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.