Earth’s Moon and Lunar Phases

Moon Formation

Although the moon is the closest object in space to Earth and humans have been able to sample and study its surface, much is still unknown about the moon’s origins.  The most widely accepted idea is that while the planets in the solar system were forming, a collision occurred between a young Earth and another large solar system body.  Debris from this collision collected through the process of accretion in Earth’s orbit and gradually came together to form the moon.  This theory is known as the Impact Theory.

Lunar Geology

The moon is only about one-fourth the size of planet Earth, too small to hold onto an atmosphere.  Because of its lack of atmosphere, life does not exist on the moon, and neither do the geological processes of erosion and deposition.  Without these processes, the geology of the moon does not change, making it easier for astronomers to study the moon’s geological history from afar.  In fact, the footprints of Neil Armstrong, the first man to walk on the Moon, are still there! One of these footprints can be seen in the image to the left.

Gravity on the Noon is one-sixth of that on Earth’s surface. A 150-pound person would weigh only 25 pounds on the moon, because his or her mass does not change, only his or her weight. This allows astronauts to carry heavy equipment on their backs and allows them to breathe and work in an atmosphere-less environment.

Many areas of the Moon are both covered in a deep layer of debris known as lunar regolith.  This is the soil of the moon and is composed of igneous rocks and dust.  The regolith is about 3 meters (10 feet) thick.

The moon is made of two types of rock, light-colored Anorthosite and areas of dark basalt.  It also has several interesting geographic features. In this interactivity, click on the shaded sections of the Moon to learn more about its unique features. Click the player button to begin.

View a printable version of this interactivity.

 

 

Lunar Phases

Did you know that from Earth you can only ever see one half of the Moon?  You may have heard of the “dark side” of the Moon, and this refers to the side of the Moon that cannot be seen from Earth.  This is because the Moon rotates and revolves at the same speed, causing only one side of the Moon to be visible from Earth.  It was not until the Apollo 8 mission orbiting the Moon in 1968 that any human ever viewed the Moon’s “dark side."

The Sun is 93 million miles away from Earth, but it is so massive that its gravity is enough to keep Earth in orbit around it. The Moon is only about one-fourth the size of Earth, but it is close enough that its gravity affects conditions on Earth, too. Both the Sun and the Moon have an effect on Earth’s tidal cycles.  Though it is smaller, the proximity of the moon to Earth increases its tidal influences over the influence of the Sun.  The Sun’s tidal influence is slightly less than half the influence of the Moon.  Tidal cycles on Earth align with the phases of the moon as the moon revolves around the Earth.

From Earth, the Moon seems to light up the night sky, especially in its full-moon phase. In reality, the Moon does not emit light. It is the Sun's rays reflecting off the Moon's surface that illuminates it. The Moon orbits the Earth as the Earth revolves around the Sun. As the Moon changes its position in its orbit, and the Earth changes its position in relation to the Sun, people are able to see changes in the Moon's appearance from the viewpoint on Earth. The daily change in the Moon's appearance is due to lunar phases. In this interactivity, learn more about each phase and associated tidal influences by clicking on the icon next to each moon phase. Click the player button to begin.

View a printable version of the interactivity.

The Moon’s appearance seems to change because of its phases. Visit the Dial-A-Moon website at NASA. Enter your birthday to find the Moon phase for the night of your birthday for 2013.  Next, visit the Dial-A-Moon website for 2012, and enter your birthday to see what Moon phase appeared on the date of your birth for 2012.  How do your two Moons compare to each other?

 

Earth’s Moon and Lunar Phases Review

Now that you have explored the formation, geology, and lunar phases of the Moon, review your knowledge in this non-graded activity. Read the directions provided with each question. Then, click SUBMIT to check your responses. Click the player button to get started.