1. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 1

2. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 2

3. Unit 6 Lesson 2 What Are Moon Phases?
Our Moon
The moon is Earth’s satellite. A satellite is an object that moves around another larger object in space.
The moon is the largest, brightest object in the night sky. It looks large, because it is so close to Earth.
Copyright © Houghton Mifflin Harcourt Publishing Company 3

4. Unit 6 Lesson 2 What Are Moon Phases?
Our Moon
However, the moon is small compared to Earth. It is about one-fourth the size of Earth. The moon has no air, wind, or liquid water.
Copyright © Houghton Mifflin Harcourt Publishing Company 4

5. Unit 6 Lesson 2 What Are Moon Phases?
Our Moon
We see the moon because light from the sun reflects from it and back to Earth.
The pull of Earth’s gravity keeps the moon in orbit around Earth.
Only one side of the moon is seen from Earth, because the moon takes the same amount of time to rotate around its axis once as it does to orbit Earth once.
Copyright © Houghton Mifflin Harcourt Publishing Company 5

6. Unit 6 Lesson 2 What Are Moon Phases?
Our Moon
The moon’s surface has many craters (holes) on it. These craters were formed by rocks and chunks of debris slamming into the moon.
The surface of the moon has mountains and large, flat, plains (flat areas). The plains are called maria, a Latin word meaning “seas.”
Copyright © Houghton Mifflin Harcourt Publishing Company 6

7. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 7

8. Unit 6 Lesson 2 What Are Moon Phases?
The motions of Earth and the moon are responsible for the phases you see. As the moon revolves around Earth, the amount of the lit part that we see changes.
Copyright © Houghton Mifflin Harcourt Publishing Company 8

9. Unit 6 Lesson 2 What Are Moon Phases?
These different amounts of the moon’s lighted side are the different phases of the moon.
Each phase of the moon has a different shape.
It takes about one month for the moon to complete all of its phases. Then the cycle repeats.
Copyright © Houghton Mifflin Harcourt Publishing Company 9

10. Unit 6 Lesson 2 What Are Moon Phases?
As Earth orbits the sun, the moon also orbits Earth. The moon reflects light from the sun. As the moon travels in its orbit, different amounts of the moon’s lit side can be seen from Earth.
Copyright © Houghton Mifflin Harcourt Publishing Company 10

11. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 11

12. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 12

13. Moon Phases Unit 6 Lesson 2 What Are Moon Phases? 13
Copyright © Houghton Mifflin Harcourt Publishing Company 13

14. Unit 6 Lesson 2 What Are Moon Phases?
As Earth orbits the sun, the moon also orbits Earth. The moon reflects light from the sun. As the moon travels in its orbit, different amounts of the moon’s lit side can be seen from Earth.
Copyright © Houghton Mifflin Harcourt Publishing Company 14

15. Unit 6 Lesson 2 What Are Moon Phases?
The changes in the appearance of the moon’s shape are known as moon phases.
Even though sunlight reflects from the moon to Earth, the sun lights only half of the moon at any time.
Copyright © Houghton Mifflin Harcourt Publishing Company 15

16. Unit 6 Lesson 2 What Are Moon Phases?
We see a full moon when all of the lit part of the moon faces Earth. Then, we see less and less of the moon until we are at the new moon again.
Copyright © Houghton Mifflin Harcourt Publishing Company 16

17. Unit 6 Lesson 2 What Are Moon Phases?
During the new moon phase, we cannot see the moon, because the lit part faces away from Earth.
As the moon moves in its orbit around Earth, we see more of its lit part.
Copyright © Houghton Mifflin Harcourt Publishing Company 17

18. Moon Phases Unit 6 Lesson 2 What Are Moon Phases? 18
Copyright © Houghton Mifflin Harcourt Publishing Company 18

19. Unit 6 Lesson 2 What Are Moon Phases?
Different amounts of the moon’s lit side are seen from Earth as the moon goes through its phases.
Copyright © Houghton Mifflin Harcourt Publishing Company 19

20. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 20

21. Lunar and Solar Calendars
Unit 6 Lesson 2 What Are Moon Phases?
Lunar and Solar Calendars
For thousands of years, people used the phases of the moon to make calendars and to track time. These calendars are called lunar calendars.
Copyright © Houghton Mifflin Harcourt Publishing Company 21

22. Lunar and Solar Calendars
Unit 6 Lesson 2 What Are Moon Phases?
Lunar and Solar Calendars
Copyright © Houghton Mifflin Harcourt Publishing Company 22

23. Lunar and Solar Calendars
Unit 6 Lesson 2 What Are Moon Phases?
Lunar and Solar Calendars
Earth’s orbit around the sun has also been used to make calendars and track time. These calendars are called solar calendars.
Our modern calendar is based on Earth’s orbit around the sun.
Copyright © Houghton Mifflin Harcourt Publishing Company 23

24. Lunar and Solar Calendars
Unit 6 Lesson 2 What Are Moon Phases?
Lunar and Solar Calendars
The Chinese zodiac calendar is based in part on the phases of the moon. Twelve animals stand for cycles of time on this calendar.
Copyright © Houghton Mifflin Harcourt Publishing Company 24

25. Lunar and Solar Calendars
Unit 6 Lesson 2 What Are Moon Phases?
Lunar and Solar Calendars
The Aztec calendar is based on Earth’s orbit around the sun. Each part of this calendar is marked by animals or symbols, marking important times of year.
Copyright © Houghton Mifflin Harcourt Publishing Company 25

26. Unit 6 Lesson 2 What Are Moon Phases?
Copyright © Houghton Mifflin Harcourt Publishing Company 26