1. ALSEP

• Apollo Lunar Surface Experiments Package

• Nuclear powered package of instruments left on Moon by Apollo astronauts to measure solar winds, measure lunar heat flow, and record seismic activity.

2. apogee

• point of greatest separation between Earth and Moon. Approximately 405,000 km.

3. Apollo Program

• U.S. space program to put men on the Moon. 12 men walked on the moon from July 1969 to December 1972.

4. crater

• circular depression on the Moon primarily caused by meteorites. (some caused by volcanic activity)

5. crater density

• average number of craters per unit of area. Much more concentrated in the highlands than in the maria (indicates the maria are younger).

6. ejecta blanket

• Material thrown out of a crater during its formation by meteoric impact.

7. erosion

• Wearing away of surface features. Caused on the Moon entirely by meteorite and micro-meteorite bombardment.

8. highlands

• Light-colored, higher-elevation areas on the Moon.

• Also called “terrae”.

9. impact breccia

• Many smaller rock fragments stuck together by the shock and heat of meteoric impact.

10. libration

• apparent rocking motion of the Moon caused by the fact that rotation speed is constant while orbital speed changes.

11. maria

• Dark-colored, lower-elevation areas on the Moon.

• Also called “lowlands”.

12. perigee

• Point of the Moon’s closest approach to the Earth. Approximately 363,000 km.

13. regolith

• Layer of pulverized ejecta. Lunar dust. Covers Moon to a depth of about 20 m.

• Regolith means “fine rocky layer”.

14. rille

• A ditch where molten lava once flowed.

15. synchronous orbit

• Orbit where rotational period equals orbital period. Causes the same side of the Moon to always face the Earth.

16. terrae

• The lunar highlands. (See number 8)

1. How far away is the Moon? How do we know?

• The Moon’s average distance is 384,000 km.

• This is determined by the time it takes a laser beam to be reflected back to the Earth.

2. Explain why, if the Moon always keeps a single face toward the Earth, we can see 59 percent of the lunar surface in a month.

• The Moon rotates at a constant speed, but its orbital speed varies throughout the ellipse. This causes more of each side to be visible at different times of the month.

3. Why does the Moon have no air?• The gravitational pull of the Moon is not

great enough to hold the gas molecules which would make

4. What is the primary source of erosion on the Moon? Why is the average rate of erosion on the Moon so much less than on Earth?

• The primary source of erosion on the Moon is meteoric and micro-meteoric bombardment.

• The Moon’s rate of erosion is slower than Earth’s because there is no running water or atmospheric wind.

5. Tell how lunar soil is different from earthly soil.

• No organic matter, fossils, or water.

6. What is a possible explanation for the lunar crust being thicker on the far side than on the near side?

• The Earth’s gravity pulled the denser lunar mantle slightly off-center compared to the less dense (and less gravitationally attracted) crust.

• This made the crust on the near side thinner than the crust on the far side.

7. Explain the four theories of the origin of the Moon. Which is favored by most of today’s astronomers? Why?

1. SISTER or Co-formation THEORY

• The moon formed as a separate object from the Earth from the same “blob” of material.

2. CAPTURE THEORY-

• The moon formed far from the Earth and was later captured by it.

3. DAUGHTER, or Fission THEORY-• The Moon came from the Earth itself as a

piece of the Earth was dislodged by rapid spinning.

4. IMPACT THEORY-

• A Mars-sized object collided with Earth in a glancing blow. This dislodged matter which then assembled into the Moon. (continued)

• The Impact theory is accepted by most astronomers because it has been shown to be the most probable in computer simulations.

8. Pretend you are an astronaut on the Moon. How would the Earth appear to change as you observed it for one month?

• The Earth would remain in one position in the sky and go through Moon-like phases over a 28 day period.

• Be sure you know the Moon’s size, mass, and density in comparison to the Earth’s.

• Be sure you know the size range of craters.