What are the craters on the moon

Why does it look different on earth than on the moon?

It doesn't look very inviting on the moon: the surface is dry and covered with a layer of gray dust. Meteor impacts have torn huge craters in the ground that filled with lava from inside the moon. Around these lava basins, kilometer-high crater edges pile up as mountain rings.

Our blue planet is completely different - if only because three quarters of it is covered by water. The water not only covers a large part of the earth, it also forms its land mass: rivers, glaciers and the surf of the sea process the rock, crush it and move it around. This is how valleys, coasts and ever new layers of rock are created.

The interior of the moon is solid and rigid today. The earth, on the other hand, has a liquid mantle on which movable plates float. The movement of the tectonic plates causes mountains to unfold, deep-sea trenches to form and volcanoes to spew fire and ashes.

Unlike the moon, the earth has a shell of air, the atmosphere. The weather is created in this atmosphere. Wind, rain and snow have worked and shaped the earth's surface over millions of years. In addition, the atmosphere acts as a protective shield that slows down meteorites and lets them burn up.

Because the moon has no such atmosphere, meteorites hit its surface unchecked and suddenly crumble the rock into dust. But meteorites are the only forces that shape the lunar landscape. Because there is no water, no atmosphere and no plate tectonics, the influences that make our earth's surface so varied are missing.

The first people to step onto the barren moonscape were astronaut Neil Armstrong and his colleague Edwin E. Aldrin. The footprints that they left when they landed on the moon in 1969 can still be seen today - because neither wind nor water cover their tracks on the moon.

21.7.1969

Tense waiting in the control center. A series of warnings from the on-board computer almost led to the mission being aborted, now this: The planned landing site is littered with small craters and rocks. Commander Neil Armstrong grabs the control stick and tries to land the lunar module by hand. But the fuel is running out ...

Finally the redeeming radio message comes: “The eagle has landed.” For the first time, a spaceship with people on board touched down on the moon. A few hours of rest and preparation, then Armstrong opens the hatch and climbs down the ladder. With the words "a small step for a person, but a gigantic leap for mankind" he is the first person to set foot on the moon. Shortly afterwards his colleague Buzz Aldrin follows.

The stay is only short: in two and a half hours on the lunar surface, the astronauts set up an American flag, collect a few kilograms of lunar rock and set up various scientific experiments on the lunar surface.

After another pause, they ignite the engine and fly back into a lunar orbit. Michael Collins is waiting there in the Columbia space capsule, which is supposed to bring them back to Earth.

A tape measure to the moon

Among the devices Aldrin and Armstrong placed on the moon was a special mirror. It is constructed in such a way that it reflects every ray of light back to its starting point. With a well-aimed laser beam, scientists can now take aim at this mirror - and stop the time until the reflected laser beam arrives at them again. If the watch is accurate enough, you can measure the distance to the moon to within a few millimeters. They made a surprising discovery: the moon moves about 3.8 centimeters away from the earth every year!

What are asteroids, meteorites and comets?

On some nights you can observe a special moment in the sky: it looks like a star is falling from the sky. Superstitious people even think that whoever sees such a shooting star could wish for something. But what is really behind it and where do the shooting stars come from?

In our solar system there are not only the sun, planets and moons. Many small pieces of rock and metal have also been discovered. They are much smaller and not as nicely round as planets, hence they are called minor planets or Asteroids. Like their big siblings, they circle the sun in regular orbits. Most asteroids can be found in the "asteroid belt" between the orbits of Mars and Jupiter.

Every now and then two of these asteroids collide. A crash like this creates a lot of debris and splinters. These fly away from the previous orbit, across the solar system. Some of them get close to the earth, are attracted to it and fall to the earth. These falling chunks are also called meteorite.

On earth they would literally fall like a stone from the sky - if it weren't for the atmosphere. Because the meteorites are so fast that the air cannot move to the side quickly enough. The air in front of the falling rock is compressed and therefore extremely hot. The air begins to glow and the meteorite begins to evaporate. We can then see that as a glowing streak that moves across the sky - a shooting star.

Most meteorites are so small that they burn up completely as they travel through the air. The trail then simply ends in the sky. Larger debris also lose mass on the way, but does not completely evaporate. They reach the ground and strike there.

What these meteorites do to the earth depends on how big they are. Small meteorites a few centimeters in diameter, for example, just leave a dent in a car roof.

The largest known meteorite hit about 65 million years ago. It was several kilometers in diameter and tore a crater 180 kilometers in diameter. The impact threw so much dust into the air that the sun was eclipsed for hundreds of years. As a result, plants and animals all over the world died out - this was the end of the dinosaurs.

