How did the heavenly bodies get their gravity?
What is our solar system and how did it come about?
The earth is not alone in space: people have been observing the sun, moon and stars in the sky for a long time. They discovered early on that some stars are moving. These wandering stars were observed and their paths followed. For a long time, however, their movements were not understood - until about five hundred years ago a man by the name of Nicolaus Copernicus solved the riddle: The earth and the "wandering stars" are actually planets that all circle the sun at different distances.
Today we know eight planets. To remember their names in the correct order, the first letters of the sentence "M.a Vater eclarifies mir jEden S.monday uurens Nachthimmel. “- or in short: M-V-E-M-J-S-U-N.
M.Erkur is the planet that orbits closest to the sun. Then come Venus, E.rde and M.ars. These four inner planets have a solid surface made of rock and are still relatively close to the sun - only a few hundred million kilometers.
They are circling further out, at a distance of about one to 4.5 billion kilometers from the sun outer planets: Jupiter, S.aturn with his rings, Uranus and all the way outside Neptun. They are made of gas (mostly hydrogen and helium) and are much larger than the inner planets. Jupiter and Saturn are about ten times the size of the earth, that's why they are also called that Gas giants.
And finally there are asteroids, comets, and clouds of dust that also orbit the sun. The gravitational pull of the sun holds all these heavenly bodies together and forces them to fly in a circle like on a long line. Everything together is called that Solar system. The moons are one of them - but they are held in place by the gravitational pull of the planets.
But why does the sun even have planets? This has to do with how the sun came into being: a cloud of gas and dust contracted by its own gravity and became a star. But not all of the material in this cloud was "built into" the star - around one percent was left over. And when the sun began to shine, the radiation pushed the remaining matter outwards again.
The light gases were pushed far outwards, the heavier dust and rocks remained close to the sun. From these clouds of dust and gas, the planets emerged over time. Therefore there are the gas planets outside in the solar system, further inside the rock planets - including our earth - and in the very center the sun. It contains 99% of the mass of the solar system and holds everything together with its gravity.
In the trial against the mathematician and astronomer Galileo Galilei (68) the verdict was reached. The judges of the Catholic Church agree: Galileo's “Copernican view of the world” contradicts the Bible. Galileo's claim that the earth revolves around the sun has been declared false and not proven.
In the Roman Dominican monastery of Santa Maria, the professor of mathematics had to renounce his teaching while kneeling in front of the guards of the Catholic Church. Instead of imprisonment, Galileo is now threatened with lifelong house arrest. With immediate effect, his books are no longer allowed to be published.
Galileo had observed the starry sky for years for his research. To do this, he used the latest technical tool, the recently invented "telescope". His observations allowed only one conclusion: the earth - like the other planets - revolves around the sun. The Church warned him on several occasions to be careful with such claims. In spite of this, the scientist vehemently advocated this “Copernican view of the world”.
The publication of his book “Dialogo” brought the barrel to overflowing: Pope Urban VIII reacted insulted, and so Galileo was brought to justice in Rome. The Church continues to insist on a literal interpretation of Scripture unless there is clear evidence against it.
Along with the condemnation of Galileo Galilei, the Church also forbade the teaching of the scientist Nicolaus Copernicus. His theory, published almost a hundred years ago, formed the basis of Galileo's scientific work.
The physician and committed amateur astronomer Nicolaus Kopernikus had published the book "About the revolutions of the heavenly circles" in the year of his death in 1543. In this he contradicted the official opinion of the church. He claimed that the earth was not the center of the world, but a planet that revolved around itself and the sun.
Copernicus must have guessed what this knowledge meant and feared the punishment of the church. Only shortly before his death did he allow his book to be published. Without his knowledge, however, a clergyman added a foreword. The “Copernican view of the world” was presented in it only as a pure hypothesis and calculation aid, not as a proven assertion. Copernicus could not contradict: he did not live to see the first publication of his book.
You have to search for a while in this picture: The sensation is a “pale blue dot”, a tiny light blue dot in the void. It is hard to imagine that this little dot should be our home!
This picture shows the earth. It was picked up by the Voyager 1 probe from the edge of the solar system - 6.4 billion kilometers from Earth. It is part of a unique group photo of our solar system, which is composed of a total of 60 individual photos and contains all planets except Mars and Mercury.
Although the picture has no scientific use, it shows a fascinating and eerie view of our planet: From this distance, the earth is just a tiny grain of sand in space, our island in the middle of an empty, hostile void.
The probe Voyager 1 and its identical sister, Voyager 2 were launched in 1977 to explore the outer solar system. In March 1979 she visited Jupiter, in November 1980 Saturn. It provided impressive close-ups of the moons and rings of both planets. On the further path of the probe, scientists hope to obtain new, interesting measurement data from the edge of the solar system - and the area beyond it.
Before it finally left the solar system, however, the scientists activated the camera one last time for these recordings.
A record for aliens
As with previous probes, NASA has also equipped Voyager 1 and 2 with a message to aliens. For this purpose, a copper plate was attached to the probe and covered with gold. Instructions for use on how to reproduce the images and sounds on the back are engraved on the front. Like a record, it contains greetings in 55 languages, animal voices and other noises from nature, music (including Bach and Mozart) and a personal address by the then US President Jimmy Carter. In addition, photos of life on earth and scientific graphics are stored there.
The idea behind it: These probes will leave our solar system and fly out into the void of space. There is nothing there to damage or decompose the probes. Hence, they could be the man-made objects that have existed the longest - estimated up to 500 million years!
