Section1 Stars Chapter J2 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.

Section1 Stars Chapter J2 Composition of Stars continued • The Colors of LightA 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.

Section1 Stars Chapter J2 Composition of Stars continued • Making an IDEmission lines are lines made when certain wavelengths,of light, or colors, are given off by hot gasses. • Each elements produces a unique set of emission lines, which allows them to be used to identify the elements in a star.

Section1 Stars Chapter J2 Emission Lines of Elements

Section1 Stars Chapter J2 Classifying Stars • Differences in TemperatureStars are now classified by how hot they are. • Differences in BrightnessThe brightest star, Sirius, has a magnitude of -1.4. The dimmest star that can be seen with a telescopes has a magnitude of 29.

Section1 Stars Chapter J2 Magnitude of Stars in Big Dipper

Section1 Stars Chapter J2 How Bright Is That Star? • Apparent MagnitudeThe brightness of a light or star is called apparent magnitude. • Absolute MagnitudeAbsolute magnitude is the actual brightness of a star.

Section1 Stars Chapter J2 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. • Parallax is the apparent shift in the position of an object when viewed from different locations. Measuring parallax enables scientists to calculate the distance between a star and the Earth.

Section1 Stars Chapter J2

Section1 Stars Chapter J2 Finding the Distance to Stars: Parallax Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

Section1 Stars Chapter J2 Motions of Stars • The Apparent Motion of StarsIf you look at the night sky long enough, the stars also appear to move. • The Actual Motion of StarsThe apparent motion of the sun and stars in our sky is due to Earth’s rotation. But each star is also moving in space. Their actual movements, however, are difficult to see.

Section1 Stars Chapter J2 Apparent Motion of Stars

Section1 Stars Chapter J2 Actual Motion of Stars

Section2 The Life Cycle of Stars Chapter J2 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 1987A and the Large Magellanic Cloud taken before the explosion. Record and illustrate your answers in your science journal.

Section2 The Life Cycle of Stars Chapter J2 Objectives • Describedifferent types of stars. • Describethe 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.

Section2 The Life Cycle of Stars Chapter J2 The Beginning and End of Stars • The BeginningA 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 EndStars 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.

Section2 The Life Cycle of Stars Chapter J2 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 StarsAfter 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.

Section2 The Life Cycle of Stars Chapter J2 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 know 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.

Section2 The Life Cycle of Stars Chapter J2 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 DiagramThe 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.

Section2 The Life Cycle of Stars Chapter J2 H-R Diagram

Section2 The Life Cycle of Stars Chapter J2

Section2 The Life Cycle of Stars Chapter J2 When Stars Get Old • Supernovas A supernovais a gigantic explosion in which a massive blue star collapses. • Neutron Stars and PulsarsA star that has collapsed under gravity to the point at which all of its particles are neutrons is called aneutron star. If a neutron star is spinning, it is called apulsar.

Section2 The Life Cycle of Stars Chapter J2 When Stars Get Old, continued • Black HolesSometimes the leftovers of a supernova are so massive that they collapse to form a black hole. Ablack holeis an object that is so massive that even light cannot escape its gravity.

Section3 Galaxies Chapter J2 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.

Section3 Galaxies Chapter J2 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..

Section3 Galaxies Chapter J2 • A galaxyis a collection of stars, dust, and gas held together by gravity. • Types of Galaxies • Spiral Galaxieshave a bulge at the center and spiral arms. • The Milky WayAstronomers think that our solar system is in a spiral galaxy.

Section3 Galaxies Chapter J2 Types of Galaxies, continued • Elliptical GalaxiesAbout one-third of all galaxies are simply massive blobs of stars. These are called elliptical galaxies. • Irregular Galaxies Galaxies that do not fit into any other class are called irregular galaxies.

Section3 Galaxies Chapter J2 Contents of Galaxies • Gas CloudsA large clouds of gas and dust in interstellar space is called anebula. • Star ClustersAglobular clusteris a tight group of stars that looks like a ball and contains up to 1 million stars. • Anopen clusteris a group of stars that are close together relative to surrounding stars.

Section3 Galaxies Chapter J2

Section3 Galaxies Chapter J2 Origin of the Galaxies • Because if takes light time to travel through space, looking at distant galaxies reveals what early galaxies looked like. • QuasarsAvery luminous, starlike object that generates energy at a high rate is called aquasar. Some scientists think that quasars may be the core of young galaxies that are in the process of forming.

Section4 Formation of the Universe Chapter J2 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.

Section4 Formation of the Universe Chapter J2 Objectives • Describe the big bang theory. • Explainevidence used to support the big bang theory. • Describe the structure of the universe.

Section4 Formation of the Universe Chapter J2 Objectives, continued • Describetwo ways scientists calculate the age of the universe. • Explain what will happen if the universe expands forever.

Section4 Formation of the Universe Chapter J2 • 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.

Section4 Formation of the Universe Chapter J2 Universal Expansion Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

Section4 Formation of the Universe Chapter J2 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 radiationleft over from the big bang.

Section4 Formation of the Universe Chapter J2 Big Bang Theory

Section4 Formation of the Universe Chapter J2 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 radiationleft over from the big bang.

Section4 Formation of the Universe Chapter J2 The Structure of the Universe

Section4 Formation of the Universe Chapter J2 How Old Is the Universe? • Age of the UniverseScientist 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.

Section4 Formation of the Universe Chapter J2 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.

Stars, Galaxies, and the Universe Chapter J2 Concept Map Use the following terms to complete the concept map on the next slide:

Stars, Galaxies, and the Universe Chapter J2

End of Chapter J2 Show

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