Fortunately, such large meteorites are very rare so we don't have to worry. In addition, unlike the dinosaurs, we can observe the sky with telescopes and discover such large asteroids long before the impact.

While a shooting star burns up in a few seconds, another phenomenon remains visible longer: Comets with its tail there are days or weeks in the sky. In the past, people also attributed many properties to them - as divine signs, heralds of calamity or harbingers of happy events. But the truth is a little less spectacular.

Astronomers also call comets "dirty snowballs". They come from the outer solar system, far from the warming power of the sun. It's so cold there that water immediately freezes to ice. This is how lumps of ice and dust form - dirty snowballs.

Even a comet initially travels far away from the sun - until it is deflected by a collision and flies in the direction of the inner solar system. It gets closer to the sun and over time receives more and more light and warmth. This will cause the frozen surface to begin to thaw and even to evaporate. This creates an envelope of water vapor and dust around the comet.

At the same time, the comet gets to feel the “solar wind” - tiny particles that fly out of the sun at high speed. They hit the comet's vapor envelope. This will blow away the comet's vapor envelope, creating an elongated cloud that points away from the sun. When this cloud is then hit by sunlight, it appears as a glowing streak - the comet's tail.

The comet makes an arc around the sun and then moves away again. When it is far enough away from the sun, thawing and evaporation will also stop. The tail disappears and the comet moves like a dirty snowball through the vastness of the outer solar system. Depending on the comet's orbit, it will take many decades or even centuries before it comes close to the sun again.

Why does the moon have spots?

The man in the moon - known from songs, films and stories. Indeed, there are conspicuous dark spots on the lunar surface, and with a little imagination you can see a face in them. But what are these spots really?

At first, scientists thought the dark spots were seas. But at least since the first visit to the moon in 1969 it has been clear: The moon is dust-dry, the entire surface of the moon consists of fine gray rock powder. And the dark spots are great plains that are simply filled with darker dust. This makes the moon appear speckled light and dark. But how did these plains come about?

The lowlands are almost as old as the moon itself. When the surface of the moon had already solidified into a crust in the early days of the solar system, large asteroids repeatedly hit the moon and tore holes in the fresh crust. There lava ran out of the still hot, liquid interior of the moon and filled the plains. Lava rock is darker than the crustal rock, so the plains appear darker.

There are now hardly any large asteroids hitting the moon, but still a lot of smaller ones. Since the moon (unlike the earth) has no atmosphere, they do not burn up but hit the surface. Most of the time, the force of the impacts is only enough to crumble some rock and stir up a bit of dust, which quickly sinks back to the ground. Therefore, the surface of the moon today consists of rock dust, mainly of light crustal rock and, in the lowlands, of darker lava rock. From the earth it looks like spots, seas - or a face.

The blue planet

Seen from space, the globe appears in a strong blue. This is because almost three quarters of the earth is covered with water. Small amounts of water are transparent, but from a certain depth onwards it becomes more and more blue. Because we see the mighty oceans blue, the earth is also called "the blue planet". The term south of the equator is particularly applicable. Because the southern hemisphere is almost completely covered by the sea, because a large part of the continents have migrated to the north due to plate movement.

The vast oceans contain almost all of the water on earth. There is a lot of salt dissolved in sea water, which is why it is not suitable as drinking water. The little fresh water on earth is frozen mainly in glaciers and ice caps. Only a tiny fraction of freshwater is found in groundwater, in lakes and rivers, or in the air.

But the view from the outside is deceptive: the earth's surface is largely covered by water, but measured by the diameter of the earth, the oceans are only a very thin layer. Therefore, the water makes up only a fraction of the earth's mass. For comparison: if the earth were the size of a basketball, all of the water on earth would fit into a table tennis ball. And the drinking water would be proportionally even smaller than a single popcorn.

The water cycle

The water on earth is always on the move. Huge amounts of it are constantly moving - between sea, air and land - in an eternal cycle in which not a single drop is lost.

The motor of the water cycle is the sun: It heats the water of the seas, lakes and rivers so much that it evaporates. Plants also release water vapor into the atmosphere through tiny openings. The humid air rises, tiny water droplets gather in the air and form clouds. As rain, hail or snow, the water falls back into the sea or onto the earth. If it falls on the ground, it seeps into the ground, supplies plants or flows through the ground, over streams and rivers back into the sea. The eternal cycle of evaporation, precipitation and runoff starts all over again.

The water cycle has been around for almost as long as the earth has existed. He ensures that living beings on our planet are supplied with fresh water. And not only that: Without the water cycle, the weather as we know it would not exist.

