We started our astronomy class by talking about how everything began. The word cosmology means the study of the origins of the universe, and people have wondered throughout history and pre-history where we and everything else came from. The theory that most scientists believe is called the Big Bang, and basically it's that there was a giant explosion nearly 14 billion years ago that everything in the universe came out of. In a fraction of a second, matter was created. It took about a billion years for the first stars to form, and our galaxy, the Milky Way, has some stars that old.
The Milky Way is a spinning galaxy, with spiral arms that come out from a giant black hole in the center. Our sun is only one star in the galaxy and there are about 200 to 400 billion other stars in the Milky Way. Here's a map of where our sun and solar system are in the Milky Way.
Our galaxy is right now eating up another galaxy called the Canis Major Dwarf Galaxy, and we have eaten up other galaxies before. We're cannibals!!! Also, the nearest other galaxy, Andromeda, is headed for a collision with us, which will happen in about 4 billion years. Here's a video simulation of what scientists think it was like when our galaxy formed. Basically, the gases started to blob up and fall together and spin, and some blobs squished themselves up so much they became hot and formed stars.
Our solar system formed about 4.6 billion years ago when a cloud of dust and gas collapsed. Then the sun formed when dust and matter squished together so much that it became a hot ball. The rest of the stuff started spinning and formed the planets and their moons. There are still chunks of debris floating around in the asteroid belt and the Oort cloud.
Next week we'll learn more about the history of our solar system -- it was pretty violent!
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