Chapter 19 Stars Galaxies and the Universe Table
Chapter 19 Stars, Galaxies, and the Universe Table of Contents Section 2 The Life Cycle of Stars Section 3 Galaxies Section 4 Formation of the Universe
Chapter 19 Section 1 Stars Color of Stars • Because a blue flame is hotter than a yellow or red flame, we can conclude that blue stars are hotter than yellow or red stars.
Chapter 19 Section 1 Stars Composition of Stars • A star is made of different elements in the form of gases. • The gases in the atmosphere of a star absorb different wavelengths of light depending on which elements make up the gases. • The light from a star indicates which elements make up that star.
Chapter 19 Section 1 Stars Composition of Stars continued • The Colors of Light A prism breaks white light into a rainbow of colors called a spectrum. • An instrument called a spectrograph is used to break a star’s light into a spectrum. The spectrum of a star will vary depending on which elements are present.
Chapter 19 Section 1 Stars Classifying Stars • Differences in Temperature Stars are now classified by how hot they are. • Differences in Brightness The brightest star, Sirius, has a magnitude of -1. 4. The dimmest star that can be seen with a microscope has a magnitude of 29.
Chapter 19 Section 1 Stars Distance to the Stars • Because stars are so far away, astronomers use light-years to measure the distances from Earth to the stars. A light year is the distance that light travels in a year.
Chapter 19 Section 2 The Life Cycle of Stars Bellringer Supernovas represent the “death” of stars that exceed a certain mass. In a few seconds, a supernova can release more energy than it previously did in its entire existence. Look at the photographs of Supernova 1987 A and the Large Magellanic Cloud taken before the explosion. Record and illustrate your answers in your science journal.
Chapter 19 Section 2 The Life Cycle of Stars Objectives • Describe different types of stars. • Describe the quantities that are plotted in the H-R diagram. • Explain how stars at different stages in their life cycle appear on the H-R diagram.
Chapter 19 Section 2 The Life Cycle of Stars The Beginning and End of Stars • The Beginning A star enters the first stage of its life cycle as a ball of gas and dust. Gravity pulls the gas and dust together, and hydrogen changes to helium in a processes called nuclear fusion. • The End Stars usually lose material slowly, but sometimes they can lose material in a big explosion. Much of a star’s material returns to space, where it sometimes forms new stars.
Chapter 19 Section 2 The Life Cycle of Stars Different Types of Stars • Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and age. A star’s classification can change as it ages. • Main-Sequence Stars After a star forms, it enters the second and longest stage of its life cycle known as the main sequence. Energy is generated in the core as hydrogen atoms fuse into helium atoms.
Chapter 19 Section 2 The Life Cycle of Stars Different Types of Stars, continued • Giants and Supergiants After the main-sequence stage, a star can enter the third stage of its life cycle. A red giant, as it is known, is a large, reddish star late in its life cycle. • In this third stage, a star can become a red giant. As the center of the star shrinks, the atmosphere of the star grows very large and cools to form a red giant or a red supergiant.
Chapter 19 Section 2 The Life Cycle of Stars A Tool for Studying Stars • The H-R Diagram the Hertzprung-Russell diagram is a graph that shows the relationship between a star’s surface temperature and absolute magnitude. • Reading the H-R Diagram The diagonal pattern on the H-R diagram where most stars lie is called the main sequence. Find the diagonal pattern in the H-R Diagram on the next two slides.
Chapter 19 Section 2 The Life Cycle of Stars H-R Diagram
Chapter 19 Section 2 The Life Cycle of Stars
Chapter 19 Section 2 The Life Cycle of Stars When Stars Get Old • Supernovas A supernova is a gigantic explosion in which a massive blue star collapses. • Neutron Stars and Pulsars A star that has collapsed under gravity to the point at which all of its particles are neutrons is called a neutron star. If a neutron star is spinning, it is called a pulsar.
Chapter 19 Section 2 The Life Cycle of Stars When Stars Get Old, continued • Black Holes Sometimes the leftovers of a supernova are so massive that they collapse to form a black hole. A black hole is an object that is so massive that even light cannot escape its gravity.
