Chapter Introduction Lesson 1 The View from Earth Lesson 2 The Sun and Other Stars Lesson 3 Evolution of Stars Lesson 4 Galaxies and the Universe Chapter Wrap-Up
What makes up the universe and how does gravity affect the universe?
What do you think? Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.
Do you agree or disagree? 1. The night sky is divided into constellations. 2. A light-year is a measurement of time. 3. Stars shine because there are nuclear reactions in their cores. 4. Sunspots appear dark because they are cooler than nearby areas.
Do you agree or disagree? 5. The more matter a star contains, the longer it is able to shine. 6. Gravity plays an important role in the formation of stars. 7. Most of the mass in the universe is in stars. 8. The Big Bang theory is an explanation of the beginning of the universe.
The View from Earth How do astronomers divide the night sky? What can astronomers learn about stars from their light? How do scientists measure the distance and the brightness of objects in the sky?
The View from Earth spectroscope astronomical unit light-year apparent magnitude luminosity
Looking at the Night Sky The star Polaris is almost directly above the North Pole. Earth s rotation causes other stars to appear to revolve around Polaris. CORBIS
Present-day astronomers use many ancient constellations to divide the sky into 88 regions.
Dividing the sky helps scientists communicate to others what area of sky they are studying.
Looking at the Night Sky (cont.) How do astronomers divide the night sky?
Looking at the Night Sky (cont.) Telescopes can collect more light than the human eye can. Steve Allen/Brand X Pictures Michael Matisse/Getty Images
Looking at the Night Sky (cont.) The electromagnetic spectrum is a continuous range of wavelengths.
Different parts of the electromagnetic spectrum have different wavelengths and different energies. You can see only a small part of the energy in these wavelengths.
Looking at the Night Sky (cont.) The set of wavelengths that a star emits is the star s spectrum. A spectroscope spreads light into different wavelengths. Using spectroscopes, astronomers can study stars characteristics, including temperatures, compositions, and energies.
Looking at the Night Sky (cont.) What can astronomers learn from a star s spectrum?
Measuring Distances Parallax is the apparent change in an object s position caused by looking at it from two different points. parallax from Greek parallaxis, means alteration
Astronomers use parallax to calculate how far an object in space is from Earth. The object is viewed from two extreme points in Earth s orbit.
An astronomical unit is the average distance between Earth and the Sun, about 150 million km.
Measuring Distances (cont.) A light-year is the distance light travels in 1 year. One light-year is about 10 trillion km.
Measuring Brightness The apparent magnitude of an object is a measure of how bright it appears from Earth.
Measuring Brightness (cont.) Luminosity is the true brightness of an object. The luminosity of a star, measured on an absolute magnitude scale, depends on the star s temperature and size, not its distance from Earth.
Measuring Brightness (cont.) How do scientists measure the brightness of stars?
Astronomers use ancient constellations to divide the sky into sections, also called constellations.
Different wavelengths of the electromagnetic spectrum carry different energies.
Astronomers measure distances within the solar system using astronomical units.
Which term refers to how bright an object appears from Earth? A. luminosity B. light-year C. apparent magnitude D. absolute magnitude
One light-year is equal to about how many kilometers? A. one million B. ten million C. one trillion D. ten trillion
Which term refers to the range of wavelengths a star emits? A. brightness B. luminosity C. magnitude D. spectrum
Do you agree or disagree? 1. The night sky is divided into constellations. 2. A light-year is a measurement of time.
The Sun and Other Stars How do stars shine? How are stars layered? How does the Sun change over short periods of time? How do scientists classify stars?
The Sun and Other Stars nuclear fusion star radiative zone convection zone photosphere chromosphere corona Hertzsprung- Russell diagram
How Stars Shine A star is a large ball of gas held together by gravity with a core so hot that nuclear fusion occurs. Nuclear fusion occurs when the nuclei of several atoms combine into one larger nucleus.
