may appear to be close to each other, very few are gravitationally bound to one other.By measuring distances to stars and observing how they 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.In an open cluster, the stars are not densely packed.In a globular cluster, stars are densely packed into a spherical shape.
27Groups of Stars Binaries Measuring the StarsGroups of StarsBinariesA binary star is two stars that are gravitationally bound together and that orbit a common center of mass.More than half of the stars in the sky are either binary stars or members of multiple-star systems.Astronomers are able to identify binary stars through several methods.Accurate measurements can show that its position shifts back and forth as it orbits the center of mass.In an eclipsing binary, the orbital plane of a binary system can sometimes be seen edge-on from Earth.
28Stellar Position and Distances Measuring the StarsStellar Position and DistancesAstronomers use two units of measure for long distances.A light-year (ly) is the distance that light travels in one year, equal to × 1012 km.A parsec (pc) is equal to 3.26 ly, or × 1013 km.
29Stellar Position and Distances Measuring the StarsStellar Position and DistancesTo estimate the distance of stars from Earth, astronomers make use of the fact that nearby stars shift in position as observed from Earth.Parallax is the apparent shift in position of an object caused by the motion of the observer.As Earth moves from one side of its orbit to the opposite side, a nearby star appears to be shifting back and forth.
30Stellar Position and Distances Measuring the StarsStellar Position and DistancesThe distance to a star, up to 500 pc using the latest technology, can be estimated from its parallax shift.
31Basic Properties of Stars Measuring the StarsBasic Properties of StarsThe basic properties of stars include diameter, mass, brightness, energy output (power), surface temperature, and composition.The diameters of stars range from as little as 0.1 times the Sun’s diameter to hundreds of times larger.The masses of stars vary from a little less than 0.01 to 20 or more times the Sun’s mass.
32Basic Properties of Stars Measuring the StarsBasic Properties of StarsMagnitudeOne of the most basic observable properties of a star is how bright it appears.The ancient Greeks established a classification system based on the brightnesses of stars.The brightest stars were given a ranking of +1, the next brightest +2, and so on.
33Basic Properties of Stars Measuring the StarsBasic Properties of StarsApparent MagnitudeApparent magnitude is based on the ancient Greek system of classification which rates how bright a star appears to be.In 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.
34Basic Properties of Stars Measuring the StarsBasic Properties of StarsAbsolute MagnitudeApparent magnitude does not actually indicate how bright a star is, because it does not take distance into account.Absolute magnitude is the brightness an object would have if it were placed at a distance of 10 pc.
35Basic Properties of Stars Measuring the StarsBasic Properties of StarsLuminosityLuminosity is the energy output from the surface of a star per second.The brightness we observe for a star depends on both its luminosity and its distance.Luminosity is measured in units of energy emitted per second, or watts.The Sun’s luminosity is about 3.85 × 1026 W.
36Measuring the StarsSpectra of StarsStars also have dark absorption lines in their spectra and are classified according to their patterns of absorption lines.
37Spectra of Stars Classification Measuring the StarsSpectra of StarsClassificationStars are assigned spectral types in the following order: O, B, A, F, G, K, and M.Each class is subdivided into more specific divisions with numbers from 0 to 9.The classes correspond to stellar temperatures, with the O stars being the hottest and the M stars being the coolest.The Sun is a type G2 star, which corresponds to a surface temperature of about 5800 K.
38Spectra of Stars Classification Measuring the StarsSpectra of StarsClassificationAll stars, including the Sun, have nearly identical compositions—about 73 percent of a star’s mass is hydrogen, about 25 percent is helium, and the remaining 2 percent is composed of all the other elements.The differences in the appearance of their spectra are almost entirely a result of temperature effects.B5 starF5 starK5 starM5 star
39Spectra of Stars Wavelength Shift Measuring the StarsSpectra of StarsWavelength ShiftSpectral lines are shifted in wavelength by motion between the source of light and the observer due to the Doppler effect.If a star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths, or blueshifted.If the star is moving away, the wavelengths become longer, or redshifted.
40Measuring the StarsSpectra of StarsWavelength Shift
41Spectra of Stars Wavelength Shift Measuring the StarsSpectra of StarsWavelength ShiftThe higher the speed, the larger the shift, and thus spectral line wavelengths can be used to determine the speed of a star’s motion.Astronomers can learn only about the portion of a star’s motion that is directed toward or away from Earth.
