Astronomy_ses

=The Big Bang= The big bang formed from a simple explosion, an explosion that happened from nothing. This explosion happened 15 billion years ago. It started out the size of an atomic nucleus. In a split second, the universe expanded from the size of a nucleus to the size of the earth. Before the universe is a tenth of millisecond old, protons, neutrons, and anti-protons were forming. This didn't happen until the temperature dropped to 3,000 degrees Kelvin. Protons and anti-protons are created from radiation and then they annihilate and turn into radiation again. After one second the temperature in the universe has cooled to ten billion degrees. After 3 minutes, the helium and hydrogen have combined to form nuclei, and the electrons that once were just roaming around, started to orbit the nuclei.

= The Formation of Galaxies = The formation of Galaxies began about two billion years after the Big Bang. Then the gravity causes sponge like structures to appear in the universe. Then, a full galaxy formed one billion years later- when the universe was three billion years old. At this point, the galaxies were huge spheres of gas. Galaxies are classified by their shape. All galaxies are either irregular, spiral, or elliptical. An elliptical galaxy is sort of like an egg shape, but they are much larger than eggs. A spiral shaped galaxy looks somewhat like the top view of a hurricane. This is because there are arms on a spiral galaxy that flare out. There are also irregular galaxies that are just blobs of gas and have no exact or defined shape.

= The Milky Way Galaxy = The Milky Way Galaxy is the galaxy in which we are located. The Milky Way has a disk of stars that is about 100,000 light years across and 1,000-2,000 light years thick. In the center of this disk, there is a very thin layer of gas and dust. Then, in the center of the galaxy there is a bulge called the central bulge. This bulge is approximately 20,000 light years across and made up of red and orange stars, which are very old. In the center of the Central Bulge, it is predicted that there is a black hole surrounded by gas. The Milky Way does not move as a whole when it rotates. Each star and gas cloud is in their own orbit. When everything is spinning, matter temporarily piles up in the spiral arms, but then everything starts moving again.

 = History of our Solar System = Jupiter, Saturn, Uranis, and Neptune are coincidered large planets, and were formed in what is now the outer solar system. They all formed disks of their own and moons condensed. The gravitational pull what about ten times greater than the earth's on these planets, so therefore they were able to hold onto gasses from the surrounding nebula. After these, in the inner solar system, Terrestrial planets were formed. No larger planets were able to form in the inner solar system because there were too many collisions. The terrestrial planets (Earth, Mars, Mercury and Venus), were able to keep their heat by inner radiation, and bombardment by outside objects. Then, all of the metal sank to the middle of the planets, and they cooled off and solidified. Our moon was probably created by a massive collision by the earth and another planet about the size of mars.

= Formation of things in our Universe = In the universe, there were rocks that were about one kilometer across, and were called planetessimals. These planetessimals crashed into one another and depending on their movement either broke into tiny pieces, or formed one giant planetessimals. Moons, when they were first created, went through heavy bombardment for about one million years. Eventually, most of the planetessimals were in very tiny pieces due to collisions and were sent out of the solar system. The only other option for planetessimals was for them to go to the asteroid belt between Mars and Jupiter. A few of the planetessimals were captured as the moons of planets. Planetessimals from the outer solar system that are freezing cold sometimes reach the sun. Once they do this they are formed into comets. The rings around planets are most likely made out of stray planetessimals and comets that are being pulled in by the gravitational pull when they get too close to the planet.



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