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

Unit 6 Lesson 2 What Are Moon Phases?

Copyright © Houghton Mifflin Harcourt Publishing Company




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.


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.


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.


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.”




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.

• 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.


Moon Phases



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.


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.


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.


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.


Moon Phases


• Different amounts of the moon’s lit side are seen from Earth as the moon goes through its 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.

• 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. Each month is based roughly on the moon’s phases.



• The Chinese zodiac calendar is based in part on the phases of the moon. Twelve animals stand for cycles of time on this calendar.

• 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.


Lunar and Solar Calendars

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