How Stars Shine (cont.) Nuclear fusion releases a large amount of energy. A star shines because when energy leaves a star s core, it travels throughout the star and radiates into space.
How Stars Shine (cont.) How do stars shine?
Composition and Structure of Stars Spectra of the Sun and other stars provide information about stellar composition. stellar Science Use anything related to stars Common Use outstanding, exemplary
Composition and Structure of Stars (cont.) There are three interior layers of a typical star. When first formed, all stars fuse hydrogen into helium in their cores.
Composition and Structure of Stars (cont.) The radiative zone is a shell of cooler hydrogen around a star s core. In the convection zone, hot gases move toward the surface as cooler gases move down into the interior.
Composition and Structure of Stars (cont.) What are the interior layers of a star?
Composition and Structure of Stars (cont.) Beyond the convection zone are the three layers of a star s atmosphere the photosphere, the chromosphere, and the corona.
Composition and Structure of Stars (cont.) The photosphere is the apparent surface of a star, where light energy radiates into space.
Composition and Structure of Stars (cont.) The chromosphere is the orange-red layer above the photosphere. The corona is the wide, outermost layer of a star s atmosphere.
Changing Features of the Sun: Sunspots Cooler regions of magnetic activity Seem to move as the Sun rotates Number varies on an 11-year cycle Digital Vision/PunchStock
Changing Features of the Sun: Coronal Mass Ejections (CMEs) Huge gas bubbles ejected from the corona Larger than flares May reach Earth Can cause radio blackouts NASA
Changing Features of the Sun: Prominences and Flares Prominences clouds and jets of gases forming loops into the corona Flares sudden increases in brightness, often near sunspots or prominences SOHO Consortium, ESA, NASA
Changing Features of the Sun: The Solar Wind Caused by charged particles streaming away from the Sun Extends to the edge of the solar system Causes auroras CORBIS
Groups of Stars Most stars exist in star systems bound by gravity. Many stars exist in large groupings called clusters. Stars in a cluster all formed at about the same time and are the same distance from Earth.
Classifying Stars Scientists classify stars according to their spectra. Though there are exceptions, color in most stars is related to mass.
Blue-white stars tend to have the most mass, followed by white stars, yellow stars, orange stars, and red stars.
The Hertzsprung-Russell diagram is a graph that plots luminosity against temperature of stars.
The y-axis of the H-R diagram displays increasing luminosity and the x-axis displays decreasing temperature.
Most stars exist along the main sequence.
The mass of a main-sequence star determines both its temperature and its luminosity
Classifying Stars (cont.) What is the Hertzsprung- Russell diagram?
Hot gas moves up and cool gas moves down in the Sun s convection zone.
Sunspots are relatively dark areas on the Sun that have strong magnetic activity. Globular clusters contain hundreds of thousands of stars.
Which term refers to the wide, outermost layer of a star s atmosphere? A. radiative zone B. corona C. convection zone D. chromosphere
Scientists classify stars according to which of these? A. mass B. size C. spectra D. temperature
What color of stars tend to have the most mass? A. yellow B. red C. orange D. blue-white
Do you agree or disagree? 3. Stars shine because there are nuclear reactions in their cores. 4. Sunspots appear dark because they are cooler than nearby areas.
Evolution of Stars How do stars form? How does a star s mass affect its evolution? How is star matter recycled in space?
Evolution of Stars nebula white dwarf supernova neutron star black hole
Life Cycle of a Star Stars form deep inside clouds of gas and dust. A cloud of gas and dust is a nebula. nebula from Latin nebula, means mist or little cloud
Life Cycle of a Star (cont.) Star-forming nebulae are cold, dense, and dark. Photo courtesy of NASA/Corbis
Life Cycle of a Star (cont.) Gravity causes the densest parts to collapse, forming regions called protostars. Over many thousands of years, the energy produced by protostars heats the gas and dust surrounding them.
