The Moon is the most viewed object in the sky, the Sun being too bright to look at directly and the planets too far away. The Greeks deduced everything that could be learned about the Moon using only the naked eye, including that it has no light of its own but reflects that of the Sun. They understood the cause of eclipses and used the Earth's shadow on the Moon to conclude that our planet is a sphere and to calculate the size of both the Moon and the Earth. The invention of the telescope some two millennia later offered the opportunity for much greater understanding, but the early observers became sidetracked onto a dead end: First, they fooled themselves into believing that they saw evidence of life on the Moon, even the works of a civilization. Second, they became convinced that the craters of the Moon were volcanoes like those we have on the Earth. These wrong-headed beliefs took centuries to dispel. The origin of the Moon itself has proven an even more difficult question, but scientists have now closed in on the answer. They find that our placid and seemingly unchanging Moon was born in colossal violence as a planet the size of Mars crashed into the primordial Earth and flung off a blob that solidified to become our heavenly companion. Unlocking the Moon's Secrets follows these developments to show how science evolves, complete with misunderstandings, contentious arguments, difficult to relinquish assumptions, and shifting views as new facts come to light. Thanks to the work of generations of determined scientists, we understand our Moon, at last.