Astronomy_CJS

__**From the Big Bang to Galaxies**__

15 billion years ago, The Big Bang was the creation of everything, including galaxies. The Big Bang happened when the tiny, dense, hot amount of matter exploded and started to expand very rapidly into the nothing. All the molecules and quarks were spinning and flying around, sometimes faster than light. Within 10 -24 seconds, the universe had begun to cool and had expanded to the size of our sun. Once our universe had cooled enough, the quarks created nuclei and the electrons began to circle the nuclei. These electrons created the first atoms; helium and hydrogen.



__** Formation of Galaxies **__

The formation of galaxies is a violent and slow process. Galaxies are vast collections of stars, gases, and dust. Galaxies form when large chunks of dust and gas collect together. This dust and gas has gravity, and keeps drawing in more and more gas and dust. Soon, so much gas and dust is drawn in that the center collects a ring of dust and gas around it that is millions of light years across. In most cases, the gas in the center collapses into a supermassive black hole. In the beginning of the universe, Galaxies were much closer and collisions happened relatively frequently. Galaxies would collide and spiral arms would form from the disruption in the spinning gas.



__** Structure of the Galaxy **__

Our galaxy, the Milky Way Galaxy, is, like all galaxies, a vast collection of stars and gases. Our solar system is halfway out from the center of our galaxy, which is 1 million Light years across. Our galaxy is a huge disk that has four rotating spiral arms. In between the top and bottom of these arms, there is a relatively thin layer of gases. In the center of our galaxy, we believe there is a black hole, which maintains a giant globe in the center by using it's massive gravity.



__**Rotation of the Galaxy**__

Our galaxy rotates like many other galaxies, seeing that it is a spiral galaxy. It has four giant arms that rotate around a central globe. In this globe, there is most likely a giant black hole. The galaxy also rotates in a circle with three other galaxies. Nearest to the black hole is where the majority of the suns are and the gases around the black hole rotate around it, giving it the appearance of being massive.



**__ //Formation of the Planets// __**

Planets are formed in two ways, depending on the planet. Gas giants, such as Uranus, Saturn, Neptune, and Jupiter were formed first by the sun. Excess gas and dust from the sun was blown off and collected into clumps to form the gas giants. These Gas giants have large dense atmospheres. Then came the terrestrial planets. These planets (Earth, Mars, Venus and Mercury) are much closer to the sun and are much smaller than gas giants. They were formed when giant rocks known as planetessimals that had been spinning around the sun, started to get stuck together and formed larger and larger clumps. These clumps had smaller atmospheres and no atmospheres in the beginning.



//Formation of Moons, Rings, & Comets//

Moons, Rings, and Comets all formed from the same thing; planetessimals. These hunks of rock that had been spinning around the sun were thrown away when the sun became and actual star. For the bigger planets, moons were just captured planetessimals and were much smaller than the planets themselves. Also, the bigger mass meant that they had a greater potential for making rings like on Uranus and Saturn. These rings are planetessimals that these planets have captured and crushed into dust. This dust then rotates around the planet and streamlines into a disk. For smaller planets, moons are harder to come by. Our moon most likely came from a smaller planet (around the size of Mars) colliding with us in the early years of our planet. This planet knocked up dust and debris that condensed into a proportionally larger moon. Comets are nothing more than cold, icy planetessimals that went to close to the sun, and the solar wind heated it up and pushed some matter behind it in a "tail".



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