Chapter Menu Chapter Introduction Lesson 1Lesson 1The Structure of the Solar System Lesson 2Lesson 2The Inner Planets Lesson 3Lesson 3The Outer Planets Lesson 4Lesson 4Dwarf Planets and Other Objects Chapter Wrap-Up NASA/JPL/USGS

Chapter Introduction 1.Astronomers measure distances between space objects using astronomical units. 2.Gravitational force keeps planets in orbit around the Sun. 3.Earth is the only inner planet that has a moon. Do you agree or disagree?

Chapter Introduction 4.Venus is the hottest planet in the solar system. 5.The outer planets also are called the gas giants. 6.The atmospheres of Saturn and Jupiter are mainly water vapor. Do you agree or disagree?

Chapter Introduction 7.Asteroids and comets are mainly rock and ice. 8.A meteoroid is a meteor that strikes Earth. Do you agree or disagree?

Lesson 1 Reading Guide - KC How are the inner planets different from the outer planets? What is an astronomical unit and why is it used? What is the shape of a planet’s orbit? The Structure of the Solar System

Lesson 1-1 Almost all of the specks of light you can see in the night sky are stars. A few of the tiny lights are part of our solar system. Stars are much farther away than objects in our solar system. What is the solar system?

Lesson 1-2 The largest object in the solar system is the Sun, a star. Objects in the Solar System star Science Use an object in space made of gases in which nuclear fusion reactions occur that emit energy Common Use a shape that usually has five or six points around a common center

Lesson 1-2 Planets orbit the Sun and have nearly spherical shapes. The mass of a planet must be much larger than the total mass of all other objects whose orbits are close by. Objects in the Solar System (cont.)

Lesson 1-2 Eight of the objects in the solar system are planets. Objects in the Solar System (cont.) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Lesson 1-2 Mercury, Venus, Earth, and Mars are the inner planets. The inner planets are mostly solid, rocky material.

Lesson 1-2 Jupiter, Saturn, Uranus, and Neptune are the outer planets. The outer planets are mostly ice and gases, such as hydrogen and helium.

Lesson 1-2 A dwarf planet is a spherical object that orbits the Sun and is not a moon or another planet. Dwarf planets are in regions of the solar system where there are many objects orbiting nearby. Objects in the Solar System (cont.)

Lesson 1-2 Ceres, a dwarf planet, orbits the Sun as planets do.

Lesson 1-2 Millions of small, rocky objects called asteroids orbit the Sun in the asteroid belt between the orbits of Mars and Jupiter. asteroids Asteroids vary in size and are usually not spherical. A comet is made of gas, dust, and ice and moves around the Sun in an oval- shaped orbit.comet Objects in the Solar System (cont.)

Lesson 1-2 Distances between objects in the solar system are extremely large. Astronomers do not use meters or kilometers to describe these distances. A more convenient unit is used— the astronomical unit (AU).astronomical unit One AU is Earth’s average distance from the Sun—about 150,000,000 km. Objects in the Solar System (cont.)

Lesson 1-2 It is easier to express very large distances using astronomical units rather than kilometers.

Lesson 1-3 The time it takes an object to travel once around the Sun is its period of revolution.period of revolution The time it takes an object to complete one rotation is its period of rotation.period of rotation The Motion of the Planets

Lesson 1-3 A planet’s orbit is an ellipse— a stretched-out circle. Focus points, or foci, determine the shape of the ellipse. The Motion of the Planets (cont.)

Lesson 1 - VS The solar system contains the Sun, the inner planets, the outer planets, the dwarf planets, asteroids, and comets.

Lesson 1 - VS An astronomical unit (AU) is a unit of distance equal to about 150 million km.

Lesson 1 - VS The speeds of the planets change as they move around the Sun in elliptical orbits.

Lesson 1 – LR1 A.asteroids B.comets C.planets D.stars What are most of the specks that you can see in the night sky?

Lesson 1 – LR2 A.asteroid B.astronomical unit C.comet D.dwarf planet What is a spherical object that orbits the Sun and is not a moon or another planet?

Lesson 1 – LR3 A.astronomical unit B.focus C.period of revolution D.period of rotation Which refers to the time it takes an object to complete one rotation?

Lesson 1 - Now 1.Astronomers measure distances between space objects using astronomical units. 2.Gravitational force keeps planets in orbit around the Sun. Do you agree or disagree?