Craters on the Moon and Mars

Abstract

When Galileo first turned his small telescope to the Moon in 1610, he observed a number of craters, their walls shining in the light of the slowly rising Sun. As astronomers explored the Moon and planets with early telescopes, what impressed them was not the unusualness of lunar craters, which seemed to them rather like familiar volcanoes, but that the Moon and planets looked so similar in many ways to our own world. Over ensuing centuries, people speculated about the inhabitants of these heavenly bodies. Astronomers observed different colors and forms of surface features, noted the presence or absence of clouds, and remarked on other disparities between the Moon, the planets, and Earth. But such variations were accepted as no greater than those between the deserts of Arabia and the countryside of England.