Learning Objectives

• Describe the Moon's features and its special relationship with our planet Earth.

• Explain why we always see the same side of the Moon and its phases.

• Identify the major features of the Moon's surface like craters, maria, and terrae.

• Summarize the most accepted scientific theory about how the Moon was formed.

• Explain the main difference between a solar eclipse and a lunar eclipse.

Key Vocabulary

Satellite

An object that orbits a larger object in space, like the Moon orbiting the Earth.

Synchronous Rotation

This is when an object's rotation period matches its orbital period around another body.

Craters

Bowl-shaped basins on a celestial body's surface that are caused by meteorite impacts.

Maria

These are the dark, solid, and flat areas of cooled lava on the Moon's surface.

Terrae

These are the light-colored, mountainous highland regions of the lunar surface.

Eclipse

An event where one celestial body blocks light from or casts a shadow on another.

Earth's Moon & Its Orbit

• The Moon is Earth's natural satellite and reflects the Sun's light.

• Its rotation and orbit around Earth both take 27.3 days.

• This is why we always see the same side of the Moon.

Phases, Atmosphere, and Temperature

Moon's Phases

• The phases of the Moon show our changing view of its sunlit half from Earth.

• A complete cycle of phases, from one new moon to the next, takes about 29.5 days.

• Waxing phases are when the lit-up part grows, while waning phases are when it shrinks.

Atmosphere & Temperature

• The Moon has a very thin exosphere, which does not protect it like an atmosphere.

• Without protection, daytime temperatures can soar to a very hot 123°C (253°F).

• At night, the surface temperature can plunge to an extremely cold -233°C (-397°F).

The Lunar Surface: Maria and Terrae

Maria (Dark Areas)

• ​These are large, dark, flat plains created by ancient lava flows made of basalt rock.

• ​​They were formed when lava filled large craters between 3 to 4 billion years ago.

• ​Maria cover about 16% of the Moon's surface, mostly on the side that faces the Earth.

Terrae (Light Areas)

• ​These are light-colored areas, also known as highlands, that have a higher elevation than the maria.

• ​​They include mountain ranges and are made of a lighter-colored rock called feldspar.

• ​The highlands are older than the maria and are part of the Moon's original crust.

Craters and Water on the Moon

• Craters are bowl-shaped basins on the Moon from meteoroid impacts.

• ​They don't change because the Moon has no wind or weather.

• Scientists have found water molecules mixed into the lunar soil.

• Water ice is also found in very cold, permanently shadowed craters.

Lunar Interior and Formation

Inside the Moon

• ​Like Earth, the Moon has three main layers: a crust, a mantle, and a core.

• ​​Its rocky mantle is made of minerals like olivine, and the crust is thicker on the far side.

• ​The Moon has a small, metallic core that is made up of mostly iron.

How the Moon Formed

• ​The Giant Impact Theory is the most accepted idea about the Moon's origin.

• ​​A huge object, about the size of Mars, crashed into a young Earth 4.5 billion years ago.

• ​Debris from this impact eventually clumped together in orbit to form the Moon.

Eclipses

Solar Eclipse

• ​A solar eclipse occurs when the Moon passes directly between the Sun and Earth.

• ​​The Moon’s shadow is cast on a part of the Earth, blocking the Sun.

• ​This alignment makes it look like the Sun has temporarily disappeared from view.

Lunar Eclipse

• ​A lunar eclipse happens when Earth is directly between the Sun and the Moon.

• ​​During this alignment, Earth’s much larger shadow is cast upon the Moon.

• ​This makes the Moon appear dim and it can sometimes turn a reddish color.

Common Misconceptions About the Moon

Summary

• The Moon is Earth's natural satellite and is held in orbit by gravity.

• The lack of an atmosphere on the Moon causes extreme surface temperatures.

• The Moon's surface has dark maria, light terrae, and many impact craters.

• Like Earth, the Moon is made up of a crust, mantle, and core.

• The Giant Impact Theory explains how the Moon was most likely formed.

• Eclipses occur when the Sun, Earth, and Moon are in alignment.