How the earth, moon and sun work
How do solar and lunar eclipses arise?
When the sun or moon darkened, people used to fear the worst: misfortunes, catastrophes or even the end of the world. Today we laugh at this superstition. Nevertheless, a solar or lunar eclipse is an impressive experience. But how does it come about?
We know: the moon orbits the earth. If it moves exactly between the earth and the sun, it throws a shadow on the earth. From our point of view, it then covers the sun during this short time and it becomes almost as dark as at night - although it is actually day. A solar eclipse has occurred.
In the case of a lunar eclipse, it is the other way around: The moon is then exactly behind the earth as seen from the sun - which throws a shadow on the moon. For us, the moon is then only faintly visible, mostly in a reddish or brown color.
But why are solar and lunar eclipses such rare events? Shouldn't a lunar eclipse occur every time a full moon and, conversely, a solar eclipse occur at a new moon?
No, because when the moon is full or new, the three celestial bodies are almost never lined up exactly on one line one behind the other. The reason for this: the orbit of the moon is slightly tilted compared to the earth's orbit. The moon is therefore usually a bit higher or lower than the sun and earth. Then the sun's rays have a free path, the shadow of the moon passes the earth or the moon flies past the earth's shadow.
Only very rarely is the moon exactly in the right place at exactly the right height, so that the sun, earth and moon are lined up on a line and the moon's shadow falls on the earth - or the earth's shadow falls on the moon.
And even if a solar eclipse occurs, it can only be seen for a few minutes, and not even anywhere on earth. This is because the moon is much smaller than the earth and only casts a small shadow on the globe. And since the moon is constantly in motion, its shadow moves quickly and the spectacle is quickly over. A lunar eclipse takes a little longer. Since the moon is smaller than the earth, it is completely covered by the earth's shadow and it also takes longer to come out again.
You don't experience a total solar eclipse every day. The Stuttgarters were all the more disappointed when a thick blanket of clouds blocked their view of the black sun. And instead of sunglasses, umbrellas were unpacked, because at the time of the solar eclipse, heavy rain pelted down. The event lasted only two and a half minutes. The sky darkened and really created a doom and gloom. And what probably annoyed the people of Stuttgart the most: At the decisive moment, of all places, a hole in the cloud cover opened up over the eternal local rival Karlsruhe and gave a view of the darkened sun.
The last total solar eclipse was seen in Germany in 1887, and the spectacle will only repeat itself in 2081. The media had announced the rare event as a spectacle long in advance and reported live in many cases - if there was something to see.
The umbra of the moon first hit the globe east of New York. In a few hours it then moved 14,000 kilometers across Europe to India, where it disappeared again from the surface of the earth in the Bay of Bengal. The European neighbors were also disappointed by the eclipse of the century due to the bad weather. Only in countries like Iran or India was there a clear view all the time and there was a big celebration.
Box seat above the clouds
Rich Americans and British have paid over € 4600 to get one of the coveted seats in the supersonic aircraft “Concorde”. While most people in Europe were annoyed by the cloudy sky on the ground, the Concorde overcame all obstacles: It simply flew after the moon's shadow and thus offered the occupants a view of the darkened sun for almost six hours. Nevertheless, there were complaints: Because of the crowd at the window seats, some passengers had no clear view of the solar eclipse - and asked for their money back.
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.
Why can we see the moon during the day too?
The tasks are clearly distributed: the sun shines during the day and the moon shines at night. But that's not true at all: the moon can sometimes be seen during the day - what is it doing there?
Day and night have a simple cause: the earth rotates. If our location on earth is pointing towards the sun, it is light, i.e. day. Later, when the earth continues to rotate, our location moves to the side facing away from the sun. We watch the sun go down and it gets dark.
The moon rises and sets too - for exactly the same reason: because the earth rotates. But the moon also moves: in the course of four weeks it circles the earth once. Half of this time, its orbit is on the side of the earth facing away from the sun. From there you can always see it when your position has just turned away from the sun - or in short: when it is night. But two weeks later the moon is on the side facing the sun. Then it is exactly the other way round: You can see it together with the sun during the day when your own location is facing the sun.
So the moon can sometimes be seen during the day and sometimes at night, even if for us it actually belongs to the night. But that's simply because the moon is the brightest light in the sky at night and is therefore much more noticeable.
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.
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