Chapter 6: The Moon

6.1 Description of the Moon

Text pp 188-193

Earth has only one natural

satellite – the moon.

Other planets have moons,

but our planet-satellite

system is unique in the

solar system because

Earth’s moon is unusually

large compared to its parent

planet.

(The diameter of the moon is

about one fourth that of

earth’s.)

General Features• The Moon possess no air, water, or life.

Lunar astronaut Buzz Aldrin called it a

place of “magnificent desolation.”

Fast Facts about the Moon

• The moon’s density is about 3.3 times that of water, while earth’s average density is about 5.5 times that of water. This difference might be because the moon’s iron core is proportionately small compared to earth’s.

• The gravity of the moon is 1/6th that of earth’s. (A 150-lb person weighs only 25 lbs on the moon.)

What the moon doesn’t have:

• Water and atmosphere.

• Weathering and erosion. (No wind or

water to wear the moon’s surface

down.)

• No tectonic forces (surface crust

movement), so no volcanic eruptions.

The Lunar SurfaceWhen Galileo first

looked at the moon

through a telescope,

he saw dark lowlands

and bright highlands.

Because the dark

regions resembled

earth’s seas, he called

them “maria,” the

Latin word for sea.

Since the moon is unprotected by an

atmosphere, the surface rocks are constantlybombarded by space particles and micro-

particles.

Moon rocks become slightly rounded on top from this,

and the landscape is

smoothed out a bit.

Even so, it’s

unlikely the moon

has changed very

much in the last 3

billion years,

except for a few

more craters.

Lunar Craters

• The most obvious features

of the lunar surface are

craters, which are round

depressions in the surface

of the moon.

• The moon even has craters

within craters!

Most craters were

produced by the impact

of rapidly moving debris.

The largest craters are

about the same size

as the state of Indiana.

Earth has only a few craters –

unlike the earth, the moon has

no atmosphere to burn up small

debris as it approaches, nor

wind or water to erode craters

over time.

• Craters usually have a raised

rim and range in size from

tiny holes less than a

centimeter across to gaping

scars such as Clavius, about

240 (150 km) across.

Some of the

larger

craters have

mountain

peaks at

their

centers.

Most lunar mountains are in fact rims of

craters, formed when astral debris

crashed into the moon’s surface.

These are milk drops taken with high speed

photography. How are they similar to lunar craters

in shape and formation?

This crater, Tycho, can be seen with your naked eye

during the fuller lunar phases, especially on a clear

night.

Maria• A mare is a dark,

smooth area on the

moon’s surface.

More than one mare

is called “maria.”

• Maria are ancient

beds of lava.

They originated when asteroids punctured the lunar surface, letting magma bleed out.

Lunar Highlands

• Lunar highlands are densely-pitted, light-

colored areas. These include crater-pitted

plains as well as mountain ranges

• The highest lunar peak is only one kilometer

lower than Mount Everest.

Rilles are

long channels

associated with

maria. They

look somewhat

like earth

valleys or

trenches.

(mare)

Rilles

Rilles can be straight, or

wind like a river on earth.They may be the

remnants of ancient

lava flows.

Rays

From many craters,

long, light streaks of

pulverized rock called

rays radiate outward, as

from the Tycho Crater.

RegolithAll lunar terrains are

covered with a layer

of grey debris called

“regolith.”

Regolith is made of bits of

igneous rock, glass beads

from asteroids crashing on

the lunar surface to form

craters, and fine lunar dust.The moon’s layer of

regolith averages about

3 meters thick.