"First, a brief tour of the worldview of a flat-earther: While writing off buckets of concrete evidence that Earth is spherical, they readily accept a laundry list of propositions that some would call ludicrous. The leading flat-Earther theory holds that Earth is a disc with the Arctic Circle in the center and Antarctica, a 150-foot-tall wall of ice, around the rim. NASA employees, they say, guard this ice wall to prevent people from climbing over and falling off the disc. Earth's day and night cycle is explained by positing that the sun and moon are spheres measuring 32 miles (51 kilometers) that move in circles 3,000 miles (4,828 km) above the plane of the Earth. (Stars, they say, move in a plane 3,100 miles up.) Like spotlights, these celestial spheres illuminate different portions of the planet in a 24-hour cycle. Flat-earthers believe there must also be an invisible 'antimoon' that obscures the moon during lunar eclipses.