1. The Moon
28.2

2. Reaching for the Moon
Much of our knowledge of the Moon comes from explorations by space probes and astronauts.
The first step was taken in 1957 with the launch of the first satellite, Sputnik I, by the Soviet Union.

3. Reaching for the Moon
In 1961, Soviet cosmonaut Yuri Gagarin became the first human in space.
The United States’ Project Mercury launched the first American, Alan Shepard Jr., into space on May 5, 1961.

4. Reaching for the Moon
Project Gemini launched two-person crews into space, and on July 20, 1969, the Apollo program landed Neil Armstrong and Buzz Aldrin on the Moon, during Apollo 11.

5. Lunar Properties
The Moon’s radius is about 27% of Earth’s radius, and its mass is more than 1% of Earth’s mass.
Most moons are much smaller than this.
The Moons orbit is relatively farther from Earth than most moons are from the planets they orbit.

6. Lunar Surface
The albedo of the Moon, the amount of sunlight that its surface reflects, is very small (7%).
The sunlight that is absorbed by the surface of the Moon is responsible for the extreme differences in temperatures on its surface.
127°C to -173°C

7. The Lunar Surface There is no erosion on the Moon except for impacts.
The surface of the Moon consists of several features.
Regions called highlands are light in color, mountainous, and heavily covered with craters.

8. The Lunar Surface Regions called maria (mare) are dark, smooth plains.
All of the craters on the Moon are impact craters, formed when objects from space crashed into the lunar surface.
The material blasted out during these impacts fell back to the surface as ejecta.

9. The Lunar Surface
Some craters have long trails of ejecta, called rays, that radiate outward.
Rilles are meandering, valleylike structures.

11. Composition
The Moon is covered in minerals similar to those of Earth, mostly silicates.

12. History of the Moon The Moon is between 3.8 and 4.6 billion years old.
During its first 800 million years the Moon was heavily bombarded which resulted into forming a layer of loose, ground-up rock, called regolith on the surface of the Moon.

13. History of the Moon
After the bombardment, lava welled up from the Moon’s interior and filled in the large impact basins to form maria.
The Moon is twice as thick on the far side of the moon.

14. Tectonics on the Moon?
Scientists infer from seismometer data that the Moon, like Earth, has a layered structure, which consists of the crust, the upper mantle, the lower mantle, and the core.
The Moon experiences a moonquake once a year, but scientists theorize that the Moon is not tectonically active.

15. Formation Theories
The capture theory proposes that as the solar system was forming, a large object ventured too near to the forming Earth, became trapped in its gravitational pull, and formed into what is now the Moon.
The problem with that is that something would have to slow it down, and the moon and earth would have difference compositions.

16. Formation Theories
Another theory, called the simultaneous formation theory says the Moon and Earth formed at the same time and in the same general area which makes the materials the same.
This theory does not account for the different amounts of iron on Earth and on the Moon.

17. Formation Theories
The most commonly accepted theory of how the Moon formed, the impact theory.
The Moon formed as the result of a gigantic collision between Earth and a Mars-sized object about 4.5 billion years ago, when the solar system was forming.

18. Formation Theories
As a result of the collision, materials from the incoming body and from Earth’s outer layers were ejected into space, where they merged together to form the Moon.