THE MOON

Birth of the Moon Moon is 4.5 billion years old. Late in formation of the Earth, Earth collided with a large planetesimal. Impact ejected millions of tons of debris It cooled and gravity drew it in to form the moon. Thick, solid crust. Mantle which is low in iron core

Features of the Moon One quarter the diameter of the earth barren ball of rock with no air or water No atmosphere because there was no volcanic activity because it was too cool. Its small mass is too weak a gravitational force to retain gases.

Craters have raised rims. They range in size from cms to 240 km. Large craters have mountain peaks in middle. Named for famous scientist. Maria are large smooth dark areas. Referred to as “seas”. Early observers thought they looked like oceans. They have poetic names. Ex: Mare Tranquillitatis is the site of the first lunar landing.

Highlands are bright area surrounding maria Made of different type of rocks that are less dense and older that mare rocks. Many have craters that overlap. Rays are light streaks of pulverized rock that radiate from craters. They are carved by ancient lava flow.

                                                                                                                                                                                                                                                

Same side of moon faces the sun. orbit is elliptical with a period of 27.3 days. Synchronous rotation means the rotation period equal to the orbital period. This is caused by the earth’s gravity. The orbit is tilted 5o with respect to Earth’s orbit. This is because of the odd mass ratio of moon to earth. (1/80)

It is the reason we see only one face of the moon.

Tides Regular change in the height of the ocean is caused by the moon. Moon exerts a gravitational attraction on the Earth. Attraction is stronger on side of Earth near the moon. It is weaker on side away from moon. The difference is called differential gravitational force which causes a tidal bulge.

There are 2 high tides and 2 low tides a day because as Earth rotates it carries points along the coast through tidal bulges.

Sun also causes tides for the same reason but it has less effect because it is much farther away. Spring tides occur when sun and moon work together. It occurs at full moon and new moon. Neap tide occurs when sun and moon are at 90o angle to each other. It occurs at 1st and 3rd quarter.

Tidal Braking Tides create forces on Earth and moon that slow their rotation. As Earth’s rotation slows, the Moon accelerates in its orbit moving farther from the Earth so to conserve angular momentum. Moon moves away about 3 cm a year. Earth slows by about .002 second.

Retrograde Motion