CHAPTER 1.4 –
EARTH’S MOON
IMPORTANT FACTS
• The first person to truly see the surface of the Moon was
Galileo in 1609.
• Galileo used a compound telescope which is a tube with
two lenses on either end. The lens brings in light and
helps magnify images.
 When Galileo used the compound telescope to see the
Moon, he found it to be an irregular surface with very
distinct land features. (The Greeks thought that the
Moon’s surface was perfectly smooth.)
Galileo and his compound
telescope
Galileo’s Drawings of the Moon
I. THE MOON’S SURFACE
• The features of the Moon’s surface include
maria, craters, and highlands.
A. MARIA
• The Moon has dark, flat areas. These
areas are hardened rock formed from
huge lava flows that occurred 3 – 4 billions
years ago.
• Galileo thought these dark, flat areas were
actual oceans on the Moon. The word
‘maria’ is Latin for ‘seas’.
The Moon’s Marias
B. CRATERS
• Galileo saw that the
Moon’s surface was
marked by large pits
called craters.
• The craters were
formed by the hard
impact of meteoroids
from space.
Meteoroids are
chunks of rock or dust
from space.
• Some of the craters on the Moon are hundreds
of kilometers wide.
• Early scientists mistakenly believed that the
craters were formed from volcanoes.
• The early Earth had a very similar crater surface
but it has been worn away by wind, water, and
time.
• The Moon does not have wind or water so the
surface has changed very little for billions of
years.
C. HIGHLANDS
• Galileo realized that the light areas of the
Moon must be some sort of a highland or
mountain.
• The sun’s light reflects of Moon’s
mountains ranges, highlands, and rims of
craters.
II. CHARACTERISTICS OF THE
MOON
 The Moon is dry, airless, small, and has a
wide variety of temperatures depending
upon which surface you are on.
A. SIZE AND DENSITY
• The Moon is 3,476 kilometers in diameter. The
Moon’s diameter is a little less that the width of
the entire U.S. (This is about ¼ of the Earth’s
diameter.)
• The Moon only has 1/80 the mass of Earth.
• Earth has a very dense, molten core and less
dense outer layers.
• The Moon’s mass is similar to the Earth’s outer
layers.
B. TEMPERATURE AND
ATMOSPHERE
• The Moon has no atmosphere.
• As a result, the temperatures vary wildly on the
Moon. In direct sunlight, the temperature is 130
degrees Celsius (266 degrees Fahrenheit). At
night, the temperature drops to -180 degrees
Celsius (-292 degrees Fahrenheit).
• The Moon’s surface gravity is very weak. This
allows gases found the Moon to easily escape
into space.
C. WATER
 The Moon has no liquid water.
 However, there is evidence that there may
be large ice patches near the Moon’s
poles.
III. THE ORIGIN OF THE MOON
• The origin of the Moon is a theory called
the collision-ring theory.
• About 4.5 billion years ago, the Earth was
a very young planet and the solar system
was full of rocky debris. Some of this
debris was the size of small planets.
• One of these planet-size debris hit the
Earth. Material from the object and the
Earth’s outer crust layers was ejected from
the impact into the orbit around the Earth.
• Gravity caused all of this material to
combine to form the Moon.