What celestial moons could humans inhabit?
Wikijunior solar system / solar system
Have you ever wondered about the things in the sky? The sun, the moon or the stars? People have been watching the sky for a long time to find out what's out there. We are always inventing new methods to learn more about space.
Planets are large balls of rock or gas that move around stars. We live on what we call earth. It moves around a star that we call the sun. There are seven other planets orbiting our sun, and a lot of smaller things too. We call the sun and all these things that move around it the solar system.
Long ago people did not understand that the planets and other things in the solar system move around the sun. They thought that everything around the earth was moving, including the sun. That seemed natural because we don't feel the earth moving, does it?
Anyway, about 500 years ago, a man named Copernicus claimed that all planets revolve around the sun. After another 100 years, Galileo began observing the sky with a new invention: a telescope. He showed that it is quite normal for the planets to move around the sun. Later, more and more people started observing the sky with a telescope. They began to learn how the planets and other things in the solar system moved.
Now we're sending rockets into space to find out more. Astronauts travel around the earth. Some of them landed on the moon. Robots can fly to other planets and take photos. We can see things that astronomers like Copernicus or Galileo could only dream of.
We can use powerful telescopes to see what is happening on other stars. We compare photos of distant stars with photos of the sun. We can analyze thousands of images of the planets to learn more about the earth. We want to learn a lot from the many things in our solar system, to imagine how it came into being a long time ago. We could also guess what might happen to it in the later future.
What is the solar system?
The sun is at the center of the solar system. It is a star like billions of other stars in the sky. The other stars are so far away from us that they look like tiny dots. The sun is important to us because it gives us warmth, light and energy to live. So without the sun there would be no life on earth!
All other things in the solar system revolve around the sun. The planets are the largest of these objects, and the earth is one of the eight planets. But the planets are quite different!
Many of the planets have Moons. A moon always orbits its planet. Mercury has no moon, neither does Venus, earth has one and Jupiter has 63!
The planets closest to the sun become the Inner planets called. These are Mercury, Venus, Earth and Mars. Behind it comes a wide ring from Asteroids, these are chunks of rock that are much smaller than a planet. This ring will Asteroid belt called. There is also a dwarf planet (smaller than a normal planet) called Ceres in the asteroid belt. Then come the outer planets: Jupiter, Saturn, Uranus and Neptune. Further out there are some dwarf planets. You may know one of them: Pluto, which used to be called a planet. Other dwarf planets are Eris, Makemake and Haumea.
The planets are named after Roman gods who were worshiped by humans long ago. You can easily remember the names and the order of the planets with a donkey bridge: „Mein V.ater eclarifies mir jEden S.monday uurens Neighth sky ". The first letters of each word stand for a planet: Merkur, V.enus, E.rde, M.ars, Jupiter, S.aturn, Uranus, Neptun. Because the "M" appears twice, you can easily remember that Mercury comes first.
Behind the orbit of Neptune there is another extensive ring, similar to the asteroid belt, the Kuiper belt. Spoken: \ Keupa \, Kuiper was the last name of the person who first wrote about this asteroid belt. Most of the bodies of the Kuiper Belt are very difficult to see in the telescope.
Outside the Kuiper Belt is still the Oort cloud. The scientists suspect that this is an area where the comets come from. It is very far from the Sun, much, much further than Pluto, more than 1000 times that far. It is, so to speak, on the edge of our solar system. And yes, "Oort" was the last name of the first person to write about this cloud.
There is dust in between all of these things. The dust particles are very far apart, but they glow in the light of the sun. They can be seen glowing in the east before sunrise in September or October. We call it the zodiacal light when the grains of dust are between the earth and the sun and Replywhen the dust grains are on the other side of the earth.
When parts of the dust hit the earth's atmosphere, they light up brightly. We call these shooting stars or meteorites.
Behind it is a large empty room with no air or other things. The star closest to our sun is thousands of times farther away than our entire solar system is. The universe is a really huge structure!
What holds the solar system together? [Edit]
Why do the planets orbit the sun? Why do moons orbit planets? Why doesn't the sun go away and leave the planets behind? The answer to all of these questions has to do with the Gravity to do. Gravity is the force of attraction that every mass exerts on every other mass. An object on earth is "heavy" because the earth pulls it down, the object falls because it is attracted to the earth. The gravitational pull between smaller bodies is too weak to be felt, but the gravitational pull of the sun and planets is quite strong as they are very massive.
We do not feel the gravitational pull of the sun because it also attracts the earth on which we are standing. But the sun's gravity is big enough not to let the earth fly away. Although the earth is moving so fast, it remains on orbit around the sun. It's like they're tied together invisibly. It works the same way with moons orbiting their planets. They are kept on their orbits by the force of gravity. Incidentally, the sun itself does not stand still in space. The whole solar system orbits the center of our galaxy. And everything holds together because there is gravitational force.
