A submarine, scooting through the depths, shoots sound waves to probe the mountains and valleys of the ocean floor, allowing humans to explore that inhospitable realm. The Hubble Space Telescope takes snapshots of scenes billions of light-years away, revealing vistas vastly beyond the limits of the human eye. Yet we need not venture to treacherous places to enhance our perception of our home planet. A compass tunes hikers to the earth’s magnetic field, endowing them with knowledge of north and south as they wander through the woods.