Earth spins, or rotates, on its axis. An axis is an imaginary line through Earth from the North Pole to the South Pole. It takes Earth approximately 24 hours to make one rotation on its axis. Because of this motion, any place on Earth experiences a(n) cycle of day and night. We know Earth is spinning because of data collected by satellites. A Frenchman named Foucault also discovered evidence of Earth spinning. He hung a heavy pendulum that knocked down many pegs. Earth’s shape is not really a(n) sphere. At the North and South Poles, Earth is slightly flattened. And at the equator, Earth bulges slightly.