If the earth didn't move, it would fall into the sun because of the force of gravity. But since it moves very quickly around the sun and constantly flies "around the curve", it is pushed outwards, just as you are pushed outwards in a car in the curve. This force, which acts on every body that moves around a curve, is called centrifugal force or centrifugal force. (Centrifuges are devices in which liquids are rotated quickly and thus the heavier components of the mixture are pressed against the wall.)
The gravitational force and the centrifugal force keep each other in exactly the same equilibrium for each planet, and so they continue to orbit.
About gravity, mass and weight 
Matter is what all things are made of. The mass of a body tells us how much matter it contains. Two bananas have twice the mass of a banana. But a piece of iron, which is as big as a banana, has more mass, because in iron the matter is compressed more tightly (it is therefore heavier). The more mass a thing has, the more it is attracted by gravity and the more its gravitation attracts other objects.
We name the force with which the earth attracts us Weight. The astronauts weigh much less on the moon than on earth because the moon has a smaller mass than the earth. Therefore, its gravitational force is also smaller, it does not pull so hard. Each celestial body has its own gravitation. The banana will fall to the ground much more slowly on the moon because the moon doesn't pull it as hard.
A body's gravitational force is stronger the closer you are and the weaker the further away you are. We weigh a little less on a high mountain than on a much lower point. This is because we are much further away from the center of the earth or the core of the earth on the mountain.
The attraction of the earth or of other celestial bodies does not stop in space, it just becomes weaker and weaker. If you could throw a banana hard enough at the right angle, it would circle the earth. This is how rockets take astronauts into space. If you were to throw the banana much, much harder in the right direction, it would fly away from the earth and never come back - but our arms are not that strong.
Who discovered the solar system?
Anyone looking up at the clear sky can see seven bright objects. These are our sun, our moon, Mercury, Venus, Mars, Jupiter and Saturn. People had known about them for a long time. The Greeks and Romans believed that they were associated with the gods. In Babylon the days of the week were named after them. Almost everyone was sure that all things orbit the earth. They didn't know we were in one Solar system Life.
In 1543, Nicolaus Copernicus found out that the planets orbit the sun. Only the moon orbits the earth. But Copernicus was afraid to say that for most of his life. But then Galileo Galilei pointed his telescope at the sky. He found moons orbiting Jupiter. He was sure that Copernicus was right with his idea and got into great trouble when he said that. It took 70 years to convince scientists that the planets orbit the sun. But today almost everyone understands that we live in a solar system.
People built better telescopes and found many more things in the sky - moons, planets, asteroids. Even today more things are being found. Only recently did astronomers find things like Pluto. One will 2003 UB313, called and is larger than Pluto. Since August 2006, these Pluto-like objects have been called dwarf planets.
How did we explore the solar system? [Edit]
The image of the sun appears on a sheet of paper (year 1625).
Never let the sun shine directly in your eyes!
Before the telescope was invented, people explored the sky with their bare eyes. They saw the planets move across the sky. They learned to predict where the sun, moon, and planets would be in the sky. they built Observatories - these are places to watch the sky. They watch the sun and stars to tell the time of year. In China they even knew when the moon was covering the sun. Most people thought that Celestial bodies Can trigger wars or peace on earth.
After the telescope was first built, people kept improving it. Astronomers saw that the planets are not like the stars. There are worlds like the earth. You could see that some planets had moons. People began to think about what these worlds would look like. At first some thought that the other planets and moons were also inhabited by humans or animals. They wondered what it would be like to live on one of the other worlds. Then they built even better telescopes and saw that there are no plants or animals on the moon, let alone on Mars.
Now we can explore the other worlds by traveling there. A total of twelve astronauts were walking on the moon 30 years ago. They brought rocks and dust back to the earth. Probes flew past the planets Venus, Mars and the outer planets. The pictures they took showed us most of what we know about these planets today. Robots landed on Mars in 1971, 1976, and 1997. They took thousands of pictures of the planet. Two robotic probes, Spirit and Opportunity, are still working on Mars. They send us photos and videos back to earth. They also study what the stones and rocks on Mars are made of.
So far we haven't found any life except on earth. Perhaps small, single-celled creatures once lived on Mars. Perhaps there is life under the ice on Europa, one of Jupiter's moons. New missions are planned to investigate whether there is life anywhere on these worlds.
How did it come about?
