The time it takes for the Earth to rotate once on its axis is called a "day." Specifically, a solar day, which is approximately 24 hours long, is the duration from one noon to the next, as measured by the position of the sun in the sky. Earth's rotation is responsible for the cycle of day and night. However, there is also a sidereal day, which is roughly 23 hours and 56 minutes, representing the time it takes for Earth to complete one full rotation relative to distant stars. This differentiation is essential in understanding celestial mechanics.