Astronomy_omg23

= From Big Bang to Galaxies =

What we are in now had to start from something, and that something is called the big bang. The big bang is and explosion that began about 15 billion years ago and is continuing to occur today. In the beginning, everything was packed together extremely tightly and was ridiculously hot. There was an sudden explosion and in less than a millisecond, protons and neutrons were formed. In about five seconds, the universe expanded to the size of the Earth, and then continued on at a steady pace for billions of years. Matter and anti-matter were created by the radiation but most of them were destroyed. Over the years, the temperature of the universe dropped steadily, and when it reached about 3000 degrees kelvin, atoms are created. These atoms go on and more are created. Eventually, planets are formed and then come the animals.



= Formation of Galaxies = About two billion years after the explosion called the big bang occurred, galaxies were created. They are formed by clumps of matter getting pulled together by the force of gravity. The Milky Way galaxy was formed about three billion years after the big bang. It started out being an extremely large ball of gas, but gravity squished it into a disk, with a bulge in the center. Four long, spiral arms grew out of the center of the galaxy. Each galaxy is classified by its shape. It can be an elliptical, a spiral or an irregular galaxy. The Milky Way is a spiral galaxy. In the early universe, the galaxies were much closer together than they are now, so collisions were much more common. But someday in the future, the Milky Way Galaxy might collide with the Andromiter galaxy.



= Structure of the Galaxy =

The Milky Way galaxy is one of the very many galaxies in the universe. It is an insiders view of the galaxy. It is actually an extremely large disk of matter that has a very large bulge in the center of it. The sun and our solar system is about half way from the central bulge to the outskirts of the galaxy. It is hypothesized that there is a massive black whole at the center of the universe, or the nucleus, due to the huge amount of energy that the central bulge produces. The central bulge is made up of millions of stars, most of which are old and red. Our galaxy is probably surrounded by an invisible corona that contains ten time more material than we are able to see. Since we are so incredibly small compared to the galaxy, it is hard to tell exactly how large it is, but the Milky Way galaxy might actually be about five times larger than we are able to see.



= Rotation of the Galaxy =

The entire galaxy is spinning, but it is not stiff or rigid, like a disk, because each star and gas cloud has its own orbit. The legs or the spirals all rotate in one directions together, but everything else, such as the stars, travel in the opposite direction. It takes about the 250 million years to travel in a full circle, traveling at 250 kilometers per second. The spiral arms are where matter piles up, so the are able to spin in one direction. Because of the way that we rotate, we are able to ell that we have the corona that surrounds us.



= Formation of Planets =

Everything had to be created, even planets and stars. The sun was formed when gravity pulled together a cloud of interstellar gas and dust. This created a ball of rotating gas. The rotating ball collapsed to a disk and inside of that disk, solid material, called planetessimals, were formed. Some of these planetessimals crashed together and created larger ones, while other were destroyed on impact. The creation of these large planetessimals was what formed the large planets in the outer solar system. These planets are Jupiter, Saturn, Uranus and Neptune. In the inner solar system, the four terrestrial planets were formed, which are Venus, mercury, Earth and Mars. There surfaces were heated by constant bombardment of other rocks floating in the galaxy. The lighter rocks on the planets rose to the surface and solidified while the heavier ones sank to the middle of the planets.



= Formation of Moons, Rings and Comets =

Just like planets, moons, rings and comets all had to be created. Most of them were created by planetessimals that were floating around in space, but some of them are different. Rings are created by many planetessimals that were attracted to the planet by the gravitational pull and them began to orbit with the planet. Comets are created by icy planetessimals that aimlessly float around space. Most moons are very small compared to the planet, so the gravitational pull of the planet is able to pull the small rock into its orbit and make it a moon. Earth's moon is a different situation. It is a very large moon given the size of the planet that it orbits. It is most likely that our moon was created by a collision with the earth and another planet in the early galaxy. The gravitational pulls attracted until they collided and the moon was part of the outcome. Like most moons, ours has a rocky surface because it had been bombarded by other rocks for 1,000,000 years.



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