The Moon

(It’s not made of green cheese!)

The Moon

The Moon is the brightest object in the night sky. It is one of the most beautiful and easiest things to see from Earth. You can see the Moon on most clear nights. Although the Moon seems to shine very brightly in the sky, it actually gives out no light of its own. The Moon reflects light that comes from the Sun.

Relative Size

The Moon The Earth

If the Moon was a tennis ball, and the Earth was a basket ball, the relative distance between the Earth and the Moon would be 7 meters, of half the length of a basketball court.

What is the Moon Made Of?

The Moon is mostly made up of rock. Like Earth, the Moon has three main layers. It has a stiff upper layer called a crust. The crust is at least 60 kilometers thick and is made of rock. Below the curst is a layer called the mantle. Most of the mantle is hard and rocky. The mantle surrounds a small core at the centre of the Moon. The core is made mostly of iron. The core measures about 680 kilometers across. It is mostly solid today, but it may have been molten and liquid billions of years ago when the Moon was hotter.

Patches on the Moon

Looking up at the Moon, you can see light and dark patches on its surface. Hundreds of years ago people thought the dark patches were seas, so they became known as maria, which is Latin for seas. They are not really seas but are low flat areas made of darker rocks. They were once filled with hot lava that flowed across the Moon billions of years ago.

The lighter patches on the Moon are rough and hilly. They are called highlands. The highlands have many craters which are bowl-shaped holes that were made when chunks of rock crashed into the Moon from space. Some large craters are hundreds of miles wide.

Does the Moon Move?

The Moon travels around Earth in an orbit. It takes the Moon 27 days to complete a lap around the Earth.

The Moon travels at a speed of 3,700 kilometers per hour.

The Moon rotates on its axis, but it does this in a special way so that the same side of the Moon always faces Earth. This is because the Moon spins on its axis in the same time that it takes to orbit the Earth. So in the 27 days the Moon travels around Earth once, it rotates on its own axis once.

The Dark Side of the Moon

The side of the Moon we cannot see from Earth is called the far side. Until spacecraft could reach the Moon, people did not know what the far side of the Moon looked like.

A Russian spacecraft called Luna 3 took the first pictures of the far side of the Moon in October 1959. It is much rougher and has many more craters than the side we always see from Earth.

The Phases of the Moon

The different shapes of the Moon that we see are called phases.

When the Moon is lined up between Earth and the Sun, the side of the Moon that faces us is not lit up at all by the Sun. This means that we cannot see the Moon at all, because it is too dark. This phase is called the new moon.

A few days later, we can see a thin curved shape called a crescent. The crescent slowly grows over the next few days. As the crescent gets larger it is called a waxing moon.

When the Moon has completed a quarter of its orbit around the Earth we see the first quarter - half of the Moon’s face is lit up by the Sun.

The Moon continues to wax and soon more than half the face is lit up. This shape is called gibbous, which means “hump shaped.”

Next, the full sunlit face of the Moon can be seen. This is the full moon phase. Earth is now lined up between the Sun and the Moon.

During the third quarter the Moon enters the second half of its orbit around the Earth. It grows thinner each night, this is called the waning moon. The Moon shrinks from a full moon to a gibbous moon again.

As the Moon complete its journey around Earth, it slowly because a waning crescent. Then the Moon is once again in the invisible new moon phase.

Animations

Moon Phase Animation: http://kids.msfc.nasa.gov/Earth/Moon/Moon.asp

Current Moon Phase: http://kids.msfc.nasa.gov/News/1999/News-Harvest

Moon.asp

Tides

The tides are a result of how Earth, the moon and the sun interact.

High Tide

The moon exerts a force on the Earth. Earth responds by moving toward the moon. Any water that is on the side of the Earth facing the moon moves faster than Earth can, this creates what is called an aqueous bulge. On the side of the Earth not facing the moon, Earth moves faster toward the moon than the water on that side. That creates another aqueous bulge. These larger bulges are what we call high tide.

As Earth rotates on its axis, the tides rise and fall as the seashores of the continents are pulled into and out of aqueous bulges.

The Sun’s Role in Tides

The sun also exerts a force on the Earth. If the moon and the sun were at the same distance from Earth, the sun’s force would be 180 times as strong as the moon’s. Since the moon is so much closer to Earth than the sun, the moon actually exerts more force – two times as great as the force of the sun.

The pull of the sun creates aqueous bulges too, but they are much smaller than the bulges created by the moon.

Spring and Neap Tides

The sun helps create what are called spring tides and neap tides.

With spring tides, the pull of the sun and the moon are in step. Either the moon and the sun are lined up directly (new moon phase), or they are on exact opposite sides of Earth (full moon phase). All that pulling makes for higher than normal tides.

Neap tides are lower than normal tides. They occur when the sun and the moon are out of step – when the pull of the sun and the pull of the moon are at right angles during the first and last quarter moons.

Eclipse

A lunar eclipse happens anytime the Moon enters Earth’s shadow. The Sun, the Moon and Earth have to be lined up exactly for a total eclipse to happen. For a lunar eclipse to happen, the Moon must be in the full moon phase and the Moon must pass through Earth’s shadow.

During a total eclipse of the Moon, Earth blocks the Sun’s light so that it cannot light up the Moon. As the Moon slowly passes through Earth’s shadow, the full moon gets darker and darker.

Soon, the Moon enters the darkest park of Earth’s shadow, the umbra. The Moon then becomes almost completely dark.

Red Moon

The Moon is not completely black during a total eclipse. It can turn different colours, but is usually reddish brown. This happens because light from the Sun bends slightly as it passes through Earth’s atmosphere. Some sunlight passes around Earth and hits the Moon. The light is reddish in colour because dust in Earth’s atmosphere scatters the different colours that make up sunlight in different directions. The dust lets only the red part of the light pass through. How red the Moon is during a total lunar eclipse tells scientists how much dust there is in Earth’s atmosphere.

The Moon’s Surface The Moon is covered with dry, powdery gray soil. Nothing lives on the Moon. There is no liquid water on the Moon’s surface. The Moon has no atmosphere – therefore there

are no clouds, rain or wind. The force of gravity on the Moon is six times

weaker than on Earth. This is because the Moon’s mass is 80 times smaller than Earth’s mass – the more mass something has the greater the force of gravity.

Midday temperatures at the Moon’s equator can reach 130ºC. All of this heat escapes at night and it can get as cold as -170ºC.

Man on the Moon

Astronauts from Apollo 11 were the first humans to walk on the Moon. They could only make one trip outside their lander. They spent 2.5 hours walking on the Moon before they climbed back into the lander.

What to do on the Moon?

On each of the following Apollo missions, astronauts spent more and more time on the Moon’s surface. During the Apollo 16 and 17 missions, they made several trips out of the lander and spent over twenty hours at work on the Moon’s surface. Apollo missions stopped after the Apollo 17 mission in December 1972. From 1998 to 1999, a space probe called the Lunar Prospector orbited the Moon to collect geological data. Scientists programmed it to crash on the Moon’s surface, hoping it would break through to water, but none was found.

What to do on the Moon?

While they were on the surface of the Moon, the astronauts performed many tasks. They collected rock samples and also left equipment and experiments behind. These items sent information back to Earth long after the astronauts were gone.

Please Copy This Down

Age 4.5 billion years (about the same as Earth)

Average Distance from Earth

384,000 kilometers

Diameter 3476 kilometers

Period of Revolution 27 Earth days

Mass 7.35 x 1022 kg.

Temperature Range 130ºC at the equator at midday to -170ºC at night.

The End