astronomy_adm


 * From Big Bang to Galaxies **


 * The Bing Bang is the most popular theory. Our universe exploded out of nothing and in a flash it went from the size of an atom to the size of the earth. Within 1 second, it was one billion degrees. Within 3 minutes the protons and neutrons started to form helium nuclei. The universe still expanded and the temperature still fell. Within 300,000 years atoms formed and created Hydrogen and Helium. 2 million years later, the galaxies begin to form. **



** Formation of Galaxies **

** The formation of galaxies is extremely interesting because the different parts have an unimaginable amount of stars in them. The galaxies grew clumps and the Universe became sponge-like. Our galaxy formed when the universe was three billion years old. It started as a sphere of gas and Glob lice clusters scattered through the sphere which is not the halo. The Galaxy started to form a disk around the central bulge and spiral arms developed. The different kinds of galaxies are optical, spiral, and irregular. The arms can be tightly would or loose. **



** Structure of the Galaxy **

** The Structure of the Galaxy is a complicated structure and is unbelievable long. It is made up of mostly dust and stars and is 100,000 light years long. A flat disk of stars about 100,000 light years across and 1,000-2,000 light years thick is the outer layer of the galaxy. Gas and dust is even thinner of a layer and it is across the middle of the disk. The Central Bulge is a large bulge about 20,000 light years across. Stars and star clusters are scattered in a halo 130,000 light years from the center of the galaxy. Four spiral arms made of different stars come out from the bulge. The middle of the bulge (5 light years) is the nucleus of the galaxy and is probably a massive black hole. **



** Rotation of the Galaxy **

** The Rotation of the Galaxy is a misunderstood concept and is confusing. The whole galaxy is turning but not like a rigid disk. Each star and gas cloud is orbiting on its own. The sun takes 250,000,000 to go around once traveling at 250 kilometers a second. The spiral arms are when the matter temporary piles up, not permanent structures that rotate together. **



** Formation of the Planets **

** The formation of planets varied by each planet. The sun formed when gravity pulled together gas. In the suns disk matter started to collect into larger particles. They were called planetessimals and were few kilometers across. Icy planetessimals survived far from the sun. The closer ones were rock and metal. The outer solar system includes the four larger masses known as the Giant Planets which are Jupiter, Saturn, Uranus, and Neptune. The Four Terrestrial planets in the inner solar system are Mercury, Venus, Earth, and Mars. In these planets the metal went to the middle of the rock and the lighter rock rose to the surface, cooled and solidified. **



** Formation of Moons, Rings, & Comets **

** Other smaller rocks form in different ways and in different groups. Moons are created by collisions or when gravity pulls on large rocks. Their surfaces are heated by constant and heavy bombardment of rocks. Icy Planetessimals become comets if they reach the warm vicinity of the sun. Rings are formed by stray planetessimals that are being broken apart by gravity. **



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