From rock to grain of sand - weathering

Today the north of Canada is a gently undulating landscape. However, many millions of years ago there was a mountain range here. In fact, even high mountains can turn into small hills over a very long period of time.

The reason for this transformation: The rock on the earth's surface is constantly exposed to wind and weather. For example, if water penetrates into cracks in the stone and freezes, it splits the stone apart. This process is called frost blasting. The rock also becomes brittle through temperature changes between day and night and through the power of water and wind. In other words: it weathers. This process can also be observed in buildings or stone figures. During the weathering, the rock breaks down into smaller and smaller components up to fine grains of sand and dust. Different rocks weather at different rates: Granite, for example, is much more resistant than the comparatively loose sandstone.

Some types of rock even completely dissolve when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt - and that already dissolves in ordinary water. Lime is somewhat more stable, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. The weathering leaves rugged limestone landscapes on the surface of the earth, and caves are formed below the surface.

But not only solution weathering, heat and pressure also wear down and crumble rock under the earth's surface. Wherever plants grow, roots dig in, break up the rock piece by piece and also ensure that it is removed millimeter by millimeter.

In this way, weathering not only works on individual rocks, it gnaws at entire mountain ranges. It will take a few million years for the Black Forest to be as flat as northern Canada.

What causes erosion?

When rock weathers, it seldom remains in its original location. Rock debris often rolls down the slope, is washed away by the water or pushed away by masses of ice. The wind can also carry fine rock dust or sand with it. Regardless of whether the rock is removed by water, ice, wind or gravity, all of these processes are called "erosion".

The erosion by running waters is particularly drastic. Streams and rivers dig a bed in the ground, rock slides down, a valley forms. If a glacier rolls down the valley, it planes this valley wider through the scree it has carried along with it. Long after the ice has melted, you can tell from such trough valleys that there was a glacier here. The surf of the sea, on the other hand, attacks the coast. Steep cliffs are hollowed out and collapse, sandy beaches are washed away by the waves. In deserts, the wind sweeps away large areas of sand. The harder it blows, the more sand it can take with it. A sandstorm gradually removes obstacles made of solid rock like a sandblasting fan.

When rain and wind wash or blow away the soil cover over large areas, we speak of soil erosion. Soil erosion is also used in the case of landslides on slopes. The problem: The fertile upper layer of the soil disappears. In the worst case, it can no longer be used for agriculture.

If the soil is overgrown with plants, this slows down erosion. The roots of the plants hold the soil in place and prevent the wind and water from carrying it away. If the plant cover is destroyed, for example by deforestation, the soil lacks this support and it is eroded.

Continents on the move

For a long time it was thought that the land masses of the earth would stand rigidly in place. It later turned out that the opposite is the case. The continents of our planet are moving! Like huge ice floes, they drift in different directions, albeit not very quickly. Their speed corresponds roughly to the growth of a fingernail. But why is it that the continents are constantly on the move?

The earth's crust that envelops our planet is brittle and cracked. It resembles a cracked egg shell and is made up of seven large and many smaller plates. Some of them make up the continents, others make up the ocean floor. These plates of the earth's crust float around on a hot, viscous rock slurry and are driven by movements in the earth's interior, more precisely: by currents in the earth's mantle. Experts also say: you are drifting. All of these processes related to the movement of the earth's plates are called plate tectonics, and the movement itself is also known as plate drift.

The earth is particularly active where the individual plates adjoin one another.At some of these plate boundaries, hot rock penetrates upwards from the earth's mantle and cools down. Here new earth crust forms: the two plates grow and are thereby pushed apart. On the other hand, where two plates collide, the lighter one of them - the continental crust - is crumpled up and unfolded to form mountains. The heavier of the two - the oceanic crust - is slowly disappearing into the depths. Due to the heat in the earth's interior, their rock is melted again. As the edge of the plate sinks into the depth, it pulls the rest of the plate behind it and thus additionally drives the plate movement.

Volcanic eruptions, earthquakes, long mountain ranges and deep ocean trenches accumulate along such plate edges. Most of the unrest on the earth's surface brings with it the largest of its plates: it is the Pacific plate, which is moving northwest at a rate of about 10 centimeters per year. Most of the world's active volcanoes can be found at their edges, and violent earthquakes shake the region. Because of the frequent volcanic eruptions and earthquakes, this plate boundary is also called the “Pacific Ring of Fire”.

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital for us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a huge impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8000m high in the Himalayas therefore usually take artificial oxygen with them on their tour.