1. Table of Contents Earth in Space Gravity and Motion
Phases, Eclipses, and Tides
Earth’s Moon

2. How Earth Moves - Earth in Space
Earth moves through space in two major ways: rotation and revolution.

3. Sunlight Striking Earth’s Surface
- Earth in Space
Sunlight Striking Earth’s Surface
Near the equator, sunlight strikes Earth’s surface more directly and is less spread out than near the poles.

4. Seasons on Earth - Earth in Space
Earth has seasons because it is tilted as it revolves around the sun.

5. Seasons on Earth - Earth in Space
The height of the sun above the horizon varies with the season.

6. Seasons Activity - Earth in Space
Click the Active Art button to open a browser window and access Active Art about the seasons.

7. Using Prior Knowledge - Earth in Space
Before you read, write what you know about seasons on Earth in a graphic organizer like the one below. As you read, write what you learn.
What You Know
The sun’s rays heat Earth.
Earth has seasons.
In the Northern Hemisphere, fall begins in September and spring begins in March.
What You Learned
Areas where the sun hits Earth at a more direct angle are generally warmer than areas where the sun’s rays are more spread out.
The tilt of Earth’s axis as it moves around the sun causes seasons.
Around March 21 and September 22, day and night are each 12 hours long.

8. End of Section: Earth in Space

9. Gravity - Gravity and Motion
The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.

10. Gravity Versus Distance
- Gravity and Motion
Gravity Versus Distance
As a rocket leaves a planet’s surface, the force of gravity between the rocket and the planet changes. Use the graph to answer the following questions.

11. Gravity Versus Distance
- Gravity and Motion
Gravity Versus Distance
Reading Graphs:
What two variables are being graphed? In what units is each variable measured?
Force of gravity on the rocket in millions of newtons and distance from the planet’s center in planetary radii

12. Gravity Versus Distance
- Gravity and Motion
Gravity Versus Distance
Reading Graphs:
What is the force of gravity on the rocket at the planet’s surface?
Four million newtons

13. Gravity Versus Distance
- Gravity and Motion
Gravity Versus Distance
Reading Graphs:
What is the force of gravity on the rocket at a distance of two units (twice the planet’s radius from its center)?
One million newtons

14. Gravity Versus Distance
- Gravity and Motion
Gravity Versus Distance
Making Generalizations:
In general, how does the force of gravity pulling on the rocket change as the distance between it and the planet increases?
It decreases.

15. Gravity and Inertia - Gravity and Motion
Newton concluded that two factors–gravity and inertia–combine to keep the moon in orbit around Earth.

16. Asking Questions - Gravity and Motion
Before you read, preview the red headings. In a graphic organizer like the one below, ask a question for each heading. As you read, write answers to your questions.
Question
Answer
What is gravity?
Gravity is the force that attracts all objects toward one another.
What is inertia?
Inertia is the tendency of an object to resist a change in motion.

17. Click the SciLinks button for links on gravity.
- Gravity and Motion
Links on Gravity
Click the SciLinks button for links on gravity.

18. End of Section: Gravity and Motion

19. Motions of the Moon - Phases, Eclipses, and Tides
The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides.

20. Phases of the Moon - Phases, Eclipses, and Tides
The phase of moon you see depends on how much of the sunlit side of the moon faces Earth.

21. Moon Phases and Eclipses Activity
- Phases, Eclipses, and Tides
Moon Phases and Eclipses Activity
Click the Active Art button to open a browser window and access Active Art about moon phases and eclipses.

22. The Moon’s Orbit - Phases, Eclipses, and Tides
The moon’s orbit is tilted about 5 degrees relative to Earth’s orbit around the sun.

23. Solar Eclipse - Phases, Eclipses, and Tides
A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from parts of Earth.

24. Lunar Eclipse - Phases, Eclipses, and Tides
During a lunar eclipse, Earth blocks sunlight from reaching the moon.

25. Tides - Phases, Eclipses, and Tides
Tides occur mainly due to the difference in the force of gravity between the moon and different parts of Earth.

26. Spring and Neap Tides - Phases, Eclipses, and Tides
When Earth, the sun, and the moon are in a straight line, a spring tide occurs. When the moon is at a right angle to the sun, a neap tide occurs.

27. Previewing Visuals - Phases, Eclipses, and Tides
Preview Figure 11. Then write two questions you have about the diagram of the phases of the moon in a graphic organizer like the one below. As you read, answer your questions.
Earth’s History
Q. Why does the moon have phases?
A. The changing relative positions of the moon, Earth, and the sun cause the phases of the moon.
Q. Do we see different sides of the moon as the phases of the moon appear?
A. No; the same side of the moon always faces Earth.

28. End of Section: Phases, Eclipses, and Tides

29. The Moon’s Surface - Earth’s Moon
Features on the moon’s surface include maria, craters, and highlands.

30. The Moon’s Size - Earth’s Moon
The moon is 3,476 km in diameter, a little less than the distance across the contiguous Untied States.

31. The Origin of the Moon - Earth’s Moon
Scientists theorize that a planet-sized object collided with earth to form the moon.

32. Identifying Main Ideas
- Earth’s Moon
Identifying Main Ideas
As you read the section “The Moon’s Surface,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.
Main Idea
The moon’s surface has a variety of features such as…
Detail
Detail
Detail
Dark, flat areas called maria, which formed from huge lava flows
Large, round pits called craters, which were caused by the impact of meteoroids
Highlands, or mountains, which cover much of the moon’s surface

33. Click the SciLinks button for links on Earth’s moon.

34. End of Section: Earth’s Moon

35. Graphic Organizer Earth Around the sun On its axis Night and day Years
rotates
revolves
Around the sun
On its axis
causing
causing
Night and day
Years

36. End of Section: Graphic Organizer