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Our Marvelous Moon

Orbiting around Earth at an average distance of 384,392km is our constant companion, the Moon.

The Moon is Earth's only natural satellite which means the Moon orbits the earth all year long. Earth has many man-made satellites orbiting it too.

©NASA

The Moon goes through phases that make it look a little different every night. But it’s always there, working hard for Earth. It makes the tide go in and out. It lights up the night. And it’s been the subject of stories, legends, poems, and songs since way, way back. The Moon is marvelous. And there’s way more than meets the eye.

The Moon Rocks

The Moon is about one-third the diameter of Earth. It’s made of rock, like Earth. In fact, all the elements that make up Moon rocks can be found on Earth too. These include oxygen, silicon, magnesium, iron, calcium and others.

How do we know what Moon rocks are made of? Scientists have analyzed 382 kg of Moon rocks and dirt that astronauts have brought back to Earth. That’s how they also know that the Moon is about the same age as Earth. 

Covered with Dust

Astronaut Edwin “Buzz” Aldrin was one of the first humans to walk on the moon and he photographed the footprint he left in the lunar soil.

©NASA

Covering the Moon’s surface is a thin layer of dust. The dust has been falling through the spaces between planets for millions of years. Because the Moon has noatmosphere, there is no weather and no erosion. So what’s rocky stays rocky, and what’s dusty stays dusty. The footprints left by astronauts walking on the Moon in 1969 are exactly the same now as they were then!

How Was the Moon Formed?

Many scientists believe that the Moon is a huge chunk of Earth. They think that back when Earth was just forming, a Mars-sized meteorsmashed into it. The crack-up hurled material out into space, and that material became the Moon.

Other scientists think the Moon formed elsewhere in the solar system. Somehow it got sucked into Earth’s gravitational field. But since no one was around back then to see it happen, no one knows for sure how the Moon came to be.

Many Moons, None the Same

Io, Europa, Ganymede and Callisto are Jupiter’s four largest moons also known as the Galilean Satellites. Earth’s moon is about the same size as Jupiter’s smallest Galilean Satellite.

©NASA

What makes a moon a moon and not a planet? It’s all about which objects orbit which. Planets orbit the Sun. Moons orbit planets. Moons are natural satellites that are held in orbit by a planet’s gravity.

Five planets besides Earth have their own moons. Jupiter has at least 63. There are 162 known moons in our Solar System, and they’re all different. Some have volcanoes, some have atmospheres and some may even have water. 

Earth and Moon in Step

From Earth we can only see one side of the Moon, sometimes called the near side. The photo shows the other side of the moon, the far or dark side we never get to see.

©NASA/JPL

When we look up at the Moon, we always see the same rocky face reflecting the sun. We never see the other side, or dark side, of the Moon. This is called synchronous rotation. It means Earth and the Moon are turning together, as if they’re dancing to the same music.

Ancient Oceans? Well, Sort of 

When we look at the Moon, we also see wide, smooth, dark places.  Scientists used to think these were ancient oceans and actually named the areas mare—Latin for “sea”. These places go back to the time millions of years ago when the Moon was not solid rock. It had a hot liquid center. In weak places of the crust, lava would blast through, forming volcanoes and mountains. 

In a special type of image, we can see how different each of the moon’s “seas” are. The blue color shows an area with a lot of titanium, a kind of metallic element.  The orange area is a different color because it has less titanium.

©NASA

When the Moon got whacked hard enough by a meteoroid or asteroidthe crust would break. More lava would ooze up and out into a smooth pool. Then it would cool down. So those large, dark places are oceans, in a way. They’re seas of cooled lava.

Craters are the Pits

We can also see holes and canyons on the Moon’s surface. These pits are old scars from asteroids andmeteors that smacked into the Moon and exploded. 

The far side of the Moon has many craters. This particular crater is 80 kilometers (50 miles) in diameter!

©NASA

The largestcrater on the Moon is also the largest crater in the entire solar system. It’s called the Aitken Crater, and it is found at the south pole of the Moon. It measures2500 km in diameter and is 13 km deep.

The far side of the Moon has lots of craters because it faces open space. The side of the Moon facing Earth has fewer craters. That’s because our planet protects it from falling space debris.

Why don’t we have craters on Earth? We do have a few. But our atmosphere makes most flying space objects burn up before they can crash into us and make a dent.

Where’s the Water?

There is no water on the Moon, but scientists think there may be small areas of ice. Comets and meteoroids can leave ice behind after a collision. Usually the Sun hits these ice patches and breaks them down into hydrogen and oxygen atoms, which escape into space. But there are some areas of the Moon that are always in shadow. If ice has collected there, it may still be there.

The Moon’s Orbit and Phases

It may seem like the Moon changes shape, but it really doesn’t. What changes is the amount of the Sun’s light reflected on the Moon as it moves around us. That’s why it looks different night to night.
Here’s an example. When the Moon is between the Earth and the Sun, its daylight side is turned away from us. We can’t see anything. This is called the new moon. As it keeps turning around Earth, more and more surface becomes visible. Finally, the entire sunlit side is visible. This is called a full moon.

It takes our Moon about a month (29.5 days) to orbit around Earth. It also takes about a month (27.3 days) to rotate on its own axis.

When the tide goes out there are sometimes animals or other objects left behind such as seashells or jellyfish.

©G.Ellis/GLOBIO.org

What Does the Moon Have to Do with Ocean Tides?

Earth and the Moon have been in a wrestler-hold of gravity for as long as time. Earth pulls on the Moon and keeps it in orbit, but the Moon also pulls on Earth. When it pulls on the oceans, the water bulges out toward the Moon. When the water bulges up, we get high tide. When it bulges away we have low tide.

Lunar Eclipse

During the total lunar eclipse of October 2004 the ground on the Moon looked red.

©Doug Murray

When Earth passes in between the Sun and the Moon, our shadow falls on the Moon and we see a lunar eclipse. You might think we’d have a lunar eclipse every month, because the moon moves around us as we move around the Sun. But the orbit of the Moon is angled in a way that makes these eclipses happen only once in awhile.

Studying the Moon Long Ago

Nearly every culture has myths about moon gods or goddesses that influenced life on Earth. The bright light in the night sky must have been an awesome comfort in the days before fire. It must have also been the subject of legends, stories and myths later on, as people gathered around fires. Eventually people created tools to study our heavenly neighbor.

Early Greek scientists studied the shadows on the Moon and estimated the distance. And in 1610 Galileo looked at the Moon with his early telescope and was the first to describe the surface.

Studying the Moon Today

The Moon is the only other place in the solar system that humans have actually visited so far. In 1959, the Soviet Union sent Luna 2 to the Moon to orbit around and make observations. On July 20, 1969, the American Apollo 11 mission sent the first humans to land on the Moon. Since then there have been 6 Apollo missions and 12 astronauts who have walked on the Moon.  The last Moon visit was in December 1972.

An astronaut from mission Apollo 11 completes tests and collects samples from the Moon that will be studied by scientists back on Earth.

©NASA

In 1994, the U.S. spacecraftClementine mapped the Moon. In 1999 the Lunar Prospector was sent to map the Moon with even more detail.
NASA has plans to create a Moon Base for people as early as 2020.

Studying the Moon Anytime

The Moon is just waiting for you to observe it on any clear evening. With the exception of the few evenings when the Moon is new you can always see something. Try looking at the Moon with binoculars or a telescope. Can you spot the dark and light patches? Can you see craters? Can you tell the phase of the Moon you’re seeing?