Section Objectives

1. Section Objectives • Identify what makes up the solar system.  • Describe how Earth moves in space.  • Explain why Earth’s seasons change.

2. The Earth in Space The Solar System • The solar system is made up of the sun, Earth, eight other planets, and thousands of smaller bodies (moons, comets, and asteroids).  • The planets and smaller bodies revolve around the sun.  • A planet follows an elliptical path around the sun. • This is known as its orbit.

3. The Solar System (cont.) • There are two types of planets—those solid and small like Earth, and those that resemble balls of gas like Jupiter.  • Earth is surrounded by a layer of air called the atmosphere. • Nitrogen and oxygen make up about 99 percent of this layer.  • Earth makes two motions in space.

4. The Earth in Space The Solar System (cont.) • It spins on an imaginary line (axis) that runs through the center of Earth between the North and South Poles.  • It takes 24 hours for Earth to complete one spin on this axis.  • The other motion is its complete orbit around the sun, or revolution.  • This revolution takes 365¼ days, which accounts for our need for a leapyear once every four years.

5. The Earth in Space How does Earth’s axis affect you? As Earth turns on its axis, different parts of the world are in sunlight or darkness, creating day and night. The tilt of the axis is responsible for the four seasons on Earth.

6. The Earth in Space 1 The Solar System Click the speaker button to play the audio.

7. The Earth in Space 1 The Sun and the Seasons • Earth is tilted 23½ degrees on its axis.  • Because of this, we have seasons as Earth rotates around the sun.  • The day in which the Northern Hemisphere receives the most amount of sunlight is the summer solstice. • On this day, the sun is directly over the Tropic of Cancer.

8. The Earth in Space The Sun and the Seasons (cont.) • The day in which the Northern Hemisphere receives the least amount of sunlight is the winter solstice. • On this day, the sun is directly over the Tropic of Capricorn.  • The two days each year in which the sun is directly over the Equator are known as the equinoxes. • Both hemispheres receive the same amount of sunlight on these days.

9. The Earth in Space 1 When is the first day of summer in the Northern Hemisphere? Explain what happens on this day. June 21 or 22 is the first day of summer. On noon of this day, the sun appears directly overhead at the line of latitude called the Tropic of Cancer [23½°N latitude]. This is the day with the most hours of sunlight in the Northern Hemisphere.

10. The Earth in Space 1 Seasons Click the speaker button to play the audio.

11. The Earth in Space 1 Recalling Facts Region Which bodies make up the solar system? The sun, Earth, eight other planets, and thousands of smaller bodies including Earth’s moon make up the solar system. Click the mouse button or press the Space Bar to display the answer.

12. The Earth in Space 1 Recalling Facts (cont.) Science List two gases in the atmosphere. nitrogen and oxygen Click the mouse button or press the Space Bar to display the answer.

13. The Earth in Space 1 Recalling Facts (cont.) Movement Which two motions does Earth make in space? The Earth rotates on its axis and revolves around the sun. Click the mouse button or press the Space Bar to display the answer.