Chapter 15 Preview Section 1 Stars Stars, Galaxies, and the Universe Preview Section 1 Stars Section 2 The Life Cycle of the Stars Section 3 Galaxies Section 4 Formation of the Universe Concept Map

Chapter 15 Bellringer List ways that stars differ from one another. Section 1 Stars Bellringer List ways that stars differ from one another. How is the sun like other stars? How is it different? Write your answers in your Science Journal.

Chapter 15 What You Will Learn Section 1 Stars What You Will Learn Stars differ in size, temperature, composition, brightness, and color. Distances between stars are very large and are measured in light-years.

Chapter 15 Section 1 Stars Color of Stars The color of a star indicates the star’s temperature. Red stars are the coolest, and blue stars are the hottest. If two stars differ in color, you can conclude that they differ in temperature too.

Chapter 15 Composition of Stars Section 1 Stars Composition of Stars Astronomers use an instrument called a spectroscope to separate a star’s light into a spectrum (plural, spectra). A spectrum is the band of colors produced when white light passes through a prism.

Composition of Stars, continued Chapter 15 Section 1 Stars Composition of Stars, continued A continuous spectrum shows all of the colors, while an absorption spectrum shows which wavelengths of light are absorbed. The spectrum of a star is an absorption spectrum because the atmosphere of the star absorbs certain portions of the light produced by the star.

Composition of Stars, continued Chapter 15 Section 1 Stars Composition of Stars, continued The pattern of lines in a star’s absorption spectrum is unique to that star. A star’s absorption spectrum can be used to determine the elements in that star’s atmosphere. Stars are made of mostly hydrogen and helium gases.

Composition of Stars, continued Chapter 15 Stars, Galaxies, and the Universe Composition of Stars, continued

Chapter 15 Classifying Stars Section 1 Stars Classifying Stars Stars are now classified by how hot they are. Temperature differences between stars result in color differences that can be seen. For example, class O stars are blue—the hottest stars.

Classifying Stars, continued Chapter 15 Section 1 Stars Classifying Stars, continued Magnitude is used to compare the brightness of one object with the brightness of another object. To express the brightness of stars, astronomers use a system of magnitudes.

Classifying Stars, continued Chapter 15 Section 1 Stars Classifying Stars, continued Positive magnitude numbers represent dim stars. Negative magnitude numbers represent bright stars. The brightest star in the night sky, Sirius, has a magnitude of -1.4.

Chapter 15 Stars, Galaxies, and the Universe Classifying Stars

Chapter 15 How Bright Is That Star? Section 1 Stars How Bright Is That Star? The apparent magnitude is the brightness of a star as seen from Earth. The absolute magnitude is the brightness that a star would have at a distance of 32.6 light-years from Earth. If all stars were the same distance away, their absolute magnitudes would be the same as their apparent magnitudes.

Absolute and Apparent Magnitude Chapter 15 Stars, Galaxies, and the Universe Absolute and Apparent Magnitude

Chapter 15 Distance to the Stars Section 1 Stars Distance to the Stars Because stars are so far away, astronomers use a unit called a light-year to measure the distance from Earth to the stars. A light-year is the distance that light travels in one year, about 9.46 trillion kilometers.

Chapter 15 Motions of Stars Section 1 Stars Motions of Stars This apparent motion of the stars is due to Earth’s rotation and its revolution around the sun. Each star is actually moving in space. But because stars are so distant, their actual motion is hard to see.

Chapter 15 Bellringer List 3 stages in the life cycle of an insect. Section 2 The Life Cycle of Stars Bellringer List 3 stages in the life cycle of an insect. List 3 stages in the life cycle of a human. List any stages you may know of in the life cycle of a star. Write your answers in your Science Journal.

Chapter 15 What You Will Learn Section 2 The Life Cycle of Stars What You Will Learn During star formation, gravity pulls dust and gas into a sphere, and when the sphere gets dense enough, nuclear fusion begins. Nuclear Fusion is an atomic reaction that fuels stars.

Chapter 15 Section 2 The Life Cycle of Stars Types of Stars Stars can be classified by mass, size, brightness, color, temperature, composition, and age. A star is classified differently as its properties change. Its properties often relate to whether the star can generate energy by nuclear fusion.

The Life Cycle of Sunlike Stars Chapter 15 Section 2 The Life Cycle of Stars The Life Cycle of Sunlike Stars New stars form from gas and dust, which are pulled into a sphere by gravity. As the sphere becomes denser, hydrogen combines into helium and energy is released in a process called nuclear fusion.

Chapter 15 Bellringer What do you think galaxies are made of? Section 3 Galaxies Bellringer What do you think galaxies are made of? What is the name of the galaxy in which we live? Draw a sketch of what you think a spiral galaxy looks like when viewed from outside that galaxy. Record your answers in your Science Journal.

Chapter 15 What You Will Learn Section 3 Galaxies What You Will Learn The three types of galaxies are spiral galaxies, elliptical galaxies, and irregular galaxies. Galaxies are composed of stars, planetary systems, nebulas, and star clusters. Looking at distant galaxies reveals what young galaxies looked like.

Chapter 15 Types of Galaxies Section 3 Galaxies Types of Galaxies A galaxy is a collection of stars, dust, and gas bound together by gravity. Astronomers classify a galaxy as spiral, elliptical, or irregular according to its shape and rate of star formation.

Types of Galaxies, continued Chapter 15 Section 3 Galaxies Types of Galaxies, continued Spiral galaxies have a bulge at the center and spiral arms. The spiral arms are made of gas, dust, and new stars that have formed. The galaxy in which we live is a spiral galaxy called the Milky Way.

Types of Galaxies, continued Chapter 15 Section 3 Galaxies Types of Galaxies, continued Most elliptical galaxies are round or oval and seem to have stopped making new stars. Elliptical galaxies are among the largest galaxies in the universe. Irregular galaxies have no definite shape and form new stars slowly.

Chapter 15 Contents of Galaxies Section 3 Galaxies Contents of Galaxies Some galaxies contain nebulas and star clusters. A nebula is a large cloud of gas and dust in interstellar space. Nebulas are a region in space where stars are born.

Contents of Galaxies, continued Chapter 15 Section 3 Galaxies Contents of Galaxies, continued A globular cluster is a highly concentrated group of up to 1 million stars that looks like a ball. Open clusters are groups of 100 to 1,000 stars that are close together relative to other stars.

Chapter 15 Stars, Galaxies, and the Universe Contents of Galaxies

Gravity and the Universe Section 4 Formation of the Universe Chapter 15 Gravity and the Universe Gravitational attraction caused the matter distributed throughout the universe to form galaxies. Because gravity acts over such great distances, gravity controls the size and shape of the universe. Every object in the universe is part of a larger system and gravity acts within each system.

Structure of the Universe Chapter 15 Stars, Galaxies, and the Universe Structure of the Universe