Lesson 1 The View from Earth Lesson 2 The Sun and Other Stars 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 Chapter Menu

What makes up the universe and how does gravity affect the universe? Chapter Introduction

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. Chapter Introduction

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. Chapter Introduction

Lesson 1 Reading Guide - KC 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? Lesson 1 Reading Guide - KC

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 Lesson 1-1

Present-day astronomers use many ancient constellations to divide the sky into 88 regions. Lesson 1-1

Dividing the sky helps scientists communicate to others what area of sky they are studying. Lesson 1-1

Looking at the Night Sky (cont.) How do astronomers divide the night sky? Lesson 1-1

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 Lesson 1-1

Looking at the Night Sky (cont.) The electromagnetic spectrum is a continuous range of wavelengths. Lesson 1-1

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. Lesson 1-1

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. Lesson 1-1

Looking at the Night Sky (cont.) What can astronomers learn from a star’s spectrum? Lesson 1-1

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” Lesson 1-2

The object is viewed from two extreme points in Earth’s orbit. 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. Lesson 1-2

An astronomical unit is the average distance between Earth and the Sun, about 150 million km. Lesson 1-2

Measuring Distances (cont.) A light-year is the distance light travels in 1 year. One light-year is about 10 trillion km. Lesson 1-2

Measuring Brightness The apparent magnitude of an object is a measure of how bright it appears from Earth. Lesson 1-3

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. Lesson 1-3

Measuring Brightness (cont.) How do scientists measure the brightness of stars? Lesson 1-3

Astronomers use ancient constellations to divide the sky into sections, also called constellations. Lesson 1 - VS

Different wavelengths of the electromagnetic spectrum carry different energies. Lesson 1 - VS

Astronomers measure distances within the solar system using astronomical units. Lesson 1 - VS

Which term refers to how bright an object appears from Earth? A. luminosity B. light-year C. apparent magnitude D. absolute magnitude Lesson 1 – LR1

One light-year is equal to about how many kilometers? A. one million B. ten million C. one trillion D. ten trillion Lesson 1 – LR2

Which term refers to the range of wavelengths a star emits? A. brightness B. luminosity C. magnitude D. spectrum Lesson 1 – LR3

1. The night sky is divided into constellations. Do you agree or disagree? 1. The night sky is divided into constellations. 2. A light-year is a measurement of time. Lesson 1 - Now

Lesson 2 Reading Guide - KC 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? Lesson 2 Reading Guide - KC

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. Lesson 2-1

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. Lesson 2-1

How Stars Shine (cont.) How do stars shine? Lesson 2-1

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 Lesson 2-2

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. Lesson 2-2

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. Lesson 2-2

Composition and Structure of Stars (cont.) What are the interior layers of a star? Lesson 2-2

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. Lesson 2-2

Composition and Structure of Stars (cont.) The photosphere is the apparent surface of a star, where light energy radiates into space. Lesson 2-2

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. Lesson 2-2

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 Lesson 2-2

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 Lesson 2-2

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 Lesson 2-2

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 Lesson 2-2

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. Lesson 2-3

Classifying Stars Scientists classify stars according to their spectra. Though there are exceptions, color in most stars is related to mass. Lesson 2-4

Blue-white stars tend to have the most mass, followed by white stars, yellow stars, orange stars, and red stars. Lesson 2-4

The Hertzsprung-Russell diagram is a graph that plots luminosity against temperature of stars. Lesson 2-4

The y-axis of the H-R diagram displays increasing luminosity and the x-axis displays decreasing temperature. Lesson 2-4

Most stars exist along the main sequence. Lesson 2-4

The mass of a main-sequence star determines both its temperature and its luminosity Lesson 2-4

Classifying Stars (cont.) What is the Hertzsprung-Russell diagram? Lesson 2-4

Hot gas moves up and cool gas moves down in the Sun’s convection zone. Lesson 2 - VS

Globular clusters contain hundreds of thousands of stars. Sunspots are relatively dark areas on the Sun that have strong magnetic activity. Globular clusters contain hundreds of thousands of stars. Lesson 2 - VS

Which term refers to the wide, outermost layer of a star’s atmosphere? A. radiative zone B. corona C. convection zone D. chromosphere Lesson 2 – LR1

Scientists classify stars according to which of these? A. mass B. size C. spectra D. temperature Lesson 2 – LR2

What color of stars tend to have the most mass? A. yellow B. red C. orange D. blue-white Lesson 2 – LR3

3. Stars shine because there are nuclear reactions in their cores. 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. Lesson 2 - Now

Lesson 3 Reading Guide - KC Evolution of Stars How do stars form? How does a star’s mass affect its evolution? How is star matter recycled in space? Lesson 3 Reading Guide - KC

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” Lesson 3-1