Astronomy_cls

=From Big Bang to Galaxies =  Our universe began 15 billion years ago. It exploded from nothing in the Big Bang. The universe started out smaller than the nucleus of an atom, and was very hot. In a quick flash, it became about the size of the earth now. Protons and neutrons began forming, matter and antimatter were formed and then smashed back into energy. The temperature continued to drop.  When the temperature got to 10,000 degrees Kelvin, electrons were able to begin rotating around the nucleus without getting ripped off. After three minutes, 1/4 of the particles formed Helium nuclei.

=Formation of Galaxies =

Galaxies began forming 2 billion years after the Big Bang. Galaxies are formed when gravity causes bits of matter that are close together to attract and clump together. When the universe was 3 billion years old, our galaxy was formed. It started as a clump of gas. Stars surrounded the clump, and created a halo. The rest of the gas became a disk surrounding the center of the galaxy. Galaxies can be elliptical, spiral, or irregular. Galaxies can collide. They used to collide more often a long time ago, but now they do sometimes. In the future, our galaxy may collide with the Andromeda galaxy.

=The Milky Way Galaxy =

The band of stars that is the milky way can be seen on a clear night. The light from the milky way comes from the stars. The dark part comes from clouds of opaque dust. The milky way is made up of a central bulge surrounded by a disk of stars and layer of gas and dust. The disk is 100,000 light years across and 1-2,000 light years thick. The bulge is 20,000 light years across. Our sun is in the disk, along with a dwarf galaxy that is attaching to the milky way galaxy. The galaxy is surrounded by a halo of stars. It is a spiral galaxy with four arms. The arms are made up of newer, blue stars, and bits of hydrogen. The bulge is made up of older, redder stars. =﻿Rotation of the Galaxy =

The galaxy is constantly turning. Each star is going around in its own orbit. It takes the sun 250 million years to go around the galaxy once. When we look at our galaxy, we don't see the outer layer called the corona to its full extent. The  corona has 10 times more material that we can see. Therefore the galaxy may be 5 times bigger than it looks. There is something that we call "dark matter" which causes the stars to spin more rapidly than they should, and we don't know why.

=﻿Formation of the Planets =

The sun formed like all stars, from a cloud of spinning dust. At the beginning of its formation, it was in the center, surrounded by a disk of gas and particles. Those particles began to stick together and form clumps, or planetecimals. These clumps became the planets. The largest ones were Jupiter, Saturn, Uranus, and Neptune. The ones who were closer to the sun couldn't get larger since there were so many collisions. Still, Mercury, Venus, Earth, and Mars were formed.

=Formation of Moons, Rings, and Comets =

The larger planets were strong enough that they could create disks too. Moons were formed from those disks. The smaller planets weren't strong enough to create moons in that way. Our moon was probably created when Earth crashed into a planet the size of Mars. The moon got its craters from constant bombardment for a billion years. The planetecimals mentioned before eventually got destroyed from collisions, sent outside of the solar system, went into the asteroid belt located between Jupiter and Mars, or became moons for the larger planets. Icy planetecimals became comets. Rings around the larger planets are made up of comets and other planetecimals attracted to the planet by gravity. Large asteroids and comets crashed into Earth often a long time ago, but not as often currently. But those asteroids and comets could be the reason why the now extinct species were wiped out.



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