Chapter 19 Section 3 Galaxies Bellringer Look at the photograph of a spiral galaxy. • Describe the evidence that indicates that the galaxy is rotating. • What other objects have you seen look similar to a spiral galaxy? Do they rotate? Record your answers in your science journal.
Chapter 19 Section 3 Galaxies Objectives • Identify three types of galaxies. • Describe the contents and characteristics of galaxies. • Explain why looking at distant galaxies reveals what young galaxies looked like. .
Chapter 19 Section 3 Galaxies • A galaxy is a collection of stars, dust, and gas held together by gravity. Types of Galaxies • Spiral Galaxies have a bulge at the center and spiral arms. • The Milky Way Astronomers think that our solar system is in a spiral galaxy.
Chapter 19 Section 3 Galaxies Types of Galaxies, continued • Elliptical Galaxies About one-third of all galaxies are simply massive blobs of stars. These are called elliptical galaxies. • Irregular Galaxies that do not fit into any other class are called irregular galaxies.
Chapter 19 Section 3 Galaxies Contents of Galaxies • Gas Clouds A large clouds of gas and dust in interstellar space is called a nebula. • Star Clusters A globular cluster is a tight group of stars that looks like a ball and contains up to 1 million stars. • An open cluster is a group of stars that are close together relative to surrounding stars.
Chapter 19 Section 3 Galaxies
Chapter 19 Section 3 Galaxies Origin of the Galaxies • Because if takes light time to travel through space, looking at distant galaxies reveals what early galaxies looked like. • Quasars A very luminous, starlike object that generates energy at a high rate is called a quasar. Some scientists think that quasars may be the core of young galaxies that are in the process of forming.
Chapter 19 Section 4 Formation of the Universe Bellringer Look at Figure 1. The first image represents the initial explosion of the big bang, and the following images represent the expansion of the universe and the formation of the galaxies. Describe the differences between the images. Record your answers in your science journal.
Chapter 19 Section 4 Formation of the Universe Objectives • Describe the big bang theory. • Explain evidence used to support the big bang theory. • Describe the structure of the universe.
Chapter 19 Section 4 Formation of the Universe Objectives, continued • Describe two ways scientists calculate the age of the universe. • Explain what will happen if the universe expands forever.
Chapter 19 Section 4 Formation of the Universe • Cosmology is the study of the origin, properties, processes, and evolution of the universe. Universal Expansion • Galaxy Movement To understand how the universe formed, scientists study the movement of galaxies. • A Raisin-Bread Model The universe, like the rising raisin bread dough, is expanding. Think of the raisins in the dough as galaxies. As the universe expands, the galaxies move farther apart.
Chapter 19 Section 4 Formation of the Universal Expansion Click below to watch the Visual Concept You may stop the video at any time by pressing the Esc key.
Chapter 19 Section 4 Formation of the Universe The Big Bang Theory • A Tremendous Explosion The theory that the universe began with a tremendous explosion is called the big bang theory. • Cosmic Background Radiation In 1964, two scientists using a huge antenna accidentally found radiation coming from all directions in space. One explanation for this radiation is that it is cosmic background radiation left over from the big bang.
Chapter 19 Section 4 Formation of the Universe Big Bang Theory
Chapter 19 The Structure of the Universe Section 4 Formation of the Universe
Chapter 19 Section 4 Formation of the Universe How Old Is the Universe? • Age of the Universe Scientist use to methods to study the age of the universe. • By measuring the distance between Earth and various galaxies, scientists can predict the rate of expansion and calculate the age of the universe. • Because the universe must at least be as old as the oldest stars it contains, the ages of the stars provide a clue to the age of the universe.
Chapter 19 Section 4 Formation of the Universe A Forever Expanding Universe • The expansion of the universe depends on the amount of matter it contains. A large enough quantity of matter would cause gravity to stop the expansion. The universe could start collapsing. • Scientist now think that there may not be enough matter in the universe, so the universe would continue to expand forever and become cold and dark as all the stars die.
End of Chapter 19
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