42Spectra of Stars H-R Diagrams Measuring the StarsSpectra of StarsH-R DiagramsA Hertzsprung-Russell diagram, or H-R diagram, demonstrates the relationship between mass, luminosity, temperature, and the diameter of stars.An H-R diagram plots the absolute magnitude on the vertical axis and temperature or spectral type on the horizontal axis.
43Spectra of Stars H-R Diagrams Measuring the StarsSpectra of StarsH-R DiagramsThe main sequence, which runs diagonally from the upper-left corner to the lower-right corner of an H-R diagram, represents about 90 percent of stars.Red giants are large, cool, luminous stars plotted at the upper-right corner.White dwarfs are small, dim, hot stars plotted in the lower-left corner.
45Measuring the StarsSection Assessment1. Match the following terms with their definitions.___ binary star___ absolute magnitude___ luminosity___ parallaxA. the energy output from the surface of a star per secondB. when two stars are gravitationally bound and orbit a common center of massC. the brightness an object would have if placed at a set distanceD. an apparent shift in the position of an object caused by the motion of the observer
46Measuring the StarsSection Assessment2. How can astronomers measure the speed at which a star is moving?
47Measuring the StarsSection Assessment3. Identify whether the following statements are true or false.______ The full Moon has less brightness than Venus on the absolute magnitude scale.______ Luminosity of stars is a relatively consistent stellar property.______ Around two-thirds of the stars in the sky are either binary stars or members of multi-star systems.______ The Sun is part of the main sequence.
49Objectives Vocabulary Stellar EvolutionObjectivesExplain how astronomers learn about the internal structure of stars.Describe how the Sun will change during its lifetime and how it will end up.Compare the evolutions of stars of different masses.Vocabularynebulaprotostarneutron starsupernovablack hole
50Basic Structure of Stars Stellar EvolutionBasic Structure of StarsThe mass and the composition of a star determine nearly all its other properties.Hydrostatic equilibrium is the balance between gravity squeezing inward and pressure from nuclear fusion and radiation pushing outward.This balance, which is governed by the mass of a star, must hold for any stable star; otherwise, the star would expand or contract.
51Basic Structure of Stars Stellar EvolutionBasic Structure of StarsFusionInside a star, the density and temperature increase toward the center, where energy is generated by nuclear fusion.Stars on the main sequence all produce energy by fusing hydrogen into helium, as the Sun does.Stars that are not on the main sequence either fuse different elements in their cores or do not undergo fusion at all.
52Basic Structure of Stars Stellar EvolutionBasic Structure of StarsFusionFusion reactions involving elements other than hydrogen can produce heavier elements, but few heavier than iron.The energy produced according to the equation E = mc2 stabilizes a star by producing the pressure needed to counteract gravity.
53Stellar Evolution and Life Cycles A star changes as it ages because its internal composition changes as nuclear fusion reactions in the star’s core convert one element into another.As a star’s core composition changes, its density increases, its temperature rises, and its luminosity increases.When the nuclear fuel runs out, the star’s internal structure and mechanism for producing pressure must change to counteract gravity.
54Stellar Evolution and Life Cycles Star FormationA nebula (pl. nebulae) is a cloud of interstellar gas and dust.Star formation begins when the nebula collapses on itself as a result of its own gravity.As the cloud contracts, its rotation forces it into a disk shape.A protostar is a hot condensed object that forms at the center of the disk that will become a new star.
55Stellar Evolution and Life Cycles Star Formation
56Stellar Evolution and Life Cycles Fusion BeginsEventually, the temperature inside a protostar becomes hot enough for nuclear fusion reactions to begin converting hydrogen to helium.Once this reaction begins, the star becomes stable because it then has sufficient internal heat to produce the pressure needed to balance gravity.The object is then truly a star and takes its place on the main sequence according to its mass.
57Stellar EvolutionThe Sun’s Life CycleWhat happens during a star’s life cycle depends on its mass.It takes about 10 billion years for a star with the mass of the Sun to convert all of the hydrogen in its core into helium.When the hydrogen in its core is gone, a star has a helium center and outer layers made of hydrogen-dominated gas.Some hydrogen continues to react in a thin layer at the outer edge of the helium core.
58Stellar EvolutionThe Sun’s Life CycleThe energy produced in the thin hydrogen layer forces the outer layers of the star to expand and cool and the star becomes a red giant.While the star is a red giant, it loses gas from its outer layers while its core becomes hot enough, at 100 million K, for helium to react and form carbon.When the helium in the core is all used up, the star is left with a core made of carbon.
59The Sun’s Life Cycle A Nebula Once Again Stellar EvolutionThe Sun’s Life CycleA Nebula Once AgainA star of the Sun’s mass never becomes hot enough for carbon to react, so the star’s energy production ends at this point.The outer layers expand once again and are driven off entirely by pulsations that develop, becoming a shell of gas called a planetary nebula.In the center of a planetary nebula, the core of the star remains as a white dwarf made of carbon.
60The Sun’s Life Cycle Pressure in White Dwarfs Stellar EvolutionThe Sun’s Life CyclePressure in White DwarfsA white dwarf is stable because it is supported by the resistance of electrons being squeezed close together and does not require a source of heat to be maintained.A star that has less mass than that of the Sun has a similar life cycle, except that helium may never form carbon in the core, and the star ends as a white dwarf made of helium.
61Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsA massive star begins its life high on the main sequence with hydrogen being converted to helium.A massive star undergoes many reaction phases and produces many elements in its interior.The star becomes a red giant several times as it expands following the end of each reaction stage.
62Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsAs more shells are formed by the fusion of different elements, the star expands to a larger size and becomes a supergiant.A massive star loses much of its mass during its lifetime.White dwarf composition is determined by how many reaction phases the star went through before reactions stopped.
63Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsSupernovaeA star that begins with a mass between about 8 and 20 times the Sun’s mass will end up with a core that is too massive to be supported by electron pressure.Once no further energy-producing reactions can occur, the core of the star violently collapses in on itself and protons and electrons in the core merge to form neutrons.A neutron star results from the resistance of neutrons to being squeezed, which creates a pressure that halts the collapse of the core.
64Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsSupernovaeA neutron star has a mass of 1.5 to 3 times the Sun’s mass but a radius of only about 10 km.Infalling gas rebounds when it strikes the hard surface of the neutron star and explodes outward.A supernova (pl. supernovae) is a massive explosion in which the entire outer portion of the star is blown off and elements that are heavier than iron are created.
65Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsSupernovae
66Life Cycles of Massive Stars Stellar EvolutionLife Cycles of Massive StarsBlack HolesA star that begins with more than about 20 times the Sun’s mass will not be able to form a neutron star.The resistance of neutrons to being squeezed is not great enough to stop the collapse, so the core of the star simply continues to collapse forever, compacting matter into a smaller and smaller volume.A black hole is a small, extremely dense remnant of a star whose gravity is so immense that not even light can escape its gravity field.
67Stellar EvolutionSection Assessment1. Match the following terms with their definitions.___ nebula___ protostar___ supernova___ black holeA. a cloud of interstellar gas and dustB. small, extremely dense remnant of a star with immense gravityC. a hot, condensed object that eventually will begin nuclear fusion.D. a massive explosion that blows off the outer portion of a massive star
68Stellar EvolutionSection Assessment2. How is a neutron star different from a white dwarf?
69Stellar EvolutionSection Assessment3. Identify whether the following statements are true or false.______ The Sun will likely produce a supernova.______ Black holes are likely smaller than 10 km in diameter.______ Planets form from planetary nebula.______ All stable stars have hydrostatic equilibrium.______ The Sun will become a red giant in about 5 million years.
71Section 30.1 Study GuideSection 30.1 Main IdeasThe Sun contains most of the mass in the solar system and is made up primarily of hydrogen and helium.Astronomers learn about conditions inside the Sun by a combination of observation and theoretical models.The Sun’s atmosphere consists of the photosphere, the chromosphere, and the corona.The Sun has a 22-year activity cycle caused by reversals in its magnetic field polarities.Sunspots, solar flares, and prominences are active features of the Sun.The solar interior consists of the core, where fusion of hydrogen into helium occurs, and the radiative and convective zones.
72Section 30.2 Study GuideSection 30.2 Main IdeasPositional measurements of the stars are important for measuring distances through stellar parallax shifts.Stellar brightnesses are expressed in the systems of apparent and absolute magnitude.Stars are classified according to the appearance of their spectra, which indicate the surface temperatures of stars.The H-R diagram relates the basic properties of stars: class, mass, temperature, and luminosity.
73Section 30.3 Study GuideSection 30.3 Main IdeasThe mass of a star determines its internal structure and its other properties.Gravity and pressure balance each other in a star.If the temperature in the core of a star becomes high enough, elements heavier than hydrogen but lighter than iron can fuse together.Stars such as the Sun end up as white dwarfs. Stars up to about 8 times the Sun’s mass also form white dwarfs after losing mass. Stars with masses between 8 and 20 times the Sun’s mass end as neutron stars, and more massive stars end as black holes.A supernova occurs when the outer layers of the star bounce off the neutron star core, and explode outward.