What came first or space

21.7.1969

Tense wait 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!

24.12.1968

Upside down world - the earth rises above the moon horizon. The American astronaut William Anders took this famous photo on Christmas Eve 1968.

Together with Frank Borman and James Lovell, he circled the moon several times on the Apollo 8 mission. When their space capsule came out from behind the moon during one of these orbits, they saw the globe emerge behind the lunar horizon. They were deeply impressed by the sight and took several photos - although Anders jokingly remarked that this was not provided for in the mission plan.

A real "earth rise" - like the way we see the moon rise while standing on earth - cannot be experienced on the surface of the moon. Because the moon always turns the same side to the earth. If you stay on this side, you can see the earth all the time - and always in the same place in the sky. And from the back of the moon, the earth can never be seen.

The second face

The moon shows itself from a completely new side: On October 7, 1959, the Russian probe "Luna 3" took the first photo of the back of the moon. However, the world had to wait eleven days for this historic photo: it was only when the probe flew back towards earth that the radio link was good enough to send the image.

At first glance, the picture doesn't look very spectacular. The resolution is poor, and since the sun shines almost perpendicularly on the surface of the moon, no shadows from mountains and craters can be seen.

But there was a surprise: The moon has far fewer dark spots on the back than on the front. Astronomers are still puzzling over the reason!

Until this photo was taken, mankind had no idea what it looked like there. Because from the earth you only ever see the same side of the moon.

What is the moon

It is the brightest celestial body in the night sky: the moon. It shines so brightly on full moon nights that some people find it difficult to sleep. It appears as big as the sun and the stars look like tiny points of light next to it.

But the impression is deceptive: In reality, the moon (diameter: 3474 km) is only about a quarter the size of the earth (12742 km) - and the sun (1.39 million km) is even four hundred times larger. The moon only appears the same size to us because it is so close to us - the sun (distance to the earth about 150 million km) is also about four hundred times further away than the moon. (384,400 km, an airplane needs 18 days for this distance!)

The bright light is also deceptive: unlike the sun, the moon does not shine by itself, but is illuminated by the sun. Some of this light is then reflected back from the surface of the moon and hits the earth. Just because the moon is so close to us, enough light arrives on earth to light up the night - at least if the moon doesn't just seem to have disappeared without a trace ...

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 lowlands. Lava rock is darker than the crustal rock, so the plains appear darker.

In the meantime, hardly any large asteroids hit 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 light crustal rock and, in the lowlands, darker lava rock. From the earth it looks like spots, seas - or a face.

Why do planets have moons?

Earth has one, Mars has two, Jupiter and Saturn even over sixty each! Only two planets in the solar system have to do without moons: Mercury and Venus, all other planets have at least one moon. But why do most planets have moons? And what is a moon anyway?

For us, the moon is first and foremost the bright circle that stands in the sky at night. It looks small, but in reality it is a large rock ball 3475 km in diameter that circles the earth. And it is exactly the same with the other planets: They are also orbited by smaller or larger celestial bodies on regular orbits. Astronomers also call these celestial bodies “moons”.

To get to a moon, a planet usually has two options: Either the moon is created together with its planet, or the planet is created first and later captures a smaller celestial body.

These smaller celestial bodies are asteroids that fly ownerless through the solar system. When they get near a much larger planet, they are drawn to its gravity. This forces the asteroid into an orbit around the planet - the planet has got a moon. This “catching” of a moon works better, the heavier the planet is. This is why the large and heavy planets Jupiter and Saturn also have most of the moons in the solar system.

Other moons formed from debris left over when their planets formed: In the beginning, the solar system was nothing but a large disk of dust, gas, and ice. In the middle, the matter agglomerated particularly strongly - here the sun was created, surrounded by the remaining disk of dust, ice and gas. The same thing was repeated on a small scale in this disk: compact lumps formed again - the planets - and the remaining dust collected in a disk. And if there was enough matter in this disk, even smaller lumps formed there: moons. (Only when the gravitational pull of the planet was very strong were the lumps immediately torn apart. This was the case, for example, close to Saturn, which is still surrounded by rings of dust to this day.)

Both moons that emerged from the dust debris and the captured moons are much smaller than their planets.

The earth is the big exception: its moon is much larger than it should be compared to the earth. Therefore it can neither have originated from leftover dust nor simply been captured. Instead, the earth owes its moon to a cosmic catastrophe that almost destroyed the planet:

Shortly after the earth was formed, it collided with a celestial body that was about half the size of itself. The force of this impact cannot be imagined: The explosion was so strong that most of the young earth melted again - and the other celestial body as well. Part of the molten mass was thrown away and gathered in an orbit to form a second ball. Over time, these two spheres cooled and solidified again. Today the larger sphere orbits the sun as the earth - and the smaller one orbits the earth as the moon.