Our planet spins on its axis once every 24 hours. Because the Sun is stationary (relative to us), this spin constantly changes which part of Earth faces the light.
The Earth is not stationary; it spins like a giant top. An "axis" is an imaginary line that runs through the center of the Earth from the North Pole to the South Pole. As the Earth rotates on this axis, different parts of the planet face toward the Sun, while other parts face away. causes of day and night on earth