chapter 5: earth and its moon. goals compare the earth and the moon and explain differences describe...

Chapter 5: Earth and Its Moon


Goals

• Compare the Earth and the Moon and explain differences

• Describe the effects of gravity between the Earth and Moon

• Explain the greenhouse effect

• Discuss theories of formation and evolution of Earth and Moon


Mass=1.0Density=5500 kg/m3

Gravity=1.0Escape Velocity=11.2 km/sRotation period=23h 56m

Mass=0.012Density=3300 kg/m3

Gravity=0.17Escape Velocity=2.4 km/sRotation period=27.3 days

Moon is in synchronous rotation


Tides

The gravitation attraction between the Earth and the Moon causes a tidal force resulting in deformations of the solid surfaces of both and the oceans of the Earth.

Since the oceans are liquid they can respond more.

As the Earth rotates under the tidal bulge the surface experiences two high and low tides each day.


The Sun produces about half as much tidal force on the Earth as does the Moon.

When they are aligned (New and Full Moon) the effects add. (spring tides)

When they are perpendicular to each other (1st and 3rd quarters) their effects tend to cancel. (neap tides)

What time of the month should we go to the beach?

Because it takes energy to make tides, the two bodies tend to lock their rotation and revolution rates.


Tides are most pronounced when you are up close to a large (strong gravity) object (like a black hole).

Therefor the tides the Earth imposes on the Moon are stronger than the tides the Moon imposes on the Earth

Because of this the Moon has been locked in rotation long before the Earth will.

The ultimate outcome of the tides is that the Earth and Moon will both be locked and one rotation of the Earth will take 47 days and the Moon will be 550,000 miles distant.


The Earth has been blessed with a substantial atmosphereNitrogen 78 %Oxygen 21 %Argon 0.9 %Carbon Dioxide 0.03 %Water Vapor 0.1-3 %

The Moon has none and was permanently polluted by the visit of the Apollo astronauts.

The reason is that the Earth’s temperature and gravity are such that these molecules have average velocities less than the escape velocity of the Earth, while the Moon’s low gravity and high temperatures prevent it from holding onto these gases.

Escape velocity sqrt(mass of planet/radius of planet)molecular speed sqrt(temperature/mass of gas)


The greenhouse effect does not involve Ozone but CO2 and H2O.

The sun’s radiation makes it through the atmosphere and warms the ground.

While the Sun’s blackbody curve peaks in the visible (5000ko), the Earth’s blackbody curve peaks in the infrared where the gases are not transparent. Thus these gases hold in the heat from the earth.

Without these gases the Earth would be 40o cooler.


The Moon’s surface contains craters, mountains, and evidence of lava flow.

Due to its airless environment and lack of geologic activity the surface of the Moon has remained largely unchanged for billion of years.

There are two distinct regions: the highlands (terrae) , and the lowlands (maria).


Near side of Moon Far side of Moon


Sizes from 50 km to 500m


The Moon’s surface has been bombarded by meteors.

This has caused craters of all sizes.

Most of the bombardment occurred billions of years ago during the formation of the solar system.

Because of this the Moon’s surface is covered with dust 20m thick.

The highlands are much more heavenly cratered proving they are older.

The lowlands are the result of lava flooded plains

chapter 5: earth and its moon. goals compare the earth and the moon and explain differences describe...

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