Earth-Moon System

Section 25.2

Earth’s Moon• The moon is about 384,000

kilometers away from the Earth

• Moon’s gravity is too weak to hold onto gas molecules, so there is no atmosphere and that causes the moon’s surface temperature to vary tremendously.

Earth’s Moon (cont.)

• No atmosphere means that there is no liquid water.

• If there were to be water then it would be frozen.

Surface Features• Major surface features of

the moon are maria, highlands, and craters.

• Maria and Highlands-• Maria- Low, flat plains

formed by ancient lunar lava flows.

• Highlands- Rough, mountainous regions

Surface Features (cont.)• Craters- Round depressions in

the surface caused by the impact of high-speed meteoroids.

• Meteoroids- Chunks of rock that move through the solar system.

“Notice how there are no craters visible on Earth compared to the moon?”

Formation of the Moon• Scientists hypothesize that the

moon formed after an enormous collision early in Earth’s history.

• 4.6 billions of years ago, the solar system was full of pieces of rocky debris, and this debris frequently collided with small planets.

• Material orbited Earth until it came together to form the moon.

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Interest Grabber Section 25.2

Shadow DanceHave you ever see an eclipse? This activity shows you why you don’t see an eclipse every month.

Darken the classroom. One student in eachgroup shines a flashlight (the sun) toward the wall from 1 m away. Another student holds a basketball (representing Earth) about 30 cm in front of the wall. A third student makes the tennis ball (the moon) orbit horizontally around the basketball. Observe what happens when the moon enters Earth’s shadow. Then change the moon’s orbit so it is not horizontal.

1. What happened when the moon entered Earth’s shadow?

2. When the moon’s orbit was horizontal, how often did the moon

enter Earth’s shadow?

3. When the moon’s orbit was tilted, how did this affect how often it

entered Earth’s shadow?

Phases of the Moon• Phases of the moon are

caused by changes in the positions of the moon, sun, and Earth.

• It takes 29.5 days for the moon to complete a full cycle of phases. This is known as a lunar month.

Phases of the Moon (cont.)

•Same side of the moon faces Earth.

•Moon makes one full rotation around its axis while making one full rotation around Earth.

Eclipses

• Occurs when the shadow of one body in space (planet or moon) falls on another.

• Sun, moon, and Earth must all lie along a straight line

Solar Eclipse• When the moon casts a

shadow on a portion of Earth’s surface.

• Umbra- Darkest part of the moon’s shadow

• Penumbra- Region of shadow that is less dark than the umbra.

Lunar Eclipse

• Occurs when the Earth casts a shadow on the moon.

• Unlike a solar eclipse, you can see a lunar eclipse anywhere on Earth that the moon is visible.

Tides on Earth• Tides are caused by differences in

the moon’s gravitational pull on Earth.

• The sun has a gravitational effect on the oceans, but its tidal effects are only about half those of the moon.

• Combined forces produce a spring tide, where changes between daily high and low tides are greatest.