Astronomy_jlc

=Astronomy Parragraphs =

From the Big Bang to Galaxies
==The big bang was the start of the universe, it took millions of years just to create the first galaxy. The universe expanded from the size of the nucleus of an atom to the size of the earth in one second. Then, the expansion of the universe happened at a steady rate as the temperature dropped. When the temperature falls to 3000 o K, electrons can start to orbit atoms. That was when the first hints of structure began to appear. Two million years later, galaxies began to form. ==

The Formation of Galaxies
==Galaxies start as a huge sphere of gas. Some start formed in globular clusters, scattered through the sphere. This is now the halo of the galaxy. The rest of the gas settled into a disc around a central bulge and spiral arms developed. Galaxies are classed according to their shape as elliptical, spiral, or irregular. In the early universe, galaxies were much closer together than they are now. Collisions and merges were much more common. Collisions can induce spiral arms to grow. Galaxies colliding head on can collide into one galaxy. ==

The Milky Way
==The milky way can be seen on some clear nights. The large cluster of lights are the stars clustered together in the edge of the galaxy. Viewing it from half a million light-years away, looking at it's side, you can see all of the different parts of it. There is a flat disc of stars about a 100,000 light-years across and about 1,000 to 2,000 light-years thick. An even thinner layer of gas and dust cuts across the middle of the disc. At the center, there's a large, flat, bulge about 20,000 light-years across. The sun lies in the disc about halfway out from the galactic center. On the other side, about halfway, there is another, dwarf galaxy, merging with the milky way. Globular star clusters and other stars stretch out in a halo around our galaxy. There are four spiral arms stretching out from our galaxy. They are marked by bright bluish, young, stars and pink clouds of glowing gas. ==

The Rotations of Stars
==Our galaxy and every other galaxy in the universe rotates. Our galaxy rotates counter clockwise. However, each star has it's own rotation. Our galaxy rotates, and it's rotation tells us that we are surrounded by an invisible corona containing 5 times more mass that we actually see. That is made up of stars and other gas. While our galaxy rotates one way, the stars and gas rotate in the opposite direction, in the formation of our spiral arms. ==

Solar Systems
===The planet's were all formed around our star, the sun. The sun formed a disc that is our solar system. In that disc, rocks collided to form planitecimles. They then began to collide with each other. Mostly, they broke when they collided, but some collided gently enough to create larger objects. In the outer solar system, four larger objects were formed. They became the planets Jupitern, Saturn, Uranus, and Neptune. In the inner solar system, there were too many collisions for any large planets to form. However, finally four planets formed, Mercury, Venus, Earth, and Mars. That is how the planets formed around our sun. ===

Moons, Rings, and Comets
===Moons, rings, and comets formed around the eight planets in the solar system. The planets grew discs of their own, in witch moons condensed, the same way that the planets condensed around the sun, only on a smaller scale. Comets are icy planitecimles that come down into the inner atmosphere around the sun. Rings around the planets are a result of stray planitecimles and comets breaking up in a planet's atmosphere. Most planitecimles, however, had settled in the asteroid belt between Mars and Jupiter. Other planitecimles were captured as the moons of planet's. ===

[[image:jlc_comet.JPG width="370" height="292"]]
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