Our solar system is part of the Milky Way Galaxy. Galaxies are large collections of dust, gases, stars and other celestial bodies. In our Milky Way Galaxy there are clouds of dust and gas in which new stars are formed. Our solar system was created in a cloud. Part of this cloud became smaller and less widely distributed. A thick, spinning disk of gas and small dust particles formed. This slice was thickest in the middle. Slowly the center collapsed until it became a sun. We are still researching how the planets were formed. Most scientists believe that they were created from the leftover gas and dust.
|The sun and the planets are formed from a disk of dirt and gases.|
It could have been like that. The rest of the disk continued to rotate around the sun. The small particles collided and some stuck. Little by little, the dust grew into granules, which in turn formed lumps the size of gravel, then pebbles and then stones. The collisions of the stones formed rocks, and the collisions of rocks became even larger things. These large structures swept the rest of the debris together and formed planets, moons, and asteroids.
The sun got hotter and hotter as it collapsed. She started to shine. The temperature in the center reached a temperature of one million degrees. The sun started producing a lot of light and heat. The light and heat displaced most of the remaining dust and gas between the inner planets. The light and the warmth are the sunlight that we can see and feel every day on earth.
What is happening to our solar system?
In about 5 billion years, the sun will have used up most of its fuel, i.e. the hydrogen. With that she will enter the last cycle of her life. It will collapse, and then the outer shell of the sun will expand. She becomes one Red giant.
It will become so big that some of the planets will be inside the sun. These planets will burn up. Which planets are destroyed depends on how much of the solar mass is lost. A strong solar wind will blow most of the outer shell away from the sun. The sun will therefore have much less mass. The sun's gravitational force is getting smaller. And the planets will move further away from the sun.
After becoming a red giant, the sun will start doing that helium to burn and thereby become even smaller. Then she is no longer a red giant. The sun will have used up its helium in about a hundred million years. Then it will become a red giant again and more gas will be blown away in the next hundred thousand years.
A planetary nebula will form. This can exist for a few thousand to a few tens of thousands of years. It will glow in the light of the sun.
In the center, the sun could shrink to a small star, the White dwarf is called. Such a star is about the size of the earth. It would take about a hundred such white dwarfs to be the size of today's sun. The sun has run out of fuel now. It has still stored a lot of heat and is slowly becoming cooler and cloudy. Then, in about a hundred billion years, their lights go out completely.
All links currently only lead to English websites.
Soon there will also be links to German-language pages here.
"About 500 years ago, however, a man we call Copernicus ..." 
"Then, about 100 years later, a man called Galileo ..." 
What is the solar system?
"None of the life on Earth ..." 
"Mercury has no moons." 
"Jupiter has 63!" 
"It is near the edge ..." 
"We call this the zodiacal glow." 
"The edge where the solar wind meets ..." 
- "Outside Our Solar System" at http://vathena.arc.nasa.gov/curric/space/spacover.html
- "Gravity is the force responsible for keeping the Earth and other planets in our solar system in orbit around the Sun." from Cosmic Glue, http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970108b.html
- Definitions of Mass, Gravity, and Weight from http://ksnn.larc.nasa.gov/webtext.cfm?unit=float
- Calinger, Ronald S. "Huygens, Christiaan." World Book Online Reference Center. 2004. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar268300 .; http://www.nasa.gov/worldbook/huygens_worldbook.html
- http://www.space.com/scienceastronomy/050729_new_planet.html; http://science.nasa.gov/headlines/y2005/29jul_planetx.xml; http://www.jpl.nasa.gov/news/news.cfm?release=2005-126
- Eclipse2001 museum http://museumeclipse.org/about/history.html
- Varadaraja V Raman: Glimpses of Ancient Science and Scientists Xlibris Corporation 2000, ISBN 073881363X, page 339 "The Chaldeans ... were also the first to suspect ... that the Sun, the moon, the planets and the constellation of stars, all affect human life and destiny .... These beliefs gradually spread ... to Egypt , China, Greece, India, and Rome, for example… astrology is still very popular. "
- http://vesuvius.jsc.nasa.gov/er/seh/mars.html; Sagan, Carl: "Mars and the Mind of Man", Harper and Row 1973, ISBN 0060104430; Verne, Jules: "From the Earth to the Moon" North Books 1995 ISBN 1582871035; From the Earth to the Moon on Project Gutenberg - http://www.gutenberg.org/etext/83;
- http://www.hq.nasa.gov/office/pao/History/SP-350/ch-15-4.html (bottom of page)
- http://www.nasa.gov/missions/solarsystem/Why_We_12.html; http://www.infoplease.com/spot/astronomy1.html
- Outline of Sun's death http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html
- Which planets may get destroyed http://www.public.iastate.edu/~lwillson/FuturSun.pdf
- Planetary nebulae http://www.seds.org/messier/planetar.html
- Has information on white dwarf stars http://math.ucr.edu/home/baez/RelWWW/tests.html
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