Section Objectives• Identify what makes up the solar

system. • Describe how Earth moves in space. • Explain why Earth’s seasons change.

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.

The Earth in Space

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.

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.

The Earth in Space

• This revolution takes 365¼ days, which accounts for our need for a leap year once every four years.

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.

The Earth in Space

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The Earth in Space1

The Solar System

The Sun and the Seasons• Earth is tilted 23½ degrees on its axis.

• The day in which the Northern Hemisphere receives the most amount of sunlight is the summer solstice.

• Because of this, we have seasons as Earth rotates around the sun.

• On this day, the sun is directly over the Tropic of Cancer.

The Earth in Space1

The Sun and the Seasons (cont.)

• 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.

The Earth in Space

• 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.

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.

The Earth in Space1

The Earth in Space1

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Seasons

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.

The Earth in Space1

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Recalling Facts (cont.)

Science List two gases in the atmosphere.

nitrogen and oxygen

The Earth in Space1

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Recalling Facts (cont.)

Movement Which two motions does Earth make in space?

The Earth rotates on its axis and revolves around the sun.

The Earth in Space1

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