The researchers were drawn to the following idea: What if, in the distant future, far away from the solar system, extraterrestrial astronomers discover, capture and investigate one of the probes? Then they decided to give their extraterrestrial colleagues some information about the builders of the probe, a kind of cosmic message in a bottle.
However, space is unimaginably large and empty. Therefore, it is very unlikely that aliens will actually find the probe. And even if: The earth will then look completely different - and then probably no people will be alive either.
What is a star
When it is particularly dark at night and the sky is clear, we see thousands of stars as tiny points of light twinkling over our heads. But why do the stars shine? What are stars anyway?
Stars are simply spheres of gas. But inside it is unimaginably hot, many millions of degrees Celsius. Because of the intense heat, the gas glows and glows - like a lightbulb, only much brighter. The light from the stars is so strong that we can see it from Earth, even though the stars are many trillions of kilometers away.
Stars appear to us like tiny points of light - but that's only because of the great distance: in reality, stars are huge. The smallest are about ten times the size of the earth, giant stars can be a hundred thousand times as big!
However, there is one star that is very close to us compared to everyone else: the sun. After all, it already appears to us as a bright disc in the sky. But even this impression is deceptive: the sun is about a hundred times the size of the earth. We see and feel its power every day, because it gives the earth light and warmth - like a large campfire, by which we sit in the cold universe.
However, a star does not burn wood. It consists mainly of hydrogen gas and draws its energy from the hydrogen atomic nuclei. So a star slowly burns itself, so to speak. When at some point the fuel supplies are used up, it becomes dark and collapses or explodes. Our sun will end like this one day too. But because stars are so big, the fuel lasts for a long time. Our sun, for example, will shine for another five billion years.
What is a planet
Perhaps one or the other has noticed a particularly bright star in the morning or evening sky: Venus. After the sun and the moon, it is the brightest object in the sky. Because it shines so brightly, it is also called "morning star" or "evening star" - much to the annoyance of astronomers: Because Venus is not a star, but a planet!
The most important difference: a star shines by itself, a planet does not. Stars have a source of energy inside them, so they glow hot and emit light. A planet, on the other hand, is cold and does not shine by itself. We can only see it when it is illuminated by a star. Then the surface of the planet distributes the star's light in all directions.
Most planets belong to one star. Because planets do not arise alone, but together with a star. They then belong to this star and orbit it - such as Earth and Venus, which orbit the sun.
And why is Venus so easy to see even though it only transmits the light of the sun? This is due to their thick cloud cover, which reflects sunlight particularly well. In addition, after the moon, Venus is the celestial body that comes closest to the earth: just 40 million kilometers - that is a stone's throw compared to the distances in space. Because it comes so close to the earth and its clouds reflect a lot of light, we can easily see it in the sky.
Of course, Venus is not the only planet. Like the earth, it is one of the eight planets in our solar system. And the sun is not the only star with planets either. Since there are an unimaginable number of stars, the universe just has to be teeming with planets.
Our solar system is one planet poorer. Pluto was the ninth planet for 76 years. Now his planetary title has been officially revoked. It is descending into the league of "dwarf planets", where it will play a much less important role in the future.
With the discovery of the “planet” Eris, the discussion flared up again: When is a celestial body a planet? Because if you want to continue counting Pluto as a planet, then you would have to admit that to the larger Eris and the somewhat smaller Makemake - and possibly other, as yet undiscovered celestial bodies.
The International Astronomical Union (IAU) in Prague has now made its judgment: Eris and his colleagues are only dwarf planets. Their mass, orbit and orbital plane around the sun clearly distinguish them from their larger counterparts. But also Pluto no longer falls under the planet definition and has to give up its title - equal rights for all.
Not everyone is happy with the IAU clarification. Opponents of this decision founded the organization "Pluto's Friends" and some even went to demonstrate. Your demand: Pluto must become a planet again.
Which is the tenth planet?
The decision to expel Pluto from the series of planets was preceded by years of searching for the “tenth planet”. Right at the forefront: the American astronomer Mike Brown, who specializes in the study of celestial bodies on the edge of the solar system.
As early as 2003 he discovered Sedna, which was already considered by some to be the tenth planet. But since Sedna was much smaller than Pluto, the list of planets remained untouched.
On July 29, 2005, the sensation was perfect: Mike Brown announced the discovery of three new celestial bodies - Eris, Makemake and Haumea. With an estimated 2400 kilometers in diameter, Eris is larger than the smallest planet to date, Pluto. However, due to its unusual orbital plane around the sun, it remained undiscovered for a long time.
This discovery made it necessary to have an official definition of what a planet should be. However, this definition did not lead to a tenth planet, but reduced the number of planets to eight.
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 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, 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. 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 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.
Why does Saturn have rings?
When the telescope was invented, humans were able to take a closer look at other planets for the first time. One thing caught my eye right from the start: Saturn with its rings.
From a distance, the rings look like a tight band around the planet. But with calculations and special measurements it was found that the rings consist of billions of small dust particles, ice crystals and rocks. They all orbit evenly around Saturn, namely in a dense, flat cloud, so that in the telescope they appear like a disk.
It used to look like this around all planets. But elsewhere, the chunks in the cloud of dust contracted over time and formed moons. The only thing that was not possible was directly around Saturn: Here, the gravitational force of the nearby giant planet was disturbing - the dust cloud still circles that way today. A little further away from Saturn this disturbance is weaker, so that Saturn moons could form there.
The other major planets - Jupiter, Uranus, and Neptune - also have rings. However, Saturn's rings are made of a particularly bright material and are therefore easiest to see in a telescope.
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