Units of meters (or kilometers) works well enough for things as big as the Earth, with a radius of about 6.37 x 10 6 meters. However, outside of the Earth stuff starts getting super big.

Matt Cooper has no illusions about the hazards of diving from a 27-meter platform — about 90 feet, or as high as a nine-story building — into the sea, a lake, or a diving tank. “Even if it ...