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Roughly how many stars make up the milky way?

What is a light year?

Briefly describe parallax and how it's used to measure the distance of nearby stars.

Explain why we see stars and galaxies as they were in the past.

What is red shift?

Explain the evidence that shows that the universe is expanding.

Name the process that wears mountains down.

Briefly explain Wegener's theory of continental drift.

Give three reasons why Wegener's theory was rejected at first.

How fast are some sea floors spreading each year?