Soil is lower-case “earth.” And in most uses even the planet itself remains humbly in lower-case letters: “peace on earth.” But in astronomical contexts, the Earth comes into its own with a proud initial capital, and in science fiction it drops the introductory article and becomes “Earth,” just like Mars and Venus. A similar pattern applies to Earth’s satellite: “a beautiful harvest moon,” but “the craters of the Moon.” Because other planets also have moons “the Moon” retains its article, unlike “Earth.”