Key concepts(25.3)
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Describe the size and structure of the Milky Way Galaxy
The Milky Way is a large spiral galaxy whose disk is about 100,000 light years wide and about 10,000 light-years thick at the nucleus.
What is the big bang theory?
The big bang theory states that at one time, the entire universe was confined to a dense, hot, super massive ball. Then, about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions.
How do galaxies differ?
In addition to shape and size, one of the major differences among different types of galaxies is the age of their stars.
What evidence indicates that the universe is expanding?
The red shifts of distant galaxies indicate that the universe is expanding.