1. Why do we study the Earth in an Astronomy class? Use the word analog in your answer.

Before the scientific search for and study of extrasolar planets, the possibility was argued through philosophy and science fiction. The mediocrity principle suggests that planets like Earth should be common in the Universe, while the Rare Earth hypothesis suggests that they are extremely rare. The thousands of exoplanetary star systems discovered so far are profoundly different from the Solar system, supporting the Rare Earth Hypothesis.