What is left on the moon

How do the phases of the moon arise?

The moon is funny: it changes shape all the time. Sometimes it's round like a disc, sometimes just a thin sickle - and sometimes we don't see it at all. Why is that?

The moon (like the earth) does not shine by itself. We only see it because it is illuminated by the sun. More precisely, we can only see half of the lunar sphere that faces the sun. The other half doesn't get any light and stays dark.

What we see of this half changes over the course of a month as the moon orbits the earth once. When we see it from the earth with the sun behind us, we look closely at the illuminated side and see the moon fully illuminated, as a full circle. (Therefore: "Full moon“)

If the moon moves further on its orbit, that changes: The rays of the sun now hit it from the left as seen from us. The right edge is not illuminated, so it is not visible. The visible part of the moon continues to decrease on this part of the orbit. ("waning moon“)

Two weeks after the full moon, the moon is facing exactly in the direction of the sun, the side facing us is completely unlit - the moon seems to have disappeared. This point in time is called "new moon“, Because the moon does not disappear permanently, of course, but continues to run and appears again in the sky.

Because little by little, some rays of the sun hit the side facing us again. Because the waxing moon is now on the other side of the earth than when you were losing weight, the rays of the sun now come from the right as seen from us. At first we only see a narrow strip on the edge, but it quickly widens. After a week, half of it is illuminated - we are looking precisely from the side at the light-shadow boundary.

And a week later we see the moon again with the sun behind us as a fully illuminated circle in the sky - and the process starts all over again.

23.1.2012

The noise is supposed to drive away the annual monster Nian - for this reason the Chinese greeted the New Year with bombastic fireworks on the night of January 23rd. The New Year in China is the most important festival of the year and is celebrated for two weeks with many events.

In the Chinese calendar - unlike ours - the year does not begin until the first new moon of the year. The traditional Chinese calendar divides the year into twelve phases of the moon - the moon needs about 29.5 days from full moon to full moon. The New Year celebration falls on a different date each year, but is always between January 21st and February 19th.

The New Year is the most important festival of the year for all Chinese people around the world. But it no longer has any practical meaning: Since the establishment of the Chinese Republic at the beginning of the 20th century, our Gregorian calendar, which is based on the sun, has also officially been in effect there. So the Chinese can celebrate the turn of the year twice.

Hair off at the full moon

Cutting hair, washing clothes and dieting with the waning moon? Watering flowers and fertilizing fields when the moon is waxing? Many people believe in the influence of the moon on humans. Lunar calendars are really "in" again these days. They give tips on which activities are best to do or not to do during which moon phases.

Scientists can only shake their heads at such superstitions, because all research has shown that the phases of the moon have no effect on things like hair, flower growth or human metabolism. So we can confidently go to the hairdresser whenever we want.

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 seems 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 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. In this disk the same thing was repeated on a small scale: again compact lumps formed - the planets - and the remaining dust collected in a disk. And if there was enough matter in this disk, smaller lumps were 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. That is why 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.

ebb and flow

Anyone who has already vacationed at the North Sea or the Atlantic knows the problem: You go to the beach to swim and the water is much further away than when you last bathed. The water level has sunk: it is ebb tide. If you want to get into the water now, you either have to walk a bit over damp sand and silt or wait a few hours until the tide comes in and the water rises again.

Ebb and flow alternate in a regular rhythm. This change is called the tide. The time interval between ebb and flow is a little more than six hours. There are twelve hours and 25 minutes between one flood and the next. How much the water rises and falls depends on the coast. At the North Sea, the difference between high and low water is about two to three meters. Elsewhere, however, it is much larger: In the Bay of Fundy in Canada, the water level fluctuates by 15 to 21 meters - this is the highest tidal range in the world!

But why is it that the water sloshes back and forth in the oceans? The solution lies in the gravitational pull of the moon. This force causes two huge flood mountains under which the earth rotates. One of the two comes about directly through the gravitational pull of the moon, because it pulls the water towards itself. The second flood mountain is exactly on the opposite side of the earth. This arises because the earth does not rotate perfectly evenly due to the gravitational pull of the moon, but “rocks” a bit. As a result, there is a centrifugal force that pulls the water away from the moon. Both flood mountains are about half a meter high.

Not only the moon, but also the gravitational pull of the sun has an effect on the water. If the sun and moon are on the same line, the tide rises higher than normal due to the mutual attraction: there is a "spring tide". If, on the other hand, the sun and moon are at a 90 degree angle to the earth, their forces partially cancel each other out. The result is a less high tide, the nipp tide.