Life Cycle of a Star (cont.) How do stars form?
Life Cycle of a Star (cont.) A star becomes a main-sequence star as soon as it begins to fuse hydrogen into helium. Low-mass stars stay on the main sequence for billions of years, and high-mass stars are there for only a few million years.
Life Cycle of a Star (cont.) When a star s hydrogen supply is nearly gone, the star leaves the main sequence and begins the next stage of its life cycle. All stars form in the same way, but stars die in different ways, depending on their masses. Massive stars eventually become red supergiants.
End of a Star After helium in the cores of lower-mass stars is gone, the stars cast off their gases, exposing their cores. The core eventually becomes a white dwarf, a hot, dense, slowly cooling sphere of carbon. This is what is expected to happen to the Sun.
The Sun will remain on the main sequence for 5 billion more years.
When the Sun becomes a red giant for the second time, it will probably absorb Earth and push Mars and Jupiter outward.
When the Sun becomes a white dwarf, the solar system will be a cold, dark place.
End of a Star (cont.) Very massive stars can explode in a supernova, which destroys the star. Iron in the core does not fuse and the core collapses quickly under the force of gravity. The normal space within atoms is eliminated, leaving a dense core of neutrons, or a neutron star.
End of a Star (cont.) For the most massive stars, atomic forces holding neutrons together are not strong enough to overcome so much mass in such a small volume. Gravity is too strong, and the matter crushes into a black hole. A black hole is an object whose gravity is so great that no light can escape.
End of a Star (cont.) How does a star s mass determine if it will become a white dwarf, a neutron star, or a black hole?
Recycling Matter When a star becomes a white dwarf, it casts off hydrogen and helium gases in its outer layers. The expanding, cast-off matter of a white dwarf is a planetary nebula. During a supernova, a massive star comes apart sending a shock wave into space.
Recycling Matter (cont.) The expanding cloud of dust and gas is called a supernova remnant. Gravity causes recycled gases and other matter to clump together in nebulae and form new stars and planets.
Recycling Matter (cont.) How do stars recycle matter?
Iron is formed in the cores of the most massive stars.
The Sun will become a red giant in about 5 billion years. Matter is recycled in supernovae.
What term refers to clouds of gas and dust where stars form? A. white dwarf B. supernova C. nebula D. black hole
What type of star is a hot, dense, slowly cooling sphere of carbon? A. neutron star B. red giant C. supernova D. white dwarf
Which of these is an object whose gravity is so great that no light can escape? A. white dwarf B. supernova C. nebula D. black hole
Do you agree or disagree? 5. The more matter a star contains, the longer it is able to shine. 6. Gravity plays an important role in the formation of stars.
Galaxies and the Universe What are the major types of galaxies? What is the Milky Way, and how is it related to the solar system? What is the Big Bang theory?
Galaxies and the Universe galaxy dark matter Big Bang theory Doppler shift
Galaxies Galaxies are huge collections of stars. galaxy from Greek galactos, means milk
Galaxies (cont.) Gravity holds stars and galaxies together. When astronomers examine how galaxies rotate and gravitationally interact, they find that most of the matter in galaxies is invisible. Matter that emits no light at any wavelength is dark matter.
Types of Galaxies: Spiral Galaxies Spiral arms of stars, gas, and dust extend from central disk. Spiral galaxies have a central bulge. NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics) A spherical halo surrounds the disk.
Types of Galaxies: Elliptical Galaxies Elliptical galaxies have a spherical or elliptical shape and no internal structure. They contain more older stars than spiral galaxies, and may have formed as spiral galaxies merged. JPL/NASA
Types of Galaxies: Irregular Galaxies Irregular galaxies are oddly shaped and contain many young stars. Local Group Galaxies Survey Team, NOAO, AURA, NSF
Galaxies (cont.) What are the major types of galaxies?
The Milky Way The solar system is in the Milky Way, a spiral galaxy that contains gas, dust, and almost 200 billion stars. The Milky Way is a member of the Local Group, a cluster of about 30 galaxies.
The Milky Way (cont.) Where is Earth in the Milky Way?
The Big Bang Theory According to the Big Bang theory, the universe began from one point billions of years ago and has been expanding ever since. What is the Big Bang theory?
The Big Bang Theory (cont.) Most scientists agree that the universe is 13-14 billion years old. Scientists observe how space stretches by measuring the speed at which galaxies move away from the Earth.
The Big Bang Theory (cont.) When light travels away from you, its wavelength stretches out, shifting to the red end of the electromagnetic spectrum. The shift to a different wavelength is called the Doppler shift.
Doppler Shift
By studying interacting galaxies, scientists have determined that most mass in the universe is dark matter. The Sun is one of billions of stars in the Milky Way.
When an object moves away, its light stretches out, just as a siren s sound waves stretch out as the siren moves away.
What term refers to matter that emits no light at any wavelength? A. clusters B. dark matter C. H-R matter D. light matter
The Milky Way is a member of the Local Group which is a cluster of about how many galaxies? A. 5 B. 30 C. 200 D. 1 billion
Approximately what is the age of the universe? A. 1-2 million years B. 9-10 million years C. 4-5 billion years D. 13-14 billion years
Do you agree or disagree? 7. Most of the mass in the universe is in stars. 8. The Big Bang theory is an explanation of the beginning of the universe.
Key Concept Summary Interactive Concept Map Chapter Review Standardized Test Practice
The universe is made up of stars, gas, and dust, as well as invisible dark matter. Material in the universe is pulled by gravity into galaxies, including our own Milky Way galaxy.
Lesson 1: The View from Earth The sky is divided into 88 constellations. Astronomers learn about the energy, distance, temperature, and composition of stars by studying their light. Astronomers measure distances in space in astrological units and in light-years. They measure star brightness as apparent magnitude and as luminosity.
Lesson 2: The Sun and Other Stars Stars shine because of nuclear fusion in their cores. Stars have a layered structure they conduct energy through their radiative zones and their convection zones and release the energy at their photospheres. Sunspots, prominences, flares, and coronal mass ejections are temporary phenomena on the Sun. Astronomers classify stars by their temperatures and luminosities.
Lesson 3: Evolution of Stars Stars are born in clouds of gas and dust called nebulae. What happens to a star when it leaves the main sequence depends on its mass. Matter is recycled in the planetary nebulae of white dwarfs and the remnants of supernovae.
Lesson 4: Galaxies and the Universe The three major types of galaxies are spiral, elliptical, and irregular. The Milky Way is the spiral galaxy that contains the solar system. The Big Bang theory explains the origin of the universe.
Which of these describes the average distance between Earth and the Sun? A. astronomical unit B. Doppler shift C. light-year D. solar distance
The true brightness of an object can also be referred to as which of these? A. apparent magnitude B. astronomical unit C. luminosity D. spectrum
Which term refers to the apparent surface of a star? A. chromosphere B. convection zone C. corona D. photosphere
Which is an enormous explosion that destroys a star? A. supernova B. nebula C. Hertzsprung-Russell event D. Doppler shift
The universe began from one point billions of years ago and has been expanding ever since, according to which of these? A. Big Bang theory B. Doppler shift C. H-R diagram D. law of magnitude
Which of these refers to the distance light travels in one year? A. astronomical unit B. light-year C. solar magnitude D. 2 trillion km
Which of these spreads light into different wavelengths? A. telescope B. spectroscope C. photosphere D. dark matter
Which of these is the shell of cooler hydrogen above a star s core? A. radiative zone B. photosphere C. corona D. convection zone
Which of these is the dense core of matter left from a supernova? A. white dwarf B. neutron star C. nebula D. black hole
Which term refers to huge collections of stars? A. galaxies B. dark matter C. clusters D. astronomical units