CHAPTER 1.4 – EARTH’S MOON

IMPORTANT FACTS The first person to truly see the surface of the Moon